Kawakami Y, Sale DG, MacDougall JD, Moroz JS

Eur J Appl Physiol 1998 Feb;77(3):212-216

Six male subjects made maximal isometric plantar flexions unilaterally (UL) and bilaterally (BL), with the knee joint anglepositioned at 90 degrees and 0 degrees (full extension) and the ankle joint kept at 90 degrees. Plantar flexion torque andelectromyogram (EMG) of the lateral gastrocnemius (LG) and the soleus (Sol) muscles were recorded. There was a deficit intorque in BL compared to UL (P smaller than 0.05), and the deficit was greater when the knee was extended than when bent to 90 degrees(13.9% vs 6.6%). The integrated EMG (iEMG) of UL and BL did not differ when the knee was at 90 degrees. On the otherhand, when the knee was extended iEMG of LG was smaller for BL than for UL, suggesting that the larger bilateral deficit whenthe knee was extended was due to a reduced activity of the LG motor units. In addition, the H-reflex recorded from Sol when thecontralateral leg was performing a maximal unilateral plantarflexion was reduced. This would indicate that the force deficit wasassociated with a reduction of motoneuron excitability.