Recurrent inhibition is higher in eccentric compared to isometric and concentric maximal voluntary contractions

This study was designed to investigate the influence of muscle contraction type on spinal recurrent inhibition during maximal voluntary contractions (MVC) of the plantar flexor muscles.

To that purpose, the paired Hoffmann-reflex (H-reflex) technique permitted to assess changes in recurrent pathway by comparing the modulations of test, reference and conditioning H-reflexes (H', H_ref and H₁ respectively) in the soleus muscle during isometric, concentric and eccentric MVC. Twenty-five subjects participated in an experimental session designed to assess the activity of the recurrent inhibition pathway.

The results indicate that both the electromyographic activity and the amplitude of H₁ normalized to the maximal M-wave (M_max ) were similar regardless of the muscle contraction type while the ratio between H' and H₁ amplitudes was significantly smaller during eccentric compared with isometric and concentric MVC. Furthermore, H_ref and H' amplitudes did not differ significantly during both isometric and concentric MVCs while H' amplitude was significantly lower than H_ref amplitude during eccentric MVC. In addition, the V/M_max ratio was similar for all muscle contraction type and greater H' amplitude was significantly correlated with greater V-wave amplitude regardless of the muscle contraction type.

Together, the current results indicate that recurrent inhibition is elevated for the soleus muscle during eccentric compared to isometric and concentric MVC. Data further suggest that the Renshaw cell activity is specifically controlled by the descending neural drive and/or peripheral neural mechanisms during eccentric MVC.