Modeling of H-reflexes in human soleus muscle during dynamic ramp contraction

Healthy subjects were asked to make a voluntary plantar-flexing isometric ramp contraction with a maximum force level of 15 Nm, while getting visual force feedback. During this the authors elicited Hoffmann (H-) reflexes with a 100 ms interval before and during the active movement. These experiments showed an increase in the size of the H-reflex prior to the onset of the contraction and a slow decrease towards the end of the contraction. The results were simulated using the modeling language 'SWIM', using a 200 motoneuron pool linked to an EMG output model. The authors simulated the experimental results using either a presynaptic inhibition or a gain recruitment mechanism. Both mechanisms were able to model the experimental outcome.