Adaptation of postural response to voluntary arm raises during locomotion in humans

Adaptation of the response to voluntary rapid arm flexion during 3 phases of the step cycle in humans are examined. The onset of arm movement was similar to the standing condition and was unaffected by the phase of the step cycle. The locomotor cycle in contrast was altered. These changes improved the stability of the subjects by shortening the appropriate stance or swing phase of the step cycle. Only the onset of the ipsilateral biceps femoris response which represents the postural adaptation was dependent on the phase of the step cycle. When the subjects were asked to flex their arm in early swing, the biceps femoris was enhanced after the onset of the arm movement. This suggests that the postural responses during locomotion may not necessarily be anticipatory in nature, but more functional.