The Hoffmann (H) reflex and motor (M) response were studied in soleus and gastrocnemius during voluntary contraction in eight male volunteers.
Aims: To determine if the strength of spindle input to the muscles is the same. To assess if the M response size changes during contraction.
Results: The size of the maximum M response (M max) changed during contraction in each subject. Hence, all H reflex measurements were normalized to the M max at each level of contraction for each subject. The largest H/M max was bigger in soleus than gastrocnemius at every contraction level. The overall largest H/M max for soleus (97%) and gastrocnemius (55%) were achieved at 40 and 100% maximum voluntary contraction (MVC), respectively.
Conclusion: Soleus receives greater spindle feedback than the gastrocnemius both at rest and during voluntary contraction.