The Role of Pretibial Muscles in the Motor Control of Quadriceps at Different Positions of the Knee and Hip Joints in Human

The motor activity in muscles is the result of the interaction between central and peripheral nervous system input in the spinal cord. This interaction, which occures at the site of convergence of the common interneurones, can modify the motor activities to meet the demands of the external requirements. Stimulation of group I and II afferents in common peroneal nerve (CPN) in human elicits poly- synaptic excitation of quadriceps motoneurones. The interneurones in this pathway are the point of convergence for many ascending and descending volleys. In this study, the gain modulation of this reflex at the positions of several knee and hip joints was investigated in 14 volunteers. Single 0.2ms pulses were delivered to CPN at the intensity of 1.5 ´ motor threshold in anterior tibials. The excitatory responses were recorded in ongoing EMG of voluntarily contracted ipsi-lateral rectus femoris at different knee and hip positions. The changes of the reflex at different intensities of contraction in rectus femoris at two knee positions of 180o & 130o, were also investigated. The CPQ reflexes showed a significant attenuation with the knee flexion and hip extension (P £ 0.001, P £ 0.01). A positive significant correlation was found between the reflex magnitude, and the level of contraction at extended knee position, however at the flexed position this correlation was not significant. The results of this study indicated a strong inhibition of CPQ reflex, which is possibly raised from activation of stretch receptors in quadriceps muscles. This inhibitory effect is probably acting at premotoneuronal level.