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(1)國立臺灣體育運動大學 National Taiwan University of Physical Education and Sport. 體育研究所碩士學位論文. 增強式跳躍訓練之跳箱訓練的下肢生物力學分析 Biomechanical Analysis of Lower Limbs during Plyometric Exercise – Box Jump. 研究生：陳彥妃撰指導教授：吳鴻文博士. 中. 華. 民. 國. 1 0 2 年. 1 月.

(2) 中文摘要. 增強式運動是一種常見的訓練方式用來增加運動員的爆發力與運動表現，近年來，這種運動方式也常常被拿來作為傷後運動員在重返運動場之前的復健方式。本篇研究的目的是比較增強式運動之中的兩種跳箱訓練 (跨越跳箱與跳上跳箱 )以及探討不同跳躍速度下 (每分鐘 60 下、 75 下與 90 下 ) 對於強度與人體的影響。實驗的受試者是 1 2 名國立台灣體育運動大學田徑校隊的健康男性運動員。我們使用三維動作分析系統與兩塊測力板來收集在跳箱跳躍過程中的下肢運動學與動力學參數。結果顯示跳上跳箱的這種方式比跨越跳箱的方式在最大膝關節屈曲角度的時候有較多的髖關節與膝關節屈曲角度、較長的到達最大膝關節屈曲角度的時間以及能提供前十字韌帶較高的穩定度。在跳躍速度方面，每分鐘. 90. 下的速度能夠產生比較小的髖關節內收角度、膝關節外翻角度與較小的膝關節內 /外翻力矩以及內 /外旋力矩。. I.

(3) Abstract. Plyometric exercise is widely used as a training program for competitive athletes to increase their explosive power and to improve their performance. Also, it is getting popular to be used as a therapeutic exercise for post-injured athletes to help them to return to sports. The purpose of this study was to compare two plyometric box jumps (cross the box and front the box) and to investigate the effect of different jumping speeds (60 bpm, 75 bpm and 90 bpm) toward the intensity and human body. Twelve healthy, male athletes were recruited from track and field team in National Taiwan University of Physical Education and Sport. Kinematics and kinetics data of lower extremities were collected via three-dimensional motion analysis system and two force plateforms during the box jumping tasks under three different rates. We found that front the box (FB) had more hip and knee flexion at the checkpoint of maximum knee flexion, more time to maximum keen flexion and better ACL stabilization than cross the box (CB). While 90 bpm had less hip adduction, knee valgus and knee valgus/varus moments as well as internal/external rotation moments. According to our finding, we suggest that FB and 90 bpm are more suitable to be included in the training protocol for post-injured athletes in the return to sport phase of rehabilitation.. II.

(4) 謝誌. 本論文得以完成，需要感謝的人很多，若非大家的多方協助，本論文恐無法順利完成。首先，我要感謝我的指導教授吳鴻文老師，感謝老師耐心的指導、在課業及論文上的解惑與啟發以及適時的在我遇到瓶頸的時候給與靈感及鼓勵。再來要感謝本校田徑校隊跳部的指導教練乃慧芳老師在受試者方面的大力幫忙，讓我有幸與這麼多優秀的選手合作。當然也很感謝參與本實驗的受試者，在隊訓之後還要抽空來參與實驗，他們的精湛表現與良好紀律令人驚豔。另外，我也要感謝研究室的伙伴們，感謝凱涵學姐提供在課業與實驗上的諮詢。感謝同窗戰友崇富在實驗、分析、撰寫 …等各方面不厭其煩的討論與幫忙。感謝亭妤在辦公室軟體使用上的即時解答。感謝予藍陪我一起採買實驗跳箱的補強用品，並且陪我一起揮鐵鎚、釘釘子把跳箱弄得更堅固以及後續實驗中的協助。感謝榕津在跳箱製作上的連絡與運送。還有感謝研究室學弟妹，泇達、佳融、姍姍、仲天、智勛、杏姿在實驗上的幫忙。還有要特別感謝實驗的固定班底偉恩學弟風雨無阻的大力相助，讓實驗能夠順利完成。最後，我要感謝我最親愛的家人，因為他們的諒解與支持，讓我能夠毫無後顧之憂的專心於學業上並全心的完成論文。. 要感謝的人、事、物真的太多了，無法在此一一詳述。謹以此文，獻給大家。願大家同我一起分享這份喜悅。. III.

(5) Contents Chinese Abstract ................................................................................................................ I Abstract ............................................................................................................................ II Acknowledgements ......................................................................................................... III Contents .......................................................................................................................... IV List of Tables................................................................................................................... VI List of Figures ................................................................................................................VII Chapter 1 Introduction ...................................................................................................... 1 1.1 Preface ................................................................................................................ 1 1.2 Purpose................................................................................................................ 5 Chapter 2 Literature Review ............................................................................................. 6 2.1 Introduction of Plyometric exercise .................................................................... 6 2.2 Training Plan of Plyometric exercise ................................................................ 13 2.3 Adaptations after Plyometric exercise .............................................................. 20 2.4 Plyometric exercise & Resistance training ....................................................... 22 2.5 Clinical application of Plyometric exercise ...................................................... 25 Chapter 3 Material and Methods .................................................................................... 27 3.1 Subjects ............................................................................................................. 27 3.2 Experimental Instrumentation........................................................................... 28 3.3 Experimental Procedures .................................................................................. 31 Chapter 4 Results ............................................................................................................ 40 4.1 Joint Kinematics & Kinetics during Different Box Jumps ............................... 40 4.2 Joint Range of Motion (ROM) in Different Box Jumps ................................... 55 4.3 Peak Joint Forces in Different Box Jumps ........................................................ 59 4.4 Peak Joint Moments in Different Box Jumps ................................................... 61 Chapter 5 Discussion ...................................................................................................... 63. IV.

(6) 5.1 Joint Kinematics & Kinetics during Different Box Jumps ............................... 63 5.2 Range of Motion (ROM) .................................................................................. 72 5.3 Joint Forces and Joint moments ........................................................................ 76 Chapter 6 Conclusion...................................................................................................... 81 Reference ........................................................................................................................ 82 Appendix A- Subject Information & Anthropometry ..................................................... 83 Appendix B- Subject Consent......................................................................................... 83 Appendix C- Research Ethics Committee Approval ...................................................... 83. V.

(7) List of Tables Table 3.1. Subject information (Mean±SD) .................................................................... 27 Table 3.3-1. Marker set attachments............................................................................... 34. VI.

(8) List of Figures Figure 2.1-2. Standing jumps ......................................................................................... 10 Figure 2.1-3. Multiple jumps and hops .......................................................................... 10 Figure 2.1-4. Box jumps ................................................................................................. 11 Figure 2.1-5. Depth jumps .............................................................................................. 12 Figure 3.2-1. Laboratory setting ..................................................................................... 28 Figure 3.2-2. VICON motion analysis system ............................................................... 29 Figure 3.2-3. Kistler force plateform .............................................................................. 29 Figure 3.2-4. Plyometric box .......................................................................................... 30 Figure 3.3-1. Experimental procedures .......................................................................... 31 Figure 3.3-2. Wand ......................................................................................................... 32 Figure 3.3-3. L-frame ..................................................................................................... 33 Figure 3.3-4. Cross the box ............................................................................................ 36 Figure 3.3-5. Front the box ............................................................................................. 36 Figure 3.3-6. Plyometric boxes and force plateforms .................................................... 37 Figure 4.1-1. Hip joint angle, joint moment and joint force of cross the box (CB) during box jump ................................................................................................................. 42 Figure 4.1-2. Hip joint angle, joint moment and joint force of front the box (FB) during box jump ................................................................................................................. 44 Figure 4.1-3. Knee joint angle, joint moment and joint force of cross the box (CB) during box jump ...................................................................................................... 46 Figure 4.1-4. Knee joint angle, joint moment and joint force of front the box (FB) during box jump ...................................................................................................... 48 Figure 4.1-5. Ankle joint angle, joint moment and joint force of cross the box (CB) during box jump ...................................................................................................... 50 Figure 4.1-6. Ankle joint angle, joint moment and joint force of front the box (FB) during box jump ...................................................................................................... 52 VII.

(9) Figure 4.1-7. Time to maximum knee flexion of different box jumps under different rates ......................................................................................................................... 54 Figure 4.1-8. Total foot contact time of different box jumps under different rates ........ 54 Figure 4.2-1. ROM - Interaction effect........................................................................... 56 Figure 4.2-2. ROM - Non-interaction effect................................................................... 58 Figure 4.3. Peak joint forces of lower limbs in different box jumps and rates............... 60 Figure 4.4. Peak joint moments of lower limbs in different box jumps and rates .......... 62. VIII.

