Passive torque influences the Hoffmann reflex pathway during the loading and unloading phases of plantar flexor muscles stretching

This study investigated the influence of passive tension on Hoffmann reflex during the loading (muscle stretched by passive joint movement) and unloading phase (joint returned to initial position) of muscle stretching. The maximal H ‐reflex amplitude (Hmax) was recorded in soleus in 19 young adults during the loading and unloading phases of a passive 30 ° dorsiflexion, from 90° ankle angle (reference position).Hmax was evoked at similar angles (Protocol‐1) or similar passive torque (PT;Protocol‐2) during the loading and unloading phases, or during two loading phases separated by a 5‐min stretch hold at 30° ankle dorsiflexion relative to the reference position (Protocol‐3). Homosynaptic depression (HD) was assessed with paired H reflexes (0.5‐s interstimulus interval) during the loading and unloading phases (Protocol‐4;n=13). InProtocol‐1, PT was lesser andHmax greater during the unloading than the loading phase (p <  0.001). InProtocol‐2, no difference inHmax was observed between phases. InProtocol‐3, PT was lesser andHmax greater during the second than the first loading phase (p <  0.001). Changes in PT during in these three protocols were associated with those inHmax (r2 ≥ 0.97). InProtocol‐4, HD increased and decreased during the loading and unloading phases, respectively (p <  0.001), without differing between phases. Additional experiments (n=12) showed a similar modulation ofHmax in gastrocnemius medialis during loading and un...
Source: Physiological Reports - Category: Physiology Authors: Tags: ORIGINAL ARTICLE Source Type: research