Soleus and vastus medialis H-reflexes: Similarities and differences while standing or lying during varied knee flexion angles

The H-reflex may be a useful measure to examine the lower extremity muscles activation and inhibition following an injury. Recording the vastus medialis H-reflex amplitudes in healthy subjects while standing or lying during varied knee flexion angles may establish a reference for comparison for patients with ACL injury. Vastus medialis and soleus H-reflexes were recorded from 14 healthy subjects while lying and standing during 0, 30, 45, and 60° knee flexion. EMG unit was used to electrically stimulate the tibial and femoral nerves (using 0.5 ms pulses at 0.2 pps of H-maximum amplitude) and to record four traces of the soleus and vastus medialis H-wave and one trace of the M-wave peak-to-peak amplitudes. Repeated measures three-way ANOVAs were calculated with the global α = 0.05. Results showed that (1) the average soleus H-reflex amplitude was significantly less during standing than lying across all knee flexion conditions, (2) the average vastus medialis H-reflex amplitudes showed no measurable significant differences between neutral standing compared with lying, (3) the average vastus medialis H-reflex amplitudes were significantly greater during standing knee flexion conditions (30, 45, and 60°) than lying or neutral standing, and (4) there were no differences between soleus and vastus medialis H-reflex amplitudes during lying across all knee flexion conditions. Data from H/M ratio follow the same pattern of H-amplitude. Recording the vastus medialis H-reflex amplitude during standing and knee flexion may be a reflective of the knee function. It is more specific than the soleus H-reflex because it reflects the changes in the excitability of the quadriceps motoneurons acting directly around the knee joint.