(10) Chapter 1 Introduction. 1.1 Preface. Improving performance is one of the most important things for athletes and there are many studies confirmed that pl yometric. exercises. could. effectively. elevate. explosive. power as well as enhance the performances for athletes in the c o m p e t i t i o n s . R e c e n t l y, t h e r e a r e a l s o g e t t i n g m o r e f o c u s e s o n pl yometric exercise as a therapeutic program for high -level athletes on the return-to-sports phase of rehabilitation. It is not difficult to understand why the plyometric exercises are getting. popular. as. a. means. of. therapeutic. programs. for. post-injured competitive athletes in th e return-to-sports phase of rehabilitation because it is unlikely for them to adapt the excessive stress and the demanding intensity in return-to-play if they cannot cope with what the plyometric exercises would impose upon them.. According to the properti es of the pl yometric exercis e – multiple repetitions, high impacts, high intensities and high loadings, this form of exercise helps athletes to enhance jumping. performance,. increase. explosive. p o w e r,. increase. c o n c e n t r i c v e l o c i t y a n d i m p r o v e a g i l i t y ( To u m i , B e s t , M a r t i n & P o um a r at , 2 0 04 ) . H o w ev e r, t h e d e ma n ds of th e ex e r ci s e al so 1.

(11) lead to high risk of injuries if the athletes didn ’t meet the criteria before implementing plyometric exercise into their training programs (Chu, 1998; Hreljac et al., 2000; Potach & Chu, 2000) and let alone for post -injured athletes. In this case, t h e p r o t o c o l s , i n t e n s i t y, a n d t h e v o l u m e o f t h e p l y o m e t r i c exercise should be designed and chosen more carefully in order to benefit from the adaptation s and effects of the exercise and, at the same time, to minimize the potential risk s during the training sessions.. The. criteria. of. return-to-play. include. full. range. of. motion (ROM), pain-free movement, and a certain level of muscle strength needed in the following activities. (Saal,. 1991). The training protocols emphasized in this phase are undoubtedly. sport-specific. that. pl yometric. exercise. and. agilit y training are usuall y included. Pl yometric exercise is defined as the muscles perform a quick eccentric contraction before doing the concentric contraction (Chu & Plummer, 1984), while agility training involves movements with quick changing directions, sudden stopping/starting and twisting (Fitzgerald, Childs, Ridge & Irrgang, 2002). There are also many studies proved that a combinatio n of pl yometric exercise and resistance training is more effective in lower extremit y strengthening, tissue adaptation and injury reduction than any other forms of training alone (Mclaughlin et al., 2001).. 2.

(12) Although plyometric exercises are widely utilized in various training regimens for performance improvement or rehabilitation, there is still no formulated way to clarify the determination of the intensity as in resistance/weight training. Therefore,. quantifying. pl yometric. exercise. become s. an. important issue for researchers in this field. In the previous studies, Jensen and Ebben (2005) evaluated the intensity of eight. different. pl yometric. exercises. through. measuring. impulse, rate of eccentric force development (ERFD), ground reaction force (GRF), and knee joint reaction forces. The pl yometric exercises in their study consisted of drop jumps (DJ) from 46cm and 61cm in height, pike jump, tuck jump, single leg jump, countermovement jump, squat jump and squat jump with 30% 1 RM. Another intensit y of pl yometric exercise w a s g r a d e d i n E b b e n ’s e x p e r i m e n t ( 2 0 0 8 ) b y c o m p a r i n g t h e recruitments of quadriceps through electrom yography (EMG). In. 1998,. Chu. suggested. pl yometric jumps. were. that. the. classified. intensity. of. different. according to the. effort. involved in a task. The intensity for jump training exercises, under his classification, from low to high were jump -in-place, standing jump, multiple jumps and hops, box drills and depth j u m p s ; h o w e v e r, t h e r e w e r e n o d e t a i l d e s c r i p t i o n s o n e a c h jump. In the meanwhile, he also addressed that the numbers of foot contact could be used as a standard for training volume, but that was also a general principle. Therefore, the method to quantify the intensity as well as the volume and to determine 3.

(13) the. combinations. condition. of. training. the and. plyometric the. exercises. return-to-sport. for. both. phase. of. rehabilitation remain some space to discuss.. Previous researches had shown that the less the foot contact time spent, the more the explosive power and vertical jump. performance. obtained,. but. still,. there. were. no. quantification of foot contact time and rate (Horita et al., 2002;. Bobbert. et. al.,. 2004).. The. basic. components. of. pl yometric exercise are countermovement j ump, horizontal jump and depth j ump; therefore, previous studies had anal yzed the biomechanical parameters of these jumps in order to evaluate. the. intervention. sport of. performance. pl yometric. before. exercise. and. after. (Verhoshanski,. the 1969;. Verhoshanski & Tatyan, 1983; Hewett et al., 1996; Adams, 19 84 ; H ol c om b et al ., 19 9 6 ) . Ho w e v er, t h e s tu di e s o f t h e b ox drills were relatively rare.. Providing box drill was considered as a more complex pl yometric exercise according to the intensit y rank suggested by Chu (1998), the limited research on this topic evoked our interest to anal yz e certain biomechanical parameters of this form of jump to investigate the effect of different b ox jumps. The setting of the box jumps in the current study was based on C h u ’s p y r a m i d i n g b o x h o p s ( 1 9 9 8 ) . T h e j u m p d e s c r i p t i o n o f C h u ’s p y r a m i d i n g b o x h o p s w a s e n t i t l e d a s f r o n t t h e b o x ( F B ) 4.

(14) i n t h i s s t u d y, a n d a n o t h e r s i m i l a r j u m p w h i c h w a s m o r e l i k e t h e j u m p d e s c r i p t i o n o f H o u g l u m ’s m u l t i p l e j u m p s a n d h o p s ( 2 0 0 1 ) w a s e n t i t l e d a s c r o s s t h e b o x ( C B ) i n t h i s s t u d y.. Speed was suggested to be a means to adjust the intensity o f p l y o m e t r i c e x e r c i s e s ( H o u g l u m , 2 0 0 1 ) . N o r m a l l y, a t h l e t e s were instructed to complete the movements as fast as they c o u l d i n t h i s f o r m o f e x e r c i s e . T h e r e f o r e , i n t h i s s t u d y, different rates – 60 bpm, 75 bpm and 90 bpm were set to represent different speeds in order to investigate how the d i ff e r en t s p e ed s a ff e ct t h e h u m a n b o d y a n d t h e i n t e n s i t y.. 1.2 Purpose. The purpose of this study was to compare two box jumps and to investigate the effect of different jumping speeds toward. the. intensity. and. human. body. by. analyzing. the. biomechanical parameters of two box jumps (cross the box and front the box) and three different rates (60 bpm, 75 bpm and 90 bpm).. 5.

(15) Chapter 2 Literature Review. 2.1 Introduction of Plyometric exercise. Pl yometrics was originated from Europe simpl y referring to jump training. In the early 1970s, it was widely noticed according. to. the. splendid. performance. of. athletes. from. Eastern Europe in the sports of track and field, gym nastics, and. weight. lifting,. for. whom. jumping. exercises. were. imp l em e nt e d i n t h ei r t r ain in g p r o gr am s . H o w ev e r, t h e t e r m o f pl yometrics was firstl y coined by an American track and fiel d c o a ch n am e d F r e d Wilt . It s G r e e k o ri gi ns , pl io v e r su s m e tr i c, meant measurable enhancement (Houglum, 2001; Chu, 1992). Pl yometric exercises then rapidl y became popular to trainers and athletes for producing explosive power by linking force and speed together; it was considered to be essential to be included in the training protocols. especially for athletes. playing in jumpin g, weight lifting and throwing (Chu, 1992).. The ultimate goal of pl yometric exercises is to increase o u t p u t o f e x p l o s i v e p o w e r. I t s m e c h a n i s m w a s b a s e d o n t h e reaction. of. mechanical. and. neurological. components. neuromuscular system responding to the stress. in. (Houglum,. 2001). As for mechanical components, they could be divided into. contractile. elements. and 6. non -contractile. elements..

