Intramuscular Anabolic Signaling and Endocrine Response Following Resistance Exercise: Implications for Muscle Hypertrophy

Abstract

Maintaining skeletal muscle mass and function is critical for disease prevention, mobility and quality of life, and whole-body metabolism. Resistance exercise is known to be a major regulator for promoting muscle protein synthesis and muscle mass accretion. Manipulation of exercise intensity, volume, and rest elicit specific muscular adaptations that can maximize the magnitude of muscle growth. The stimulus of muscle contraction that occurs during differing intensities of resistance exercise results in varying biochemical responses regulating the rate of protein synthesis, known as mechanotransduction. At the cellular level, skeletal muscle adaptation appears to be the result of the cumulative effects of transient changes in gene expression following acute bouts of exercise. Thus, maximizing the resistance exercise-induced anabolic response produces the greatest potential for hypertrophic adaptation with training. The mechanisms involved in converting mechanical signals into the molecular events that control muscle growth are not completely understood; however, skeletal muscle protein synthesis appears to be regulated by the multi-protein phosphorylation cascade, mTORC1 (mammalian/mechanistic target of rapamycin complex 1). The purpose of this review is to examine the physiological response to resistance exercise, with particular emphasis on the endocrine response and intramuscular anabolic signaling through mTORC1. It appears that resistance exercise protocols that maximize muscle fiber recruitment, time-under-tension, and metabolic stress will contribute to maximizing intramuscular anabolic signaling; however, the resistance exercise parameters for maximizing the anabolic response remain unclear.

β-hydroxy-β-methylbutyrate free acid supplementation may improve recovery and muscle adaptations after resistance training: a systematic review

“…In agreement with Wilson et al [13], HMB-FA did not affect the testosterone response to resistance exercise. Although these findings provide support for the potential anabolic benefits associated with HMB-FA supplementation, transient elevations in the hormonal milieu after resistance exercise may not be related to exercise-induced muscle hypertrophy; thus, whether the observed increases in anabolic hormones would translate into greater muscle hypertrophy remains questionable [21,22].…”

FSTL1 as a Potential Mediator of Exercise-Induced Cardioprotection in Post-Myocardial Infarction Rats

“…Since exercise has muscle ischemia-like effects through hypoxia48, it may exert cardiac protective action through a similar mechanism to ischemia. Exercise is a strong stimulator of muscle growth, metabolism and endocrine function49. Thus, both the increased muscle mass and ischemia-mimic effect through exercise may contribute to the increased circulating levels of FSTL1.…”

Night time resistance exercise alters muscular IL-6-related protein signaling, but not muscle growth after 10 weeks of resistance training in male rats

“…Resistance training (RT) has been recognized as an effective approach to improve muscle mass (Gonzalez et al 2016). Little is known regarding the optimal time-of-day (TOD) to conduct resistance training.…”