Sex-based comparisons of myofibrillar protein synthesis after resistance exercise in the fed state

Daniel W.D. West, Nicholas A. Burd, Tyler A. Churchward-Venne, Donny M. Camera, Cameron J. Mitchell, Steven K. Baker, John A. Hawley, Vernon G. Coffey, Stuart M. Phillips


We made sex-based comparisons of rates of myofibrillar protein synthesis (MPS) and anabolic signalling after a single bout of high-intensity resistance exercise. Eight men (20 ± 10 y, BMI = 24.3 ± 2.4) and eight women (22 ± 1.8 y, BMI = 23.0 ± 1.9) underwent primed constant infusions of L-[ring-13C6]phenylalanine on consecutive days with serial muscle biopsies. Biopsies were taken from the vastus lateralis at rest, and 1, 3, 5, 24, 26 and 28 h after exercise. 25 g of whey protein was ingested immediately and 26 h after exercise. We also measured exercise-induced serum testosterone since it is purported to contribute to increases in MPS post-exercise and its absence has been hypothesized to attenuate adaptative responses to resistance exercise in women. The exercise-induced area under the testosterone curve was 45-fold greater in men than women in the early (1 h) recovery period following exercise (P < 0.001). MPS was elevated similarly in men and women (2.3- and 2.7- fold, respectively) 1-5 h post-exercise and after protein ingestion following 24 h recovery. Phosphorylation of mTORSer2448 was elevated to a greater extent in men than women acutely after exercise (P = 0.003), whereas increased phosphorylation of p70S6K1Thr389 was not different between sexes. Androgen receptor content was greater in men (main effect for sex, P = 0.049). Atrogin-1 mRNA abundance was decreased after 5 h recovery in both men and women (P < 0.001) and MuRF-1 expression was elevated in men after protein ingestion following 24 h recovery (P = 0.003). These results demonstrate minor sex-based differences in signalling responses and no difference in the MPS response to resistance exercise in the fed state. Interestingly, our data demonstrate that exercise-induced increases in MPS are dissociated from post-exercise testosteronemia and that stimulation of MPS occurs effectively with low systemic testosterone concentrations in women.

  • muscle protein synthesis
  • resistance exercise
  • sex-based comparisons
  • testosterone