(16) Contractile elements are m yofibrils, while non -contractile elements were referred to series elastic component (SEC) and parallel. elastic. component. (PEC). according. to. their. a r r a n g e m e n t s . Te n d o n s a n d s h e a t h w e r e t h e m a i n c o n t r i b u t i o n s o f S E C a n d m u s c l e ’s c o n n e c t i v e t i s s u e s w e r e c l a s s i f i e d a s P E C . In. the. Stretch-. Shortening. Cycle. (SSC),. non-contractile. elements were deemed to be an important factor to power production. due. to. their. elastic. p r o p e r t y.. As. for. the. neurological components, muscle spindles and Golgi tendon organs play important roles in power output by activating the stretch reflex of muscle spindles and decreasing the inhibition from Golgi tendon organs. Therefore, plyometric exercise could be described as a means with the property of a quick eccentric. movement. followed. by. the. forceful. concentric. contraction to increase muscle strengt h and explosive power (Houglum, 2001; Chu, 1998).. There are three distinct phases in pl yometric exercises: eccentric. phase,. amortization. phase,. concentric. phase. (Houglum, 2001). In the eccentric phase, muscle is lengthened by a rapid stretch. Its mechanis m is due to muscle spindle is very sensitive to a sudden change in length of the muscle – the faster the rate of the stretch, the greater the amount of the response. This is the most important phase during plyometric exercises. since. facilitate. greater. they. could. response. increase of 7. muscle. the. stimulation. spindles. and. to. then.

(17) provide. greater. muscle. activities.. Amortization. phase. is. referred to the transition from eccentric phase to concentric phase. The amount of time of this phase should be kept short; otherwise the elastic energy gained from the last phase would be dissipated as heat and wasted. Also, the prolonged time in this phase would inhibit stretch reflex since the time and the force production are inversely related. Concentric phase is the outcome of the combined effect from eccentric phase and amortization phase. The desired explosive power would be produced in concentric phase if both eccentric phase and amortization phase could occur rapidly in a very short time. By integrating the mechanical and neurological components in neuromuscular system, pl yometric exercises could bridge the gap between muscle strength and forceful power output to imp r o ve sp o rt p e r f or m an c e (Wi lt , 1 97 5 ).. There are various types of plyometric exercises in lower extremities: jumps-in-place, standing jumps, multiple jumps and hops, box jumps and depth jumps (Figure 2.1-1 to Figure 2.1-5) (Houglum, 2001).. Jumps-in-place (Figure 2.1-1) are repeated jumps that involve jumping in the same place from the beginning to the end.. The. intensity. is. adjustable. from. low. to. high.. Jumps-in-place with low intensity are useful activities for establishing a short amortization phase and at the same time, 8.

(18) jump techniques could also be developed if these kinds of jumps relate to the specific sp orts (Houglum, 2001).. Figure 2.1-1. Jumps-in-place Not e. From T herapeuti c Exerci s e f o r At hl eti c In ju ri es ( p . 2 9 9 ) , b y P. A . H o u g l u m , 2 0 0 1 , C h a m p a i g n , I L : H u m a n Kinetics. Copyright 2001 by Peggy A. Houglum.. Standing jumps (Figure 2.1-2) are single jumps that put emphasis on maximal effort for each exertion; therefore the recovery time between jumps is exceptionally crucial. The direction of its motion could be either horizontal or vertical. The intensity could progress by adding barriers such as con es and advance by including sprint immediately after landing (Houglum, 2001).. 9.

(19) Figure 2.1-2. Standing jumps Not e. From T herapeuti c Exerci s e f o r At hl eti c In ju ri es ( p . 3 0 0 ) , b y P. A . H o u g l u m , 2 0 0 1 , C h a m p a i g n , I L : H u m a n Kinetics. Copyright 2001 by Peggy A. Houglum.. Multiple jumps and hops (Figure 2.1-3) require the skills from both jumps -in-place and standing jumps. These t ypes of jumps address on maximal attempts without resting between repetitions. The intensity could be modified by performing the jumps with one or two legs, with or without barriers, in a single or multiple directions (Houglum, 2001).. Figure 2.1-3. Multiple jumps and hops Not e. From T herapeuti c Exerci s e f o r At hl eti c In ju ri es ( p . 3 0 2 ) , b y P. A . H o u g l u m , 2 0 0 1 , C h a m p a i g n , I L : H u m a n Kinetics. Copyright 2001 by Peggy A. Houglum. 10.

(20) Box jumps (Figure 2.1-4) involve jumps and hops on and off. boxes. with. various. heights. that. they. require. more. advanced skills from multiple jumps and hops. The directions include both vertical and horizontal jumps. The inte nsity depends on the box height. The number of the box could be set from one to five (Houglum, 2001; Chu, 1998).. Figure 2.1-4. Box jumps Not e. From T herapeuti c Exerci s e f o r At hl eti c In ju ri es ( p . 3 0 6 ) , b y P. A . H o u g l u m , 2 0 0 1 , C h a m p a i g n , I L : H u m a n Kinetics. Copyright 2001 by Peggy A. Houglum.. Depth jumps (Figure 2.1-5) are considered to be the most a g g r e s s i v e j u m p s a m o n g a l l b e c a u s e s u b j e c t ’s o w n w e i g h t a n d the. acceleration. of. gravity. are. involved. additionally. s i m u l t a n e o u s l y. T h e m o v e m e n t d e s c r i p t i o n o f t h e s e k i n d o f jumps is first to step off the box, seco nd drop on the ground, third jump upward off the ground immediately with maximal exertion. There is one thing should be kept in mind that the first move is to step off the box instead of jump off the box therefore extra stresses could be avoided. The inten sity could 11.

(21) be. progressed. by. landing. and. jumping. with. single. increasing box height and box numbers (Houglum, 2001).. Figure 2.1-5. Depth jumps Not e. From T herapeuti c Exerci s e f o r At hl eti c In ju ri es ( p . 3 0 8 ) , b y P. A . H o u g l u m , 2 0 0 1 , C h a m p a i g n , I L : H u m a n Kinetics. Copyright 2001 by Peggy A. Houglum.. 12. leg,.

(22) 2 . 2 Tr a i n i n g P l a n o f P l y o m e t r i c e x e r c i s e. Before implementing pl yometric exercise into training protocols, there are three prerequisite parameters need to be noted;. they. are. strength,. f l e x i b i l i t y,. and. proprioception. (Houglum, 2001; Chu, 1998).. According to the definition of power – rate of work production, that can also be expressed as the product of force and. velocit y;. greater. force. would. produce. greater. power. which is the reason why muscle strength is regarded as the foundation of the pl yometric exercises. Enough strength could assure better quality of the movement control required in the pl yometric exercises and also it could reduce the incidence of injuries from overuse. Besides, while the difficulty of the pl yometric exercises progress es, the greater strength may be needed.. Another. benefit. from. strengthening. is. that. the. hypertrophied muscles provide additional elastic elements in the eccentric phase due to their increased cross sections to provide greater strength. Submaximal pl yometric exercises such as skipping could be applied at the first beginning; h o w e v e r, t h e m i n i m u m s t r e n g t h r e q u i r e d f o r t h e p l yo m e t r i c exercises depends on the severity on demand (Houglum, 2001). Squat with 60 % body weight five times within five seconds was. recommended. by. Chu. (1998). for. pl yometric exercis es in lower extremities. 13. more. demanding.

(23) Power generated from concentric phase also relies on the amounts of lengthening of the muscles during the eccentric phase of pl yometric exercises. Therefore, muscles with better flexibility allow better degree of lengthening and then result in greater power production. Besides, muscles with good flexibility not only provide full ROM needed for activities but also provide a better level of force absorption in plyometric exercises that were known as exercises with high impacts and stresses (Houglum, 2001).. Proprioception is. referred. to. the. ability of. body to. transmit position sense as well as kinesthesia, to discriminate the. information. consciously. or. and. then. to. respond. unconsciously. to. to. the. stimulation. regulate. the. posture. or. m o v e m e n t o f t h e b o d y a p p r o p r i a t e l y. G o o d a t h l e t i c s k i l l s r e l y on good proprioception and proprioception could also be p r e s e n t e d a s a g i l i t y,. balance. and. coordination. (Houglum,. 2001). Therefore, it is not so hard to understand that why a c e r t a i n d e g r e e o f a g i l i t y, b a l a n c e a n d c o o r d i n a t i o n i s r e q u i r e d in. plyometric. exercises. to. adequately. perform. controlled. forceful and rapid movements. Although different severity and complexity of plyometric exercises require different levels of c o n t r o l , a g i l i t y, b a l a n c e a n d c o o r d i n a t i o n a r e n e e d e d i n a l l levels of pl yometric activities. For this reason, any t ypes of pl yometric exercises should be avoided before basic static and dynamic proprioception could be acquired. (Houglum, 2001; 14.

