Temporal depression of the soleus H-reflex during passive stretch

Abstract

Synaptic efficacy associated with muscle spindle feedback is regulated via depression at the Ia-motoneurone synapse. The inhibitory effects of repetitive Ia afferent discharge on target motoneurones of different sizes were investigated during a passive stretch of ankle extensors in humans. H-reflex recruitment curves were collected from the soleus muscle for two conditions in ten subjects. H-reflexes were elicited during passive stretch at latencies of 50, 100, 300, and 500 ms after a slow (20°/s) dorsiflexion about the right ankle (from 100 to 90°). Control H-reflexes were recorded at corresponding static (without movement) ankle angles of 99, 98, 94, and 90° of flexion. The slope of the H-reflex recruitment curves (Hslp) was then calculated for both conditions. H-reflex values were similar for the static and passive stretch conditions prior to 50-100 ms, not showing the early facilitation typical of increased muscle spindle discharge rates. However, the H-reflex was significantly depressed by 300 ms and persisted through 500 ms. Furthermore, less than 300 ms into the stretch, there was significantly greater H-reflex depression with a lower stimulus intensity (20 % Mmax) versus a higher stimulus intensity (Hmax), though the effects begin to converge at later latencies (>300 ms). This suggests there is a distinct two-stage temporal process in the depression observed in the Ia afferent pathway for all motoneurones during a passive stretch. Additionally, there is not a single mechanism responsible for the depression, but rather both heterosynaptic presynaptic inhibition and homosynaptic post-activation depression are independently influencing the Ia-motoneurone pathway temporally during movement.

The neuromechanical adaptations to Achilles tendinosis

“…However, this is different from the consequence of passive muscle stretching. When stretching, the muscle spindle is stretched, which enhances the presynaptic inhibition and, consequently, the suppressed H-reflex response (Robertson et al 2012). J Physiol 593.15 An elevated V-wave was also seen on the tendinotic limb in individuals with Achilles tendinosis in the present study, which indicates an up-regulated descending neural drive.…”

“…When stretching, the muscle spindle is stretched, which enhances the presynaptic inhibition and, consequently, the suppressed H‐reflex response (Robertson et al . ).…”

Independent segmental inhibitory modulation of synaptic efficacy of the soleus H-reflex

“…Soleus H-reflexes were administered according to procedures outlined by Hugon (1973) and described previously (Robertson et al 2012). H-reflexes and motor responses (M-wave) were measured via two active bipolar surface electromyogram (EMG) recording electrodes (Ag/AgCl) of 1.0 cm diameter with an interelectrode distance of 2.0 cm and placed over the soleus and tibialis anterior muscles of the right lower leg.…”

Applications of the H-reflex in kinesiology: a systematic review

“…Some researchers [50,60] report an influence of muscle stretching on H-reflex depression. It can be caused by heterosynaptic presynaptic inhibition and homosynaptic post-activation depression [60].…”

“…Some researchers [50,60] report an influence of muscle stretching on H-reflex depression. It can be caused by heterosynaptic presynaptic inhibition and homosynaptic post-activation depression [60]. In particular, these two phenomena could be the reason for reduced H-reflex volatility and a general reduction in the slope, or gain of the H-reflex.…”