Acute leg‐cycling exercise attenuates the h‐reflex recorded in soleus but not flexor carpi radialis

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Abstract
The amplitude of the Hoffman reflex (H‐reflex) in the soleus muscle is attenuated after acute bouts of leg‐cycling exercise. The attenuation has been interpreted as a “tranquilizing” effect of exercise controlled by the central nervous system and generalized beyond a single spinal segmental level. If so, the postexercise depression of the H‐reflex should occur in both the soleus and the flexor carpi radialis (FCR) muscle, which is not actively involved during leg cycling. This experiment examined the effect of moderate‐intensity cycling exercise on the H‐reflex recorded in soleus and FCR among 16 men. The H‐reflex was measured immediately before and 10 min after 30 min of either moderate‐intensity leg cycling (60% V̇O2peak) or quiet rest. The acute bout of cycling exercise reduced the H‐reflex in the soleus but not in the FCR. Thus, the attenuation of the H‐reflex after leg cycling does not generalize beyond the spinal segmental level that modulates the involved locomotory muscles; it is likely the result of segmental processes associated with the repetitive stretching or activation of the soleus muscle. Muscle Nerve 28: 609–613, 2003