Role of reflex responses of knee musculature during the swing phase of walking in man.

Muscle activation patterns of the quadriceps and hamstrings were studied in normal human subjects walking at comfortable speed on a treadmill. In addition knee angular velocity patterns and swing and stance phases of the step cycle were recorded. Data were collected from normal paces and from paces in which a momentary unexpected resistance was applied to the leg during swing. The application of the resistance caused an advance in the onset of both quadriceps and hamstrings activity. The latency of the onset of activity following the resistance in the quadriceps was 78.2 +/- 26.4 ms and this was considered to indicate a long latency stretch reflex. There was a close association between the onset of quadriceps and hamstrings activity both in the normal and resistance paces. The changes observed in knee angular velocity upon application of the resistance indicate tight control of angular velocity patterns. The results have important implications regarding neural control of muscle during purposive movement and the regulation of sensitivity of muscle receptors during such movements, especially during the periods when the muscle is normally inactive.