LAUSR

We sought to determine if the myofibrillar protein synthetic (MyoPS) response to a naïve resistance exercise (RE) bout, or chronic changes in satellite cell number and muscle ribosome content, were associated with hypertrophic outcomes in females or differed in those who classified as higher (HR) or lower (LR) responders to resistance training (RT). Thirty-four untrained college-aged females (23.4±3.4 kg/m2) completed a 10-week RT protocol (twice weekly). Body composition and leg imaging assessments, a right leg vastus lateralis biopsy, and strength testing occurred before and following the intervention. A composite score, which included changes in whole-body lean tissue mass (LSTM), vastus lateralis (VL) muscle cross-sectional area (mCSA), mid-thigh mCSA, and deadlift strength, was used to delineate upper and lower HR (n=8) and LR (n=8) quartiles. In all participants, training significantly (p<0.05) increased LSTM, VL mCSA, mid-thigh mCSA, deadlift strength, mean muscle fiber cross-sectional area, satellite cell abundance, and myonuclear number. Increases in LSTM (p<0.001), VL mCSA (p<0.001), mid-thigh mCSA (p<0.001), and deadlift strength (p=0.001) were greater in HR versus LR. The first-bout 24-hour MyoPS response was similar between HR and LR (p=0.367). While a no significant responder*time interaction existed for muscle total RNA concentrations (i.e., ribosome content) (p=0.888), satellite cell abundance increased in HR (p=0.026) but not LR (p=0.628). Pre-training LSTM (p=0.010) VL mCSA (p=0.028), and mid-thigh mCSA (p<0.001) were also greater in HR versus LR. Female participants with an enhanced satellite cell response to RT, and more muscle mass prior to RT, exhibited favorable resistance training adaptations.