Background: It is unclear how aging affects adaptive responses to resistance exercise training (RET), especially in women. We hypothesized that (i) increases in muscle mass and function after RET would be blunted in older women, and (ii) reduced 'pro-anabolic' changes in gene expression after a single bout of RE may underlie the blunting.
Methods: Muscle biopsies were obtained from 9 older (76-82y) and 16 younger (19-30y) women at rest and 2.5h after RE (6×20 quadriceps maximal voluntary contractions (MVCs)) for measurement of select anabolic (e.g. IGFs, MyoD) and catabolic (e.g. MAFBx, MuRF-1) transcripts by RT-PCR. Thereafter participants undertook a supervised program of RET (4×15 MVCs 3× wk/12wk). We measured knee extensor muscle volume, fatty infiltration, and mechanical muscle quality before and after RET.
Results: Before RET, older women were ~30% weaker (MVC 208 vs. 297N) and had ~40% less quadriceps muscle (0.97 vs. 1.54L) with greater fatty infiltration (14% vs. 10%). The most notable difference in mRNA expression after RE was for regulated in development and DNA damage response 1 (REDD1) (an endogenous suppressor of mammalian target of rapamycin (mTOR) signaling), which was depressed (-80%), but only in young women. Moreover, adaptive responses to RET were blunted in older women with respect to increases in muscle volume (+2.5% (old) vs. +6.2% (young)) and strength (+16% (old) vs. +27% (young)).
Conclusions: Adaptations to RET are markedly blunted in older women, perhaps in-part due to the inability to downregulate REDD1 and thus upregulate mTOR signaling after RE.
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