(24) Zamani, Rahnama, Khayambashi, & Lenjannezhad , 2010).. As. to. design. plyometric. programme,. there. are. four. v a r i a b l e s c o u l d b e m a n i p u l a t e d ; t h e y a r e i n t e n s i t y, v o l u m e , frequency. and. recovery. (Houglum,. 2001;. Chu,. 1998;. Allerheiligen & Rogers, 1995).. Intensity is the degree of effort involved in doing an exercise. or. exercises, complexity. the. stress. intensity of. the. of. the. given. could. be. adjusted. task,. adding. task.. weights. by. In. plyometric. changing. during. the. the task,. increasing the speed of the task, raising the height of the boxes or increasing the distance covered (Houglum, 2001; Chu, 1998).. Vo l u m e i s t h e t o t a l w o r k e x e c u t e d i n a s i n g l e s e s s i o n . I n lower extremities, the volume of the pl yometric exercises is monitored by the numbers of foot contact in jumping tasks and by distance in bounding tasks duri ng one session. In upper extremities,. the. volume. of. the. pl yometric. exercises. is. measured by the numbers of repetition. The intensity and the goals would help to determine the appropriate volume selected in any plyometric exercise session (Houglum, 2001; Chu, 1998).. Frequency is the number of times/sessions that are taken 15.

(25) place in a training cycle. Though it also depends on the intensity of the exercise and the tolerance of the individual, at least forty-eight hours between sessions is recommended (Houglum, 2001; Chu, 1998).. Recovery is referred to the quantity of resting time between sets or groupings of multiple exercises. It is the key factor to determine the pl yometric exercises applied focus on developing the power or enhancing the muscular endurance (Houglum, 2001). Generally speaking, shorter resting time (10 to 15 seconds) between sets is used to promote muscular endurance, while longer resting time (45 to 60 seconds) between. sets. is. used. to. improve. power. (Chu,1998).. A c c o r d i n g l y, a w o r k t o r e s t r a t i o o f 1 : 5 t o 1 : 1 0 w a s s u g g e s t e d to assure the intensity of the exercise and the adequate performance (Chu, 1998).. There are some other issues need to be considered before starting. pl yometric. exercises. as. they. are. normally. more. intense than other forms of exercise programs. These issues include age, body weight, competitive level, surface, foot wear, technique, progression, goals (Houglum, 2001; Chu, 1998; Allerheiligen & Rogers, 1995).. Pl yometric. exercises. should. be. applied. carefully. on. children and youth (8 to 13 years old) due to their physical 16.

(26) immaturity – their bones and muscles are not strong enough to bear the stress and the mechanism of their proprioceptive feedback is not fully mature yet to cope with the intense activities. pl yometric. Thus,. the. exercises. volume should. and be. the. kept. intensity l o w.. The. of. the. general. guideline is that moderate to high intensity should be avoided for those under the age of sixteen (Houglum, 2001).. Pl yometric exercises are activities of high impact, so naturally they would impose more stress on joints and tendons. For those whose body weight is 100Kg or above could not perform the same pl yometric exercises as those who with lighter body weight due to safety consideration (Allerheiligen & Rogers, 1995).. Competitive. level. determines. the. training. level. of. pl yometric exercises appl ied in the therapeutic program s. That is to say all the therapeutic program s should involve a c e rt a in l e v el o f p l yo m et r i c ex e r ci s e s, h o w ev e r, mo d e r at e - t o high- level plyometric exercises are likely to be executed on those who participate in competitive sports while the same intensity level for competitive athletes may not be required for those who with recreational purpose (Houglum, 2001).. The. proper. surface. for. implementing. pl yometric. exercises is that neither too hard nor too soft, and with the 17.

(27) ability to absorb some of the impacts come from plyometric tasks. The appropriate surface, for example, Resilite mats are good for the indoor activities and grass is good for the outdoor exercises. Harder surface like concrete should be avoided because of the higher impact forces . The reason why softer surface is not very adequate is that it would result in reducing the elastic propert y needed in pl yometric exercises (Houglum, 2001; Chu, 1998). Shoes with good cushion and support are the best footwear for plyometric exercises. Again, i f t h e s h o e i s t o o s p o n g y, i t w o u l d c a u s e t h e i n s t a b i l i t y a t landing. and. take-off. during. the. activities,. thus. a. good. execution would be restricted (Houglum, 2001).. Proper. technique. is. very. important. for. performing. pl yometric exercises. It is suggested to land with midfoot and then push-off with the ball of foot in order to decrease the imp acts an d to red u ce t h e amo rtiz at i on p h as e. Tru nk s ho ul d b e kept. straight. so. forces. could. be. transmitted. and. the. contribution of arms could be utilized. The quality of the performance needs to be monitored and fatigue should be p r e v e n t e d ; i n t h i s w a y, u n d e s i r e d m o v e m e n t s , b a d h a b i t s a n d risk. of. injury. minimized. during. (Houglum,. the. pl yom etric. 2001).. The. exercises. progression. could. be. depends. on. i n d i v i d u a l ’s p h y s i c a l c o n d i t i o n a n d t h e a d a p t a t i o n s t o t h e stress.. Lower. level. tasks. should. be. accomplished. before. moving to the next stage. The means of progression include 18.

(28) a d j u s t i n g t h e i n t e n s i t y, r e s t i n g t i m e a n d t h e d u r a t i o n o f t h e given tasks (Houglum, 2001). Goal settings are determined by i n d i v i d u a l ’s. condition. and. the. sport. participati on.. They. s h o u l d a l s o b e e v a l u a t e d a n d r e - e v a l u a t e d b y i n d i v i d u a l ’s performance to match their progressions. While the current goals are achieved, new goals should be established (Houglum, 2001).. 19.

(29) 2.3 Adaptations after Plyometric exercise. There were many previous studies proved that after the intervention. of. improvements. pl yometric in. lower. exercises,. extremities. various could. significant. be. observed. i n c l u d i n g m o t o r s t r a t e g i e s , m o t o r c o n t r o l s , j o i n t s t a b i l i t y, sport injury prevention and anaerobic power output .. As. for. motor. strategies. and. motor. controls,. motor. strategies learnt in pl yometric program s could be reproduced during. the. activities,. such. as. quadriceps -hamstrings. co-activation and adductors pre-activation to provide knee stability. (Chimera. pl yometric. exercises. et. al.,. into. 2004).. the. Also,. regular. implementing. endurance. training. programs of some triathletes who were suffer ing from the aberrant. neuromotor. control. during. running. after. cycling. could hold a positive outcome in correcting the aberrance (Bon acci , 20 11 ).. Knee and ankle injuries were common to see in sport field ; h o w e v e r, p r e v i o u s s t u d i e s s h o w e d t h a t b o t h o f t h e j o i n t s c o u l d benefit from pl yometric exercises in various ways. Chimera et al. (2004) suggested that knee stability could be increased after the intervention of pl yometric exercises. Heweet et al . (1996) found that after implementing plyometric exercises into a training program could efficiently decrease the impact 20.

(30) forces during landing and could reduce adduction/abduction torque of the knee joint to lessen the incidence of non -contact ACL injury in female athletes. There were also meaningful changes found in Lower Extremity Functional Scale, Knee O u t c o m e S u r v e y, a g i l i t y t e s t , v e r t i c a l j u m p p e r f o r m a n c e , a n d 40-yard sprint test after the intervention of both plyometric and agility trainings for patient with post -surgical anterior knee pain in a case report (Newberry & Bishop, 2006). A knee proprioception assessment was conducted by Zamani et al. in 2010 by asking subjects to reproduce three fixed knee angles and by using Biodex isokinetic dynamometer to calculate the proprioception. senses;. significant. improvements. were. observed in the group that included an eight-week plyometric training. Ismail et al. (2010) investigated the effect of both pl yometric exercises and resistive exercises for athletes after inversion. ankle. sprain.. They. found. that. functional. performance was better improved in pl yometric group than in resistive group after six week respective training.. One. of the most. important. effects desired after. the. intervention of pl yometric exercises is the explosive power which was proved to be enhanced by Luebbers et al. (2003). H o w e v e r, a c c o r d i n g t o t h e i r f i n d i n g s , t h e s u ff i c i e n t t i m e o f recovery should be applied to the trainings with high volumes and short sessions, otherwise the desired optimal performance would be affected. 21.

