Does specific footwear facilitate energy storage and return at the metatarsophalangeal joint in running?

Longitudinal midsole bending stiffness and elasticity are two critical features in the construction of running shoes. Stiff elastic materials (eg, carbon fiber) can be used to alter the midsole bending behavior. The purpose of this study was to investigate the effects of midsole stiffness and elasticity manipulation on metatarsophalangeal (MTP) joint mechanics during running in 19 male subjects at 3.5 m/s. Midsole bending stiffness and elasticity were modified by means of carbon fiber insoles of varying thickness. Stiffening the shoe structures around the MTP joint caused a shift of the point of force application toward the front edge of the shoe-ground interface. Negative work was significantly reduced for the stiffest shoe condition and at the same time a significant increase of positive work at the MTP joint was found. It seems plausible that the increase in positive work originates from the reutilization of elastic energy that was stored inside the passive elastic structures of the shoe and toe flexing muscle tendon units. Further, an increase in midsole longitudinal bending stiffness seems to alter the working conditions and mechanical power generation capacities of the MTP plantar flexing muscle tendon units by changing ground reaction force leverage and MTP angular velocity.

The gearing function of running shoe longitudinal bending stiffness.

The purpose of the present study was to investigate whether altered longitudinal bending stiffness (LBS) levels of the midsole of a running shoe lead to a systematic change in lower extremity joint lever arms of the ground reaction force (GRF). Joint moments and GRF lever arms in the sagittal plane were determined from 19 male subjects running at 3.5 m/s using inverse dynamics procedures. LBS was manipulated using carbon fiber insoles of 1.9 mm and 3.2 mm thickness. Increasing LBS led to a significant shift of joint lever arms to a more anterior position. Effects were more pronounced at distal joints. Ankle joint moments were not significantly increased in the presence of higher GRF lever arms when averaged over all subjects. Still, two individual strategies (1: increase ankle joint moments while keeping push-off times almost constant, 2: decrease ankle joint moments and increase push-off times) could be identified in response to increased ankle joint lever arms that might reflect individual differences between subjects with respect to strength capacities or anthropometric characteristics. The results of the present study indicate that LBS systematically influences GRF lever arms of lower extremity joints during the push-off phase in running. Further, individual responses to altered LBS levels could be identified that could aid in finding optimum LBS values for a given individual.