Translational signaling responses preceding resistance training-mediated myofiber hypertrophy in young and old humans

Abstract

While skeletal muscle protein accretion during resistance training (RT)-mediated myofiber hypertrophy is thought to result from upregulated translation initiation signaling, this concept is based on responses to a single bout of unaccustomed resistance exercise (RE) with no measure of hypertrophy across RT. Further, aging appears to affect acute responses to RE, but whether age differences in responsiveness persist during RT leading to impaired RT adaptation is unclear. We therefore tested whether muscle protein fractional synthesis rate (FSR) and Akt/mammalian target of rapamycin (mTOR) signaling in response to unaccustomed RE differed in old vs. young adults, and whether age differences in acute responsiveness were associated with differences in muscle hypertrophy after 16 wk of RT. Fifteen old and 21 young adult subjects completed the 16-wk study. The phosphorylation states of Akt, S6K1, ribosomal protein S6 (RPS6), eukaryotic initiation factor 4E (eIF4E) binding protein (4EBP1), eIF4E, and eIF4G were all elevated (23-199%) 24 h after a bout of unaccustomed RE. A concomitant 62% increase in FSR was found in a subset (6 old, 8 young). Age x time interaction was found only for RPS6 phosphorylation (+335% in old subjects only), while there was an interaction trend (P = 0.084) for FSR (+96% in young subjects only). After 16 wk of RT, gains in muscle mass, type II myofiber size, and voluntary strength were similar in young and old subjects. In conclusion, at the level of translational signaling, we found no evidence of impaired responsiveness among older adults, and for the first time, we show that changes in translational signaling after unaccustomed RE were associated with substantial muscle protein accretion (hypertrophy) during continued RT.

Reliability and smallest worthwhile difference in 1RM tests according to previous resistance training experience in young women

“…A second potential contributing factor for the small increases in muscle strength during repeated 1RM sessions is the possibility of enhanced muscle protein synthesis that leads to muscle hypertrophy sooner than previous thought [43,44]. Although previous studies have suggested that measureable increases in muscle fiber area may require several weeks [45][46][47], recent investigation using computerized tomography has shown that two RT sessions can result in a 3.5% increase in muscle cross-sectional area [48].…”

Blunted hypertrophic response in old mouse muscle is associated with a lower satellite cell density and is not alleviated by resveratrol

“…Since the activation of the AKT/mTOR pathway during overload was not diminished in muscles from old rodents, it is unlikely that a blunted rate of protein translation is a major cause of the attenuated hypertrophic response in old age (Mayhew et al, 2009). Since mechanical growth factor (MGF) and IL-4 are involved in SC activation (Aline and Sotiropoulos, 2012;Della Gatta et al, 2014), an attenuated loading-induced induction of MGF (Owino et al, 2001) and serum response factor, that controls the expression of IL-4, in old age (Lahoute et al, 2008) may result in impaired activation of SCs.…”

β-Hydroxy-β-Methylbutyrate Did Not Enhance High Intensity Resistance Training-Induced Improvements in Myofiber Dimensions and Myogenic Capacity in Aged Female Rats

“…Given the considerable public health relevance of sarcopenia, countermeasure strategies have been studied extensively, ranging from pharmacological-based approaches to nutrition and exercise. Amongst the exercise countermeasures, resistance training (RT) has demonstrated potency and effectiveness in stimulating muscle growth (Mayhew et al, 2009). Even frail elderly individuals beyond the seventh decade of life have shown increases in muscle protein synthesis and myosin heavy chain content following RT (Fiatarone et al, 1994;Yarasheski et al, 1999).…”