Effects of long term bed rest on stretch reflex responses of elbow flexor muscles

Stretch reflex responses of m. biceps brachii and m. brachioradialis of ten normal adults were studied before and after 20 days of strict bed rest. A standard torque perturbation (15 Nm, 170 ms) was applied to the forearm to induce reflex electromyographic (EMG) activities of the two muscles investigated. Totally 30 perturbations were applied during submaximal isometric elbow flexion movements at 80 deg flexed joint angle, and ensemble averaged EMG waveforms were calculated by aligning the signal to the onset of perturbations. All subjects showed that both short and long latency stretch reflex FMG activities of m. biceps brachii were reduced immediately after 20 days bed rest, and then recovered gradually to pre-bed rest levels at one- to two-months after bed rest, whereas there was no such variation in the stretch reflex induced in m. brachioradialis. It was demonstrated that the muscle stretch reflex gain might be reduced with long-term inactivity, but the effects on stretch reflex gains were different in the two tested muscles.