Resistance exercise-induced increases in putative anabolic hormones do not enhance muscle protein synthesis or intracellular signalling in young men

Abstract

We aimed to determine whether exercise-induced elevations in systemic concentration of testosterone, growth hormone (GH) and insulin-like growth factor-1 (IGF-1) enhanced post-exercise myofibrillar protein synthesis (MPS) and phosphorylation of signalling proteins important in regulating mRNA translation. Eight young men (20 +/- 1.1 years, BMI = 26 +/- 3.5 kg m(-2)) completed two exercise protocols designed to maintain basal hormone concentrations (low hormone, LH) or elicit increases in endogenous hormones (high hormone, HH). In the LH protocol, participants performed a bout of unilateral resistance exercise with the elbow flexors. The HH protocol consisted of the same elbow flexor exercise with the contralateral arm followed immediately by high-volume leg resistance exercise. Participants consumed 25 g of protein after arm exercise to maximize MPS. Muscle biopsies and blood samples were taken as appropriate. There were no changes in serum testosterone, GH or IGF-1 after the LH protocol, whereas there were marked elevations after HH (testosterone, P < 0.001; GH, P < 0.001; IGF-1, P < 0.05). Exercise stimulated a rise in MPS in the biceps brachii (rest = 0.040 +/- 0.007, LH = 0.071 +/- 0.008, HH = 0.064 +/- 0.014% h(-1); P < 0.05) with no effect of elevated hormones (P = 0.72). Phosphorylation of the 70 kDa S6 protein kinase (p70S6K) also increased post-exercise (P < 0.05) with no differences between conditions. We conclude that the transient increases in endogenous purportedly anabolic hormones do not enhance fed-state anabolic signalling or MPS following resistance exercise. Local mechanisms are likely to be of predominant importance for the post-exercise increase in MPS.

Figure 1. Whole blood lactate (A) and serum GH (B), IGF-1 (C) testosterone (D) and cortisol (E) concentrations at rest and after LH and HH exercise protocols

Inset: net area under the curve (rest = 0); filled bars – HH, open bars – LH. HH significantly greater than LH for corresponding time points and for AUC, *P < 0.05, †P < 0.01, ‡P < 0.001. Values are means ±s.e.m.

Figure 2. Rate of myofibrillar protein synthesis in the fed state at rest and following LH and HH exercise protocols

*Significantly different from rest, P < 0.05. Values are means ±s.e.m.

Figure 3. Phosphorylated to total protein ratio of JAK2 (A), STAT3 (B), p70S6K (C) and eEF2 (D) at rest and after LH and HH exercise protocols

*Significantly different from rest, P < 0.05. Values are means ±s.e.m.