Human skeletal muscle-specific hypertrophy with exercise training and aging: a comprehensive review

Age-related skeletal muscle atrophy is a muscle group-specific process. Therefore, we were interested in understanding exercise-induced hypertrophy across different muscles in older individuals. This review provides a comprehensive summary of the available information on muscle-specific hypertrophy responses to exercise training with aging (≥60 yr). In total, 6,018 peer-reviewed publications were reviewed for inclusion [e.g., supervised resistance (RE) or aerobic (AE) exercise training; MRI, CT, or ultrasound-determined muscle size], resulting in 1,417 individuals from 68 studies (RE: n = 1,254; AE: n = 163). Data were divided across age (60-69, 70-79, 80-89, and ≥90 yr) and duration (≤9, 10-14, 15-19, 20-24, and ≥25 wk), with the majority coming from the sexa- and septuagenarians (n = 1,335, 94%) and 10-14 wk of training (n = 806, 57%). The number of muscle groups (RE: 7, AE: 8) and subcomponent muscles (RE: 10, AE: 16) was a low representation of the whole body musculature, with 79% of the data (n = 1,113) coming from the quadriceps. The 10-14 wk responses showed a range of unique muscle-specific hypertrophy and atrophy (RE: 60-69 yr: 2%-14% across 6 muscles; 70-79 yr: 1%-12% across 9 muscles; AE: 70-79 yr: -6% to +9% across 22 muscles). The large quadriceps-only resistance exercise training dataset (60-79 yr) showed that no additional hypertrophy was observed with increased training repetitions (i.e., dose) and that men and women elicited an equivalent hypertrophic training response. The optimal exercise training mode(s) and dose(s) for all of the skeletal muscles of sexa-, septa-, octo-, and nonagenarian women and men are far from being elucidated based on the current scientific literature.