How does the toe step affect biomechanical characteristics of lower limb in pinnacle trainer stepping?
Yu-Lin You1, Yu-Chi Hsu1, Li-Chieh Kuo2, Hsiao-Feng Chieh1,Chien-Ju Lin1, and Fong-Chin Su1,3
1Department of Biomedical Engineering, 2Department of Occupational therapy, 3Medical Device Innovation Center, National Cheng Kung University, Tainan, Taiwan
Introduction: 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 [2]. This kind of exercise produced greater compression force and a greater antero-posterior force on knee compared with the open kinetic chain exercises [2]. In our previous study, we found participants stepped the pinnacle trainer (S770, SportsArt Fitness, Taiwan) 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. The subjects had greater knee valgus moment during stepping pedal with trunk kept in a central position than the trunk medial-lateral shift [3]. Thus, the training effects of this stair climber on knee medial compartment osteoarthritis needs to be verified. However, in order to design proper exercise prescription for specific subject group, the investigation of biomechanical characteristics on different stepping strategies is needed. Purpose: 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: This study recruited 6 healthy participants who were excluded from musculoskeletal diseases. 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. The stair climber (S770, SportsArt Fitness) was used. 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. 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.
Results: 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 and a greater hip abductor moment, but a similar magnitude of ankle eversion moment.
Conclusions: 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.