(31) 2.4 Plyometric exercise & Resistance training. Anterior cruciate ligament (ACL) injury is not uncommon for athletes in sport field. Therefore, there are various ACL prevention programs established in order to reduce the risk of t h e i n j u r i e s . N o r m a l l y, A C L p r e v e n t i o n p r o g r a m s a r e t h e combinations of several training protocols such as flexibility exercise, training. resistance and. training,. plyometric. balance. exercise.. training,. The. training. agility. protocols. mentioned above were proved to be effective in decreasing the incidence of AC L injury (Rozzi et al., 1999; Caraffa et al., 1996).. H o w e v er,. there. seemed. to. be. a. tendency. for. the. researchers to compare the effects of pl yometric exercise versus resistance training before and after the interventions via. investigating. their. changes. in. n euromuscular. and. biomechanical characteristics.. As for the difference between plyometric exercise and resistance training, several variables were always discussed in previous studies such as the incidence of non -contact ACL i n j u r y, q u a d r i c e p s s t r e n g t h , h a m s t r i n g s t o r q u e , j o i n t a n g l e s o f hip flexion and knee flexion during landing, pre -activation of h i p a b d u c t o r , c o - a c t i v a t i o n o f h i p a d d u c t o r a n d a b d u c t o r, a n d ground reaction force (GRF).. Non-contact ACL injury was claimed to be reduced in 22.

(32) both pl yometric exercise and resistance training. Lehnhard et al. (1996) declared that athletes could benefit from regular s t r e n g t h e n i n g t o d e c r e a s e t h e i n c i d e n c e o f A C L i n j u r y. H e w e t t et. al.. (1996). also. suggested. after. the. intervention. of. pl yometric exercise for eight w eeks, non-contact ACL injury of female athletes would be reduced.. As. for. quadriceps. strength. and. hamstring. torque,. significant improvements of quadriceps strength were both found in plyometric exercise and resistance training ( Lephart et al . , 2 00 5 ). H o w ev e r, h a ms tr in g s to r qu e w as on l y f o u n d ameliorated. after. pl yometric. intervention. (Hewett. et. al.,. 1996).. Joint angles of hip flexion and knee flexion during landing task were thought to be an important variable to assess because joint forces during the landing task could be attenuated and hamstrings would also be tensioned to protect ACL with the additional posterior force (Renstrom et al.,1986 ; Hirokawa et al.,1991). Lephart et al. (2005) suggested that the desired increase of hip flexion and knee flexi on during the jump-landing task could be observed in both plyometric and basic resistance groups.. The activations of hip adductor/abductor were only found in plyometric group (Lephart et al., 2005). The preparatory 23.

(33) activation of gluteus medius was observed before landing in his study, thus, thigh was thought to be positioned in advance to cope with the impact forces at landing which may lead to inappropriate hip adduction and knee valgus (Zeller et al., 2003; Ferber et al., 2003). Similar, the increase of early co-activation of hip adductor and abductor was reported in Chimera’s. study. (2004). after. a. six -week. intervention. of. pl yometric exercises.. In addition, both Hewett et al. (1996) and Irmischer et al. (2004) reported that a reduction of ground reaction force (GRF) was observed after including plyometric exercises into training protocols. For the standpoint of injury prevention, it is important to decrease vertical GRF during jump -landing task due to the notion that the less impact forces upon the joints, the lower onsets of the injuries.. 24.

(34) 2.5 Clinical application of Plyometric exercise. Pl yometric exercises were first used to enhance explosive power and improve sport performance for uninjured athletes , and yet in recent years, they are usually cooperated into rehabilitation programs for post-injured athletes in order to help. them. traditional. safely. return. therapeutic. to. sports. exercises. participation s.. address. more. on. The the. t r e a t m e n t s o f t h e e a r l y s t a g e a f t e r i n j u r y, f o r e x a m p l e i t i s strongly recommended to start with a relatively slower speed, to begin with lower forces and to initiate movements at single planes. in. order. to. facilitate. desired. neuromuscular. recruitment, to regain full ROM, to increase muscle strength and to enhance muscle endurance (Kannus Parkkari & Jarvinen, 20 03 ; S a al , 19 91 ) ; h ow e v e r, t ho s e c ou ld h a rd l y s i m ul at e th e real demands of forces, speed, movements and techniques required. in. athletic. competitions.. Therefore,. plyometr ic. exercise could be regarded as a crucial training protocol to be included in the therapeutic exercises for those who need to return to athletic competitions or high-demanding activities; furthermore, it could also be used as a means to evaluate that if the athletes are ready to return to play (Newberry & Bishop, 2006; Gregory et l., 2008).. Another important thing to keep in mind is even the lowest intensity of plyometric exercise s should be avoided in 25.

(35) several. occasions,. for. example,. the. early. stage. of. rehabilitation, the acute stage after injury or the stage of consisting pain and remaining joint instability (Wilk et al., 1993). It is very crucial for participants to obtain a certain muscle. strength,. neuromuscular. control. f l e x i b i l i t y, before. proprioception implementing. and. plyometric. exercises as a part of rehabilitation program s. Generally speaking, it is applied in the late stage of rehabilitation and should be combined with sport-specific trainings.. 26.

(36) Chapter 3 Material and Methods. 3.1 Subjects. Tw e l v e h e a l t h y, m a l e a t h l e t e s w e r e r e c r u i t e d f r o m t r a c k a n d f i e l d t e a m i n N a t i o n a l Ta i w a n U n i v e r s i t y o f P h y s i c a l Education and Sport. Their specialties were high jump and long jump. Subjects reported no history of serious knee injury or other lower extremity trauma within 6 months. All subjects participated in nationally or locally organized track and field competitions and they had regular training programs including weight training, endurance, speed, agility and plyometric exercise. This study was approved by the Research Ethics Committee of the Central Regional Research Ethics Center (Appendix C) and all the subjects provided written informed consent (Appendix B) prior to their participations. All of them were able to follow the instructions and complete the movements demanded in this experiment without any problem. The basic information of these twelve subjects in this study w a s s h o w n i n Ta b l e 3 . 1 .. Tabl e 3. 1. Subject information (Mean±SD) Age (y/o). Height (cm). Body mass (Kg). 21± 2. 178± 8. 70± 6 27. Track & field experience (year) 9± 4.

(37) 3.2 Experimental Instrumentation. VICON. motion. anal ysis. system,. two. Kistler. force. p l a t e f o r m s w e r e u s e d f o r d a t a c o l l e c t i o n i n t h i s s t u d y. T h e laboratory setting was shown in Figure 3.2-1.. Figure 3.2-1. Laboratory setting. 3.2.1 Motion analysis system VICON motion anal ysis system (Oxford Metrics LID. UK) (Figure 3.2-2) with eight high-speed optical cameras (Figure 3.2-2) was used to collect kinematical data.. 28.

(38) Fi gure 3 . 2-2 . V IC ON mo ti on an al ys is s ys t em. 3.2.2 Force plateform Kinetic. data. were. collected. using. two. Kistler. force. plateforms (Type 9260AA6, Swiss) (Figure 3.2-3).. Fi gure 3 . 2-3 . Ki st ler fo rce pl at efo rm. 3.2.3 Plyometric box The heights of the pl yometric boxes in this study were 20 c m , 3 0 c m a n d 4 0 c m r e s p e c t i v e l y, n o n s l i p s u r f a c e s w e r e attached on the top of the box es. Width x length was 30 cm x 40 cm for each box. The gaps between two boxes of same 29.

(39) heights were 5.5 cm and the distances between two boxes of different heights were 62.5 cm (Figure 3.2-4).. 5.5 cm 62.5 cm. 62.5 cm. Fi gure 3 . 2-4 . P l yom et ri c box. 30.

(40) 3.3 Experimental Procedure s. Instrumentation set-up. System Calibration. written consent. Anthropometry collection. Subject warm-up. Marker set attachment. Static data collection. Dynamic data collection. Data anlysis and processing Figure 3.3-1. Experimental procedures 31.

(41) 3.3.1 Instrumentation set-up Eight high speed optical cameras were set surrounded two Kistler force plateforms. The sampling rate of the high speed cameras was 250 Hz that the three-dimensional trajectories of the marker sets on the subject could be captured. And all the markers should be captured by at least two cameras. VICON NEXUS software was utilized to label the markers and process the data collected.. Tw o K i s t l e r f o r c e p l a t e f o r m s w e r e s e t b e t w e e n 3 0 c m a n d 4 0 c m b o x e s b i l a t e r a l l y. G r o u n d r e a c t i o n f o r c e s a n d m o m e n t s were sampled at a rate of 1000 Hz during plyometric box jump.. 3.3.2 System Calibration A wand (Figure 3.3-2) was used to calibrate the capture volume and the error correction of the cameras. An L -frame (Figure 3.3-3) was set to define the laboratory coordinate system.. F i g u r e 3 . 3 - 2 . Wa n d. 32.

