Author(s): MIYAMOTO, K., YAMAMOTO, K., YAMAZAKI, Y., KATO, R., YANAGIYA, T., Institution: JUNTENDO UNIVERSITY, Country: JAPAN, Abstract-ID: 2140

INTRODUCTION:
Previous studies have clarified the dynamics of the muscle-tendon unit (MTU) during normal walking (NW) and running. During walking, muscle fascicles of the medial gastrocnemius contract almost isometrically, while the tendon undergoes stretch-shortening cycles. In contrast, running is characterized by larger changes in muscle fascicle length, which contribute to higher locomotion speeds and distinct MTU behavior compared with walking.
Race walking is characterized by unique kinematic constraints imposed by the rules, particularly the requirement to maintain knee extension from foot contact to mid-stance. However, the behavior of the MTU during race walking has not been clarified. Therefore, the purpose of this study was to investigate differences in the MTU behavior of the medial gastrocnemius between NW and race walking at matched locomotion speeds.

METHODS:
Seven race walkers (4 males and 3 females) performed NW and RW at 8 km/h for 30 s each on a treadmill. The fascicle length and pennation angle of the medial gastrocnemius were measured using ultrasonography, whereas the lower limb joint angles and ground reaction forces (GRF) were simultaneously recorded using a three-dimensional motion capture system and force plates. Electromyography (EMG) was used to record the muscle activity of the medial gastrocnemius. MTU lengths were estimated using a previously reported equation [4], and series elastic element (SEE) lengths were calculated as the difference between MTU and fascicle lengths.
RESULTS:
RW showed a significantly shorter step length and significantly higher step frequency compared to NW. Changes in MTU and fascicle lengths throughout the stance phase were significantly smaller during RW, whereas no significant difference was observed in SEE lengths change. During the first half of the stance phase, fascicle lengthening and SEE shortening occurred simultaneously during NW, whereas both the fascicles and the SEE maintained nearly constant lengths during RW, likely reflecting the kinematic constraint of maintaining knee extension. Additionally, the timing of MTU and SEE shortening during the latter half of the stance phase differed between NW & RW. Regarding EMG activity patterns, RW exhibited an earlier peak in muscle activity than NW.
CONCLUSION:
These findings demonstrate distinct MTU dynamics between NW and RW, suggesting different muscle contraction modes: eccentric-concentric transition in NW versus predominantly isometric contraction in RW.

References
1. Fukunaga et al., Proc Biol Sci, 2001
2. Ishikawa et al., J Appl Physiol, 2005
3. Ishikawa et al., Gait Posture, 2007
4. Hawkins and Hull., J Biomech, 1990