Acute Effect of Foot Strike Pattern on the Morphological and Mechanical Properties of Medial Gastrocnemius-Tendon Unit Based on Real Time Ultrasound

Objective  To explore the effects of foot strike pattern on the morphological and mechanical properties of medial gastrocnemius-tendon unit (MTU).

Methods  Fifteen healthy recreational runners with habitual rearfoot strike pattern (RFS) were recruited to run at 9 km/h wearing cushioned shoes with RFS and forefoot strike pattern (FFS). An ultrasound system, motion capture system and the instrumented treadmill were utilized to capture the ultrasound image of medial gastrocnemius (MG) in-real, and the ground reaction force (GRF) during running. The foot strike angle, and morphological and mechanical properties of the MG/MTU were calculated.

Results  Compared with RFS, FFS runners exhibited: ① greater second peak GRF; ② lower MG shortening length/rate during stance phase and shortening rate during toe-off phase; ③ lower peak shortening speed and higher MG force; ④ greater MTU shortening speed/rate, lengthening and shortening length, speed and power.

Conclusion  It was confirmed that habitual RFS runners had acute partial optimization effect of MTU. Specifically, the MG could produce more force with less muscle contraction, and the MTU could store and release greater energy at the same running speed, thereby improving the efficiency of MG contraction and propulsion efficiency after an acute switch to FFS.