(42) Fi gure 3 . 3-3 . L-fr am e. 3.3.3 Collection of Anthropometric data Linear and circumferential anthropometric measurements of each subject were recorded before the experiment for later data processing (Appendix A). The segments we measured including upper arms, forearms, torso, pelvis, thighs and lower legs.. 3 . 3 . 4 Wa r m - u p Each subject had 5 to 10 minutes to warm up which was arranged to reduce the risk of injury and to decrease the fatigue during the pl yometric box jumps performed in the experiment. The warm-up exercises contained light flexibility exercises such as light stretching of flexors and extensors in hip, knee and ankle joint, and included light skipping and bouncing.. 3.3.5 Marker set attachment The marker set was attached on the anatomical landmarks of the subjects to represent the three -dimensional trajectory of. each. body segment.. The. markers 33. were. placed. on. the.

(43) anatomical. landmarks. modified. from. Helen. Hayes. ( Ta b l e. 3.3-1).. Ta b l e 3 . 3 - 1 . Marker set attachments L/ R Anatomical landmarks. Note side. Pelvis. ASIS. L & R. -. PSIS. L & R. -. -. Share the same horizontal. Sacrum. plane with ASIS and PSIS. L/E. GT. L & R. -. Medial knee. L & R. -. Lateral knee. L & R. -. Medial malleolus. L & R. -. Lateral. L & R. -. 2nd metatarsal. L & R. -. Calcaneus. L & R. Share the same horizontal. malleolus. plane with 2nd metatarsal.. N o t e . L / E : L o w e r e x t r e m i t y, A S I S : A n t e r i o r s u p e r i o r i l i a c s p i n e , P S I S : P o s t e r i o r s u p e r i o r i l i a c s p i n e , G T: G r e a t e r Tr o c h a n t e r,. M e d i a l k n e e : M e d i a l e p i c o n d yl e o f f e m u r, La t e r a l k n e e : L a t e r a l e p i c o n d y l e o f f e m u r. L : L e f t , R : R i g h t .. 3.3.6 Data collection of neutral posture Subject. stood. statically. with 34. the. neutral. position..

(44) Articulation centers and relative distances collected between joints in this stage could be used as the basic information for calculation in dynamic data anal ysis and as the reference for dynamic movements .. 3.3.7 Dynamic data collection The jumping rates of this study were 60 bpm, 75 bpm and 9 0 b p m r e s p e c t i v e l y. T h e s u b j e c t s w e r e f i r s t s t a n d i n g w i t h feet shoulder-width apart and then instructed to jump cross the box (CB) (Figure 3.3-4) or front the box (FB) (Figure 3 . 3 - 5 ) w i t h t h e r a t e s m e n t i o n e d a b o v e i n a r a n d o m i z e d o r d e r. CB referred to the subjects jump over the box that there were only three foot contacts while completing the jump ; this form of jump was similar to multiple jumps and hops described by Houglum (2001). FB meant subjects jump up to the box and down to the ground consecutively for three times ; this form of jump was based on the pyramiding box hops described by Chu (1998). There were six sets of box jumps with corresponding rates and each set contained three trials. Subjects had at least two minutes break between sets to prevent fatigue. Plyometric boxes and force plates were placed bilaterally as shown on Figure 3.3-6.. 35.

(45) 62.5 cm. 62.5 cm. 5.5 cm. Fi gure 3 . 3-4 . Cross t he box. 62.5 cm. 5.5 cm. 62.5 cm. Fi gure 3 . 3-5 . Front t he box. 36.

(46) 40 cm 30 cm. 20 cm. Fi gure 3 . 3-6 . P l yom et ri c box es and fo rce p l at e fo rms. 3.3.8 Data processing and analysis Human segments were assumed to be the rigid body in this. s t u d y.. High. speed. cameras. were. set. to. capture. the. three-dimensional trajectories of the reflective markers in space and the coordinate system of all the segments would be defined. smoothed. The by. trajectories. of. 6. pass. cross-validation. Hz. low. spline. the. reflective. filter. smoothing. markers. through. route. were. generalized. ( Wo l t r i n g ,. 1986).. Joint centers could be marked and calculated by the reflective markers attached on subjects. Real pos ition of the mass center for. each. segment. could. be. deducted. by. Anthropometry. measurements and relative position of mass centers for each segment (de Leva, 1996), so the acceleration of center of gravity. and. Euler. parameters. of. each. segment. in. the. laborator y coordinate system would then be obtained. Joint angles could be calculated by Euler angle and the rotatory 37.

(47) orientation was defined as following: flexion/extension (y) abduction/adduction. (x’ ). -. internal. rotation/external. rotation (z” ). The mass of each segment and the moment of inertia. of. each. segment. were. calculated. by. McConville. formula (1980). Joint forces and joint moments were obtained by newton-Euler equation through inverse dynamic methods.. As for joint Kinematics and Kinetics, the second jump was extracted from one complete box jump to represent the Kinematics and Kinetics patterns. It could be divided into five checkpoints by the lines of the time frames on horizontal axis. These checkpoints were (1)landing, (2)peak landing force, (3)maximum knee flexion, (4)take-off after landing, (5)last maximum jumping height. The joint angles of hip joint and knee joint at landing as well as maximum knee flexion were important indicators for researchers to speculate the amounts of impact forces attenuation upon joints. Peak landing force and time to peak landing force were parameters for rate of force d ev el op m en t cal cu l at io n. Tim e t o m ax i mu m k n ee fl ex i o n was also an indicator to speculate the impact force absorption for the joints. The time from landing to take -off was the total foot contact which was an important factor for researchers to evaluate the effect of stretch -shortening cycle (SSC).. 3.3.9 Statistical analysis D a t a w e r e a n a l y z e d w i t h S P S S 1 2 . 0 . Tw o - w a y ( 2 b o x 38.

(48) jumps. x. 3. velocities). repeated. measures. A N O VA. were. performed to access the differences in kinetic and kinematic al parameters. Statistical significance of p <.05 was set.. 39.

(49) Chapter 4 Results. In. this. s t u d y,. we. assume. that. box. jumping. is. a. symmetrical movement. In this case, ROM, joint forces and joint moments are considered to be equal bilaterally during box jump, therefore the following results presented are the biomechanical analysis of the data from subjects’ dominant legs which were declared to be right.. 4.1 Joint Kinemati cs & Kinetics during Different Box Jumps. The patterns of Kinematics and Kinetics during different box jumps were showed in Figure 4.1-1 to Figure 4.1-6.. In Figure 4.1-1, while performing CB, hip joint was about 30 degrees at landing and then the angle of flexion kept increased and reached its peak at the point of maximum knee flexion which was about 67 degrees. After that, hip joint s t a r t e d t o e x t e n d t o t h e c h e c k p o i n t o f t a k e - o f f a n d a f t e r. A t the point of last maximum jumping height , hip flexed around 71 degrees. Furthermore, hip joint remained slight abduction and external rotation throughout the jump. As for hip joint moment, between the checkpoints of landing and peak landing force, hip flexor reached its peak moment and hip exten sor 40.

(50) reached its peak moment at around 0.008 seconds after the checkpoint of peak landing force. Then hip extensor worked as the prime mover until the checkpoint of take -off. Hip abductor activated before landing but adductor worked between the checkpoint of landing and maximum knee flexion. After that, hip abductor activated again until the checkpoint of take -off. As for hip joint force, a great compression force took place right after the checkpoint of peak landing force. Also, there was. a. slight. anterior. shear. force. observed. between. the. checkpoint of landing and peak landing force, while peak posterior shear force took place right after the checkpoint of peak landing force and then carried out to take -off. Peak medial shear force was noted as the point tha t peak posterior shear force occurred.. 41.

(51) Fi gure 4 . 1-1 . Hip joi nt an gl e, j oi nt mom ent and j oi nt force o f cross the box (CB) during box jump. Note. Checkpoints: (1)landing (2)peak landing force (3)maximum knee flexion (4)take-off after landing (5)last maximum jumping height. 42.

