Differential effects of resistance and endurance exercise in the fed state on signalling molecule phosphorylation and protein synthesis in human muscle

Abstract

Resistance (RE) and endurance (EE) exercise stimulate mixed skeletal muscle protein synthesis. The phenotypes induced by RE (myofibrillar protein accretion) and EE (mitochondrial expansion) training must result from differential stimulation of myofibrillar and mitochondrial protein synthesis. We measured the synthetic rates of myofibrillar and mitochondrial proteins and the activation of signalling proteins (Akt-mTOR-p70S6K) at rest and after an acute bout of RE or EE in the untrained state and after 10 weeks of RE or EE training in young healthy men. While untrained, RE stimulated both myofibrillar and mitochondrial protein synthesis, 67% and 69% (P < 0.02), respectively. After training, only myofibrillar protein synthesis increased with RE (36%, P = 0.05). EE stimulated mitochondrial protein synthesis in both the untrained, 154%, and trained, 105% (both P < 0.05), but not myofibrillar protein synthesis. Acute RE and EE increased the phosphorylation of proteins in the Akt-mTOR-p70S6K pathway with comparatively minor differences between two exercise stimuli. Phosphorylation of Akt-mTOR-p70S6K proteins was increased after 10 weeks of RE training but not by EE training. Chronic RE or EE training modifies the protein synthetic response of functional protein fractions, with a shift toward exercise phenotype-specific responses, without an obvious explanatory change in the phosphorylation of regulatory signalling pathway proteins.

mTOR signaling response to resistance exercise is altered by chronic resistance training and detraining in skeletal muscle

“…In the present study, we showed attenuated phosphorylation of p70S6K and rpS6 with chronic resistance exercise-like electrical stimulation inducing a maximal isometric contraction. Although few studies examined change in phosphorylation status with training in animal study, a previous study in humans examined the anabolic signaling response to a bout of resistance exercise before and after 10 wk of resistance training (41). This study demonstrated that the duration of elevated Akt, p70S6K, and GSK3-␤ phosphorylation was reduced in trained participants compared with untrained participants, and rpS6 phosphorylation, which was elevated in the untrained state, was not increased after the 10-wk training period (41).…”

“…Although few studies examined change in phosphorylation status with training in animal study, a previous study in humans examined the anabolic signaling response to a bout of resistance exercise before and after 10 wk of resistance training (41). This study demonstrated that the duration of elevated Akt, p70S6K, and GSK3-␤ phosphorylation was reduced in trained participants compared with untrained participants, and rpS6 phosphorylation, which was elevated in the untrained state, was not increased after the 10-wk training period (41). Furthermore, another human study reported that the phosphorylation of p70S6K and rpS6 did not increase after a session of resistance exercise in highly resistance-trained subjects (power lifters), whereas increases in these phosphoproteins were observed in untrained subjects (8).…”

Physiological stimuli necessary for muscle hypertrophy

“…The activation of mTOR signaling pathways, however, appears to be small or brief after cycle exercise compared to resistance exercise. For example, S6K1 phosphorylation has been shown to increase above basal levels immediately after both cycle and resistance exercise 46) ; but, after 4 h, the elevation of S6K1 phosphorylation remained only after the resistance exercise 46) . Furthermore, one study showed that myofibrillar protein synthesis was stimulated over the 4 h period following resistance exercise, but not after cycle exercise 46) .…”

“…For example, S6K1 phosphorylation has been shown to increase above basal levels immediately after both cycle and resistance exercise 46) ; but, after 4 h, the elevation of S6K1 phosphorylation remained only after the resistance exercise 46) . Furthermore, one study showed that myofibrillar protein synthesis was stimulated over the 4 h period following resistance exercise, but not after cycle exercise 46) . These demerits of cycling exercise, resulting from relatively small mechanical stresses, may account for the small effect size and many training sessions required for muscle hypertrophy compared to resistance training.…”

Efficacy and consequences of very-high-protein diets for athletes and exercisers

“…Resistance exercise increases the synthesis of muscle myofibrillar proteins (14) . Sufficient amino acids must be consumed to support increased synthesis.…”