The role of afferent feedback in the control of hamstrings activity duringhuman gait

In vertebrates, possibly also in man, the pattern of activation of muscles during locomotion can be generated by the spinal cord (locomotor CPG, centr al pattern generator). However, sensory feedback is crucial to adapt the fu nctioning of the CPG to the external requirements during gait. It is postul ated that afferent input from skin and muscles can contribute to the EMG ac tivation patterns as observed in various limb muscles during gait. The acti vity of the hamstrings at end swing may be partially due to stretch reflexe s of these muscles. At end stance the hamstring activity may be assisted by reflexes from natural skin activation from the dorsum of the foot. In addi tion, more specific actions are also incorporated. For example, sural nerve stimulation induces an activation of biceps femoris (BF) whereas a suppres sion is usually obtained for semitendinosus (ST), indicating that the induc ed activation is aimed at exorotation of the lower leg. Similarly, the pref erential activation of medial versus lateral gastrocnemius (GM versus CL) i n sural nerve induced reflexes could favor such exorotation. It is conclude d that the present evidence points towards a possible contribution of vario us reflexes to the motor output seen during gait for movements both inside and outside the sagittal plane.