(52) In Figure 4.1-2, while performing FB, hip joint was about 20 degrees at landing and then the angle of flexion kept increased and reached its peak at the point of maximum knee flexion which was about 68 degrees. After that, hip joint extended to the checkpoint of take-off. At the point of last maximum jumping height, hip flexed around 12 degrees. Also, hip joint remained abduction and external rotation throughout the jump. As for hip joint moment, after 0.02 seconds of landing, hip flexor reached its peak moment and then hip extensor activated rapidly before. the checkpoint of peak. landing force. Hip flexor reached its second peak at 0.008 seconds after the checkpoint of peak landing force , then again hip. extensor. activated. rapidly. to. its. peak. around. 0.028. seconds after the checkpoint of peak landing force. After that, hip extensor worked until take-off. Hip abductor activated before landing but adductor worked through the jump. Hip external rotation moment was foun d through the same period of time. As for hip joint force, FB was like CB. A great compression force was notable right after the checkpoint of peak landing force. There was also a slight anterior shear force observed between the checkpoint of landing and peak landing force, while peak posterior shear force took place right after the checkpoint of peak landing force and then carried out to take-off. Peak medial shear force was noted as the point that peak posterior shear force occurred.. 43.

(53) Fi gure 4 . 1-2 . Hip joi nt an gl e, j oi nt mom ent and j oi nt force o f front the box (FB) during box jump . Note. Checkpoints: (1)landing (2)peak landing force (3)maximum knee flexion (4)take -off after landing (5)last maximum jumping height. 44.

(54) In Figure 4.1-3, while performing CB, knee flexion was around 23 degrees at landing and increased to its peak value of 76 degrees at the checkpoint of maximum knee flexion; after that knee then extended to the checkpoint of take -off. At the point of last maximum jumping height, knee flexed around 112 d egrees . As fo r k n ee jo in t mom ent , th e p ri me m ov er between. landing. and. take -off. was. knee. e x t e n s o r.. Knee. adduction moment was found throughout the same period of time. as. knee. e x t e n s o r.. And. there. was. not. much. of. internal/external rotation moment during the jump. As for knee joint force, a great compression force took place right after the checkpoint of peak landing force. The main joint force in knee joint. during landing and take -off was the. anterior shear force. Medial shear force also took place from landing to take-off.. 45.

(55) Fi gure 4 . 1-3 . Knee j oi nt an gl e, jo in t m om ent and j oi n t force of cross the box (CB) during box jump . Note. Checkpoints: (1)landing (2)peak landing force (3)maximum knee flexion (4)take -off after landing (5)last maximum jumping height. 46.

(56) In Figure 4.1-4, while performing FB, knee flexion was around 19 degrees at landing and increased to its peak value of 81 degrees at the checkpoint of maximum knee flexion; after that knee then extended to the checkpoint of take -off. At the point of last maximum jumping height, knee flexed around 30 degrees. As for knee joint moment, the prime mover b e t w e e n l a n d i n g a n d t a k e - o f f w a s k n e e e x t e n s o r. H o w e v e r, between the checkpoints of landing and peak landing force, knee extensor activated right after landing, and then knee f l e x o r t o o k p l a c e r a p i d l y a f t e r. A f t e r k n e e e x t e n s o r r e a c h e d its peak moment which is around 0.008 seconds after the checkpoint of peaking landing force, knee extensor activated throughout the jump until take -off. Knee adduction moment was notable from landing to take-off, and same as knee internal rotation moment. As for knee joint force, FB was similar to CB. A great compression force was found right after the checkpoint of peak landing force. Medial shear force took place from landing to take -off. Besides, the main joint force during landing and take -off was the anterior shear force.. 47.

(57) Fi gure 4 . 1-4 . Knee j oi nt an gl e, jo in t m om ent and j oi n t force of front the box (FB) during box jump . Note. Checkpoints: (1)landing (2)peak landing force (3)maximum knee flexion (4)take -off after landing (5)last maximum jumping height. 48.

(58) In Figure 4.1-5, while performing CB, ankle joint landed with planar flexion 25 degrees which decreased through the foot contact on the force plate; dorsiflexion slightly increased after the point of maximum knee flexion, then plantar flexion i n c r e a s e d a g a i n t o t h e c h e c k p o i n t o f t a k e - o ff a n d a f t e r. A s f o r ankle joint moment, plantar flexor took place from landing to take-off. Ankle invertor activated before the check point of maximum knee flexion, and ankle evertor took over after that. Ankle external rotation moment was also noted from lan ding to take-off. As for ankle joint force, a great compression force was found right after the checkpoint of peak landing force. The main joint force in ankle joint during landing and take -off was the anterior shear force. And lateral shear force was notable around the checkpoint of peak landing force.. 49.

(59) Fi gure 4 . 1-5 . Ankle j oi nt an gl e, j oi nt m om ent an d jo i nt fo rce of cross the box (CB) during box jump . Note. Checkpoints: (1)landing (2)peak landing force (3)maximum knee flexion (4)take -off after landing (5)last maximum jumping height. 50.

(60) In Figure 4.1-6, while performing FB, ankle joint landed with planar flexion 24 degrees which decreased through the foot contact on the force plate; dorsiflexion slightly increased after the checkpoint of maximum knee flexion, then plantar f l e x i o n i n c r e a s e d a g a i n t o t h e c h e c k p o i n t o f t a k e - o ff a n d a f t e r. As for ankle joint moment, plantar flexor took place from landing to take-off. Ankle plantar flexor reached to its first peak moment around 0.008 seconds after the checkpoint of peak landing force and reached to its second peak around 0.08 s e c o n d s b e f o r e t a k e - o f f r e s p e c t i v e l y. A n k l e i n v e r t o r a c t i v a t e d from landing to take-off. Ankle internal rotation moment was also noted from landing to take -off. As for ankle joint force, FB and CB were alike. A great compression force was notable right after the checkpoint of peak landing force. Lateral shear force was also found around the checkpoint of peak landing force. And the main joint force during landing and take -off was the anterior shear force.. 51.

(61) Fi gure 4 . 1-6 . Ankle j oi nt an gl e, j oi nt m om ent an d jo i nt fo rce of front the box (FB) during box jump . Note. Checkpoints: (1)landing (2)peak landing force (3)maximum knee flexion (4)take -off after landing (5)last maximum jumping height. 52.

(62) The time parameter of the joint kinematics was also i n c l u d e d i n t h i s s t u d y. T i m e t o m a x i m u m k n e e f l e x i o n ( F i g u r e 4.1-7) and total foot contact time (Figure 4.1 -8) were calculated. Although the subjects in the current study had to follow the rates instructed instead of their maximal exertions while performing box jumps, it still gave us a glimpse of how the different rates result in different foot contact time. Different box jumps were found no significant differences in t i m e t o m a x i m u m k n e e f l e x i o n u n d e r e a c h r a t e ; h o w e v e r, t h e r e was a tendency found for FB to hold longer time to maximum knee flexion than CB. As for total foot contact time, FB was gr e a t e r th a n C B a t t h e r a t e o f 6 0 b pm an d 7 5 bp m; h ow e v e r, when it comes to 90 bpm, two jumps showed no signific ant difference.. 53.

(63) Fi gu re 4. 1 -7 . Tim e t o m ax i mu m k n ee fl ex i on o f di fferent box jumps under different rates . Note. *p < .05. bpm: beat per minute, CB: cross the box, FB: front the box.. F i g u r e 4 . 1 - 8 . To t a l f o o t c o n t a c t t i m e o f d i f f e r e n t b o x j u m p s under different rates . Note. *p < .05. bpm: beat per minute, CB: cross the box, FB: front the box.. 54.

(64) 4.2 Joint Range of Motion (ROM) in Different Box Jumps. There were interaction effects between box jumps and rates. in. joint. ROM. of. hip. flexion/extension. and. ankle. internal/external rotation ( Figure 4.2-1). In different box jumps under different rates, the ROM of hip flexion/extension was found significantly greater in CB than in FB among all r at e s (6 0 b pm , 7 5 b pm a nd 9 0 b p m ) ; h o w ev e r, o nl y w h e n it reached. to. 90. bpm. could. be. found. that. ROM. of. ankle. internal/external rotation was significantly lesser in CB than in FB (Figure 4.2-1). While in different rates under different box. jumps,. significant. differences. only. appeared. in. FB. instead of CB; the ROM of hip flexion/extension was found significantly greater in both 60 bpm and 75 bpm than in 90 bpm, while 60 bpm and 75 bpm had no significant difference. For the ROM of ankle internal/external rotation, which in both 60 bpm and 90 bpm were significantly greater than which in 75 bpm,. though. there. was. no. significant. between 60 bpm and 90 bpm (Figure 4.2-1).. 55. difference. found.

(65) Fi gure 4.2-1 . ROM - Int eracti on effect . Note. *p < .05: significant difference between box jumps. ǂ. p < .05: significant difference among rates.. ROM: range of motion, CB: cross the box, FB: front the box , F/E:. Flexion/Extension,. IR/ER:. rotation.. 56. Internal. rotation/External.

