ACUTE FATIGUE PARADOXICALLY INCREASES VELOCITY AND POWER IN A SEX AND MYOSIN ISOFORM DEPENDENT MANNER

A.W. Ricci, G.E. Privett, K.W. Needham, D.M. Callahan University of Oregon Muscle fatigue is the acute reduction in contractile function following repeated or prolonged muscle activation, primarily driven by the accumulation of intracellular metabolites. However fatigue persists after recovery of metabolic homeostasis. Because muscle contractile function depends on the interrelated function of multiple intracellular proteins, fatigue-induced post-translational modification of these proteins might explain the temporal dissociation of fatigue from metabolic homeostasis. PURPOSE: Our study explored the potential for protein modification to acutely influence contractile function by measuring the effects of in vivo fatigue on single fiber contractile performance in vitro. METHODS: Seven elite athletes (3 male, 4 female) performed a single bout of unilateral fatiguing knee extensions to task failure. Immediately after, bilateral percutaneous needle muscle biopsy was performed on the vastus lateralis muscle to provide a fatigued and control sample. Tissue divided at time of biopsy for phosphoproteomic analysis (western blot) and single fiber contractile mechanics. Myosin heavy chain (MHC) isoform was determined for fiber following mechanical assessment (SDS-PAGE). RESULTS: We found that fatigue did not affect isometric tension (143.35±31.57 mN/mm2; 146.0±28.6 mN/mm2; p=0.55). However, maximum shortening velocity was increased with fatigue (0.95±0.49 ML/s; 1.28±0.65 ML/s; p Study supported by the Wu Tsai Human Performance Alliance