INTRODUCTION
This study was supported by National Science Council (NSC 99－2622－B
－037－001－CC3)
ACKNOWLEDGEMENT
How does the toe step affect biomechanical characteristics of lower limb in pinnacle trainer stepping?
Yu-Lin You 1 , Yu-Chi Hsu 1 , Hsiao-Feng Chieh 1 , Chien-Ju Lin 1 , Li-Chieh Kuo 2 , and Fong-Chin Su1,3
1 Department of Biomedical Engineering, 2 Department of Occupational therapy, 3 Medical Device Innovation Center, National Cheng Kung University, Tainan, Taiwan
CLONCLUSION
This study investigated the differences of the biomechanics of the lower extremity between the TS and FC conditions. The current study identified the better stepping posture for exercise training for the different subject group. According to the results of knee joint moment in frontal plane, which showed a greater varus moment at terminal stepping phase in the TS condition than the FC condition. Thus, for the knee medial compartment osteoarthritis subject group, step with foot full contact on pedal may be recommended in order to decrease the medial compartment loading.
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Exercise with fitness equipment is more popular in the recent years. Some of these fitness equipment acted as a close kinetic chain exercise [1], such as stationary bicycle, elliptical trainer and stair climber. Close kinetic chain exercise was performed as the foot fixed and knee motion is accompanied by motion at the hip and ankle [4]. This kind of exercise produced greater compression force and a greater antero-posterior force on knee compared with the open kinetic chain exercises [5]. A modified type of stair-climbing machine (S770, SportsArt, Taiwan) with the curved pedal trajectory for exercising of the lower extremities in the frontal and sagittal planes was developed recent years. Previous study investigated the basic biomechanical characteristics of the lower extremities during stepping. The results of this study found that subjects had greater knee valgus moment during stepping pinnacle trainer (S770, SportsArt Fitness, Taiwan) with trunk kept in a central position than the trunk medial-lateral shift [6]. This result was expected to reduce knee varus moment and further reduce pain intensity for subjects with knee osteoarthritis (OA) as a rehabilitation tool. The major symptoms of knee OA included pain, joint swell, stiffness and limited joint range of motion. These symptoms influence the function activities, such as walking ability and stair climbing, and reduce their quality of life [7-8]. Knee OA patients usually have deteriorated cardiopulmonary function and muscular strength of the lower extremities due to the reduced activities [9-11].
Clinically, there were many treatment for knee osteoarthritis, including muscular strengthening exercise, aquatic exercise, low impact aerobic exercise or traditional physical therapy, such as ultrasound or transcutaneous electrical nerve stimulation. According to the results of previous study, the low impact aerobic exercise and the muscular strengthening of the lower extremities showed greater improvements on functional activities and pain relief [12]. However, in our previous study, we found participants stepped the pinnacle trainer at their comfortable and faster than comfortable speed appeared toe step movement during stepping at the terminal stepping phase rather than heel toe step together. Stepping the pedal with the toe only may involve more ankle strategy during stepping. The different strategies during stepping may result in different training effects and the biomechanical characteristics. However, in order to design proper exercise prescription for specific subject group, the investigation of biomechanical characteristics on different stepping strategies is needed. Thus, the purpose of this study was to investigate the differences of biomechanical characteristics between toe step and heel toe step together during stepping pinnacle trainer.
METHODS Subjects
This study recruited 6 healthy participants and the inclusion criteria contained that subjects without any history of cardiopulmonary, musculoskeletal, neurological disease or other orthopedic injury. The mean age was 24.75 (1.50) years old, the mean height was 164.75 (11.70) cm, and the mean weight was 59.50 (15.33) kg.
Equipment
The stair climber (S770, SportsArt Fitness) was used (Figure 1). The loading level of this fitness equipment was set a level 1. The 3-D motion capture system (Raptor, Motion Analysis Corporation) was used to collect motion data during stepping the stair climber. A 6-axial force and torque sensor was used to collect foot contact force (Mini 85, ATI). Participants stepped this fitness equipment at their comfortable speed.
Methods and protocols
There were 31 reflective markers attached on the anatomical landmarks of the lower extremity and trunk which based on the modified Helen Hayes marker set, including: top of head, spinous process of 7th cervical vertebra (C7), manubrium of sternum, bilateral acromioclavicular joint (AC), bilateral olecranon process, bilateral midpoint of ulnar and radial styloid process, spinous process of 8th thoracic vertebra (T8), sacrum, bilateral anterior superior iliac spines (ASIS), bilateral greater trochanter (GT), bilateral mid lateral aspect of thigh, bilateral medial epicondyles of knee, bilateral lateral epicondyles of knee, bilateral mid lateral aspect of shank, bilateral medial malleoli of ankle, bilateral lateral malleoli of ankle, bilateral middle base between the 2nd and 3rd metatarsal bone of ankle, and bilateral heel. There were two conditions, foot full contacts on the pedal (FC), and the other one condition was toe stepping (TS) at the terminal stepping phase. Every condition performed 5 trials and 15 seconds per trial.
The cycle period contained the stepping phase which is a period when the pedal was at the highest position to the lowest of the track and the recovery phase which movement of pedal is inverse to the stepping phase. Subjects stood on the pedals of pinnacle trainer and the investigator instruct subject to step the pedal, and subjects practiced until they were familiar with this novel-designed machine.
Figure 1. The stair climber (S772, SportsArt Fitness) Figure 2. Subjects on the pinnacle trainer at the starting position
RESULTS AND DISCUSSION
The ankle joint angle in sagittal plane showed a plantar flexion during TS condition at the terminal stepping phase. However, the FC condition showed a dorsiflexion at the terminal stance phase. The TS condition showed greater knee flexion angle than the FC condition. Both conditions showed a similar tendency in the hip joint angle in sagittal plane. In frontal plane, the TS condition had a greater inversion angle and a greater knee valgus angle. However, both conditions have a similar tendency in the hip joint angle in frontal plane. In joint moment comparison, the TS condition showed a greater plantar flexor and a greater hip extensor moment.
Nevertheless, the knee extensor moment was smaller in the TS condition compared to the FC condition. In the frontal plane, the TS condition showed a greater knee varus moment (Figure 3) and a greater hip adductor moment (Figure 4)
0 20 40 60 80 100
-0.10 -0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30
Recovery phase
Varus Valgus
Joint moment (Nm/BW)
Stride cycle (%)
TT Knee FC
Valgus Stepping phase
0 20 40 60 80 100
-1.00 -0.95 -0.90 -0.85 -0.80 -0.75 -0.70 -0.65 -0.60 -0.55 -0.50
A
Stride cycle (%)
TS Adductor FC
Abductor
Hip
Stepping phase Recovery phase
