FIG. 3.

H-reflex frequency-dependent depression is recovered after 30 days of step-training and bike-training in spinal cord injury (SCI) animals. H-reflexes were evoked by the stimulation of the tibial nerve and recorded from the interosseus muscles. Representative averages of H-reflex recordings following a train of stimulation at 0.3 Hz (black), and 10 Hz (gray), in untrained (A), bike-trained (B), and step-trained (C) animals. There was a modest decrease in the average amplitude of the H-reflex at 10 Hz compared to 0.3 Hz in untrained animals, whereas this decrease was considerable in bike-trained and step-trained animals. Overall, the animals in the exercised groups showed a marked reduction of the H-reflex amplitude as the stimulation frequency increased (i.e., increased depression of the reflex), compared to the untrained group (D). There was a significant decrease in H-reflex amplitude in bike-trained and step-trained animals compared to untrained animals at both 5 Hz and 10 Hz (D; *p < 0.05; **p < 0.001).