Mechanisms of Fatigue and Recovery in Upper versus Lower Limbs in Men

PURPOSE: To compare the mechanisms of fatigue and recovery between upper and lower limbs in the same subjects. METHODS: Twelve healthy young males performed a 2-min sustained maximal voluntary isometric contraction (MVC) of the knee extensors (KE) and on another day a 2-min MVC of the elbow flexors (EF). Neuromuscular function evaluations were performed with both transcranial magnetic and peripheral stimulations before (PRE), at the end of the 2-min MVCs (POSTimm), and 5 more times within 8 min of recovery. RESULTS: Decreases in MVC and cortical voluntary activation were ~12% (P < 0.001) and ~25% greater (P = 0.04) in KE than EF at POSTimm. Conversely, twitch response decreased ~29% more (P = 0.02) in EF than KE. Changes in motor-evoked potential with fatigue were not different between upper and lower limbs (P > 0.05) whereas the increase in silent period duration was ~30% greater in EF than KE (P < 0.05). CONCLUSION: Upper and lower limbs presented different magnitudes of total, central and peripheral fatigue. Total neuromuscular fatigue and central fatigue were greater in KE than EF. Conversely, peripheral fatigue and corticospinal inhibition were greater in EF than KE.