The h-reflex as an important indicator in kinesiology

Hoffmann's reflex (the H-reflex) is an electrically-induced reflex that is analogous to the mechanically-induced stretch reflex controlled by the spinal cord. The most common measurements performed concerns the electrical response of the soleus muscle to electrical stimulation in the tibial nerve. The response is induced by a discharge occurring in a motoneuron. The latency time of the H-reflex for the soleus muscle amounts to 30-40 ms. An increase in the strength of the stimulus induces a direct response from the muscle, i.e. the M-wave. The latency time of the M-wave amounts to 4-5 ms. A sport training may affect the parameters of the H-reflex. The Hmax/Mmax ratio is the highest among persons engaged in endurance sports and the lowest among those practising speed and strength sports. A decreased amplitude of the H-reflex characterises the level of the central fatigue, while a decrease in the M-wave amplitude is attributed to the peripheral fatigue. Usually, a decrease in Hmax/Mmax ratio is observed post-exercise. Different times of recovery were reported in the literature. No clear quantitative laws have yet been established that govern the course of the reflex as a result of fatigue. The H-reflex still remains within the scope of the interests of kinesiology as a valuable source of information about the reflex functions in the human motor system.