H-reflex assessment as a tool for understanding motor functions in postural control

The Hoffmann reflex (H-reflex) has been extensively used to investigate spinal reflex function in clinical and human movement studies. The H-reflex is induced by applying an electric stimulation on a peripheral nerve branch and recording EMG from a muscle innervated by this nerve. The response of the α-motoneuron pool to the stimulation, as indicated by the peak-to-peak amplitude of the H-reflex, reflects the inhibitory and excitatory modulation of the spinal motoneuron pool during a motor task. Recently, the H-reflex modulation in relation to postural control has been addressed in a number of laboratory-based investigations. There has been evidence that the modulation of H-reflex is task-dependent. Specificity of the H-reflex in adaptation to exercise intervention has also been revealed. This chapter provides a discussion on the H-reflex modulation during a variety of postural tasks and its adaptation to exercise training. The soleus (SOL) H-reflex is the focus because this muscle plays a critical role in maintaining upright standing posture and the studies on SOL H-reflex modulation may help us to understand the neural mechanisms in postural control.