(66) For non-interaction effects, significant differences of ROM were found in hip joint and knee joint while comparing different box jumps (Figure 4.2-2). In hip internal/external rotation, ROM in CB was lesser than in FB. And in both knee flexion/extension and adduction/abduction, ROM was found greater in CB than in FB (Figure 4.2-2). For different rates, significant differences of ROM were also found in hip joint and knee joint instead of ankle joint ( Figure 4.2-2). In hip internal/external rotation, ROM in 75 bpm was greater than in 90 bpm. While in knee flexion/extension, adduction/abduction and internal/external rotation, ROM in 90 bpm seemed to be the least among all rates (Figure 4.2-2).. 57.

(67) Fi gure 4 . 2-2 . ROM - No n -i nt eract i on effect . Note. *p < .05. ROM: range of motion. F/E: Flexion/Extension, Add/Abd: Adduction/Abduction, IR/ER: Internal rotation/External rotation, DF/PF: Dorsiflexion/Plantar flexion, Inv/Env: Inversion/Eversion.. 58.

(68) 4.3 Peak Joint Forces in Different Box Jumps. There was no interaction effect between different box jumps and rates for peak joint forces in lower limbs ( Figure 4.3). For peak joint forces of different box jumps, CB hold less anterior shear force in hip joint, posterior shear force in knee joint and posterior shear force in ankl e joint than FB; h o w e v e r,. for. ankle. anterior. shear. force,. the. result. was. opposite (Figure 4.3). As for peak joint forces in different rates, it was found the most in 90 bpm for knee anterior shear force, knee posterior shear force and ankle medial shear force; while for both hip anterior shear force and ankle anterior shear force, it was found the least in 90 bpm among all rates (Figure 4.3).. 59.

(69) Fi gure 4.3. P eak j oi nt fo rces o f lo wer li mb s in di fferent b ox jumps and rates. Note. *p < .05. CB: cross the box, FB: front the box. Ant F: anterior shear force, Post F: posterior shear force, Med F: medial shear force, Lat F: lateral shear force, Com F: compression force.. 60.

(70) 4.4 Peak Joint Moments in Different Box Jumps. There was no interaction effect between different box jumps and rates for peak joint moments in lower limbs ( Figure 4.4). For different box jumps, there was only one significant difference found in ankle dorsiflexor moment and which was greater in FB than in CB (Figure 4.4). As for different rates, in the circumstance of 90 bpm, joint moment appeared to be the greatest for knee extensor moment, ankle plantar flexor moment,. and. ankle. internal. rotation. moment,. while. the. opposite result was found in hip flexor moment ( Figure 4.4).. 61.

(71) Fi gure 4.4 . P eak j oi nt mo m en ts o f l ower l im bs in d i fferen t b ox jumps and rates. Note. *p < .05. CB: cross the box, FB: front the box. Add M: adduction moment, Abd M: abduction moment, Flex M: flexor moment, Ext M: extensor moment, IR M: Internal rotation moment, ER M: external rotation moment. Inv M: inversion moment, Env M: eversion moment, DF M: dorsiflexor moment, PF M: plantar flexor moment. 62.

(72) Chapter 5 Discussion. 5.1 Joint Kinematics & Kinetics during Different Box Jumps. CB and FB were two similar jumps with the same set ting of the boxes. Because of their properties of movement, we assumed that when subjects performed CB, they have to put more effort on horizontal displacement and joint flexion of lower extremities are needed for the purpose of crossing the box compared with FB. As for FB, there seemed to be more vertical component during the jump tha t may address less on joint flexion of lower extremities.. Changing the speed of the task was thought to be a means to adjust the intensit y in pl yometric exercise s (Houglum, 2001). In the empirical training regimen s, athletes are always t o l d t h a t - t h e f a s t e r, t h e b e t t e r. T h e r e f o r e , i n t h e p r e s e n t s t u d y, w e s e t t h e investigate. how. rates as 60 bpm, 75 bpm, 90 bpm to the. low-to-high. rates. affect. the. biomechanical parameters of the jumps. It is not hard to speculate that the higher the rate, the higher the intensity; thus, we assumed that the biomechanical parameters involved in any changes with the rates should be in a linear relationship as well. 63.

(73) The literatures about different box jumps and rates were limited.. Most. studies. such. as. the. evaluations. of. the. intervention effects as well as the intensity of plyometric exercises investigated maximal heights, peak ground reaction forces, joint angles, foot contact times of maximal exertion of the vertical jumps. The difference between the present study and the previous ones was that we didn ’t emphasize on the maximal effort of the performance but we investigated the patterns instead.. As for joint angles, generally speaking, subjects needed to flex hip joint and knee joint more at a certain checkpoint in order to cross over the box safely in CB than in FB. The joint angles of the ankle may indicate that subjects landed with lateral border of midfoot at landing; then they transformed the foot pressure from lateral border to medial border before the checkpoint of peak landing force. This may be able to be compared to the transition of foot pressure during the gait cycle, and yet the dissimilarit y was that subjects landed with m i d f o o t i n t h i s s t u d y, w h i l e t h e l a n d i n g p o r t i o n w a s h e e l i n gait cycle.. Lephart et al. (2005) noted that increased hip flexion at initial contact, and increased peak knee flexion as well as time to peak knee flexion in jump-landing task provided the desired. effect. for. body to. absorb 64. the. joint. forces. more.

(74) e f f e c t i v e l y.. Furthermore,. hamstrings. were. thought. to. be. tensioned more by increasing angles of hip and knee flexion, thus a posterior force would be created additionally to prevent ACL from. overstressed.. We m a y n o t. be able to directly. c o m p a r e o u r r e s u l t t o L e p h a r t ’s c o n c l u s i o n , s i n c e h i s s t u d y was about the comparison of pre- and post- intervention of pl yo m e t ri c ex e r ci s e a n d r e si st a n c e tr a in in g. H o w ev e r, it ga v e us the notion that if subjects performed more hip and knee flexion at the checkpoints he mentioned in his study during a jump-landing task, the risk of ACL injury may be lessened. According to the patterns of kinematics in the present study, less hip and knee flexion were found in FB at the checkpoint of landing, but more knee flexion was also found in FB at the c h e c k p o i n t o f m a x i m u m k n e e f l e x i o n ; h o w e v e r, m o r e h i p a n d knee flexion were found in CB at the checkpoint of landing, but less knee flexion was also found in CB at the checkpoint of maximum knee flexion. This result may indicate that while performing CB, subjects might have better force absorptions at t h e c h e c kp oi nt o f l a nd in g; h o w e v er, w hi l e p e r fo r min g FB, subjects may have a better stabilization for ACL at. the. checkpoint of maximum knee flexion. As for time to maximum knee flexion, there were no statistical differences between different jumps under each rate.. As for joint moments, it was found in both CB and FB that. the. peak. hip. flexor. moment 65. took. place. after. the.

(75) checkpoint of landing and before the checkpoint of peak landing force, while peak hip extensor moment was noted several milliseconds after the checkpoint of peak landing force. It indicated that both jumps required hip flexor and hip extensor. to. activate. reciprocally. from. the. checkpoint. of. landing to the checkpoint of maximum knee flexion in order to absorb the impact forces and then hip extensor carried out through the checkpoint of maximum knee flexion to take -off for the preparation of next jump. Hip abduction moment could be noted in both jumps before the checkpoint of landing; this w a s c o n s i s t e n t w i t h Le p h a r t ’s f i n d i n g ( 2 0 0 5 ) . A c c o r d i n g t o h i s s t u d y, h e s u g g e s t e d t h a t t h e a c t i v a t i o n o f g l u t e u s m e d i u s prior to the initial contact could allow subject s to position their thighs in order to cope with undesired hip adduction and k n e e v a l g u s c a u s e d b y i m p a c t f o r c e a t l a n d i n g ; i n t h i s w a y, knee stability would be increased. Hip adduction moment and hip external rotation moment were found in FB throughout f ro m l a nd in g t o ta k e -o ff ; ho w e v e r, i n C B, i t w as fi r st hi p adduction moment and hip external rotation moment. took. place before the checkpoint of maximum knee flexion, then h i p a b d u c t i o n m o m e n t t o o k o v e r a f t e r . E i t h e r w a y, b o t h h i p adductor and hip abductor were more likely to function as assisters for keeping knee joints to a more neutral frontal plane position (Chimera, 2004). The moment of hip external rotation was more obvious in FB than in CB. Because hip external rotator acts as the stabilizer in hip joint by driving 66.