Exercise effects on muscle quality in older adults: a systematic review and meta-analysis

To systematically review and analyse the effects of exercise on morphological and neuromuscular muscle quality (MQ) outcomes in older adults and assess a range of possible moderators that may affect the impact of exercise on MQ outcomes. Using PRISMA guidelines, randomised controlled trials were searched in CINAHL, EMBASE, LILACS, PubMed, SciELO, Web of Science, MedNar, OpenGrey and OpenThesis databases. Eligible trials examined the effects of exercise interventions on morphological and neuromuscular MQ in older adults (>= 60 years). Twenty-one trials (n = 973 participants) were included. Exercise significantly improved morphological MQ (effect size (ES) = 0.32, 95% CI 0.13-0.51, P < 0.001) with significant results maintained for studies assessing muscle density and intermuscular adipose tissue (ES = 0.45-0.52, P < 0.05). For neuromuscular MQ, exercise provided significant positive effects (ES = 0.49, 95% CI 0.29-0.69, P < 0.001) but only maintained for physically healthy participants (ES = 0.43, P < 0.001), resistance exercise interventions (ES = 0.64, P < 0.001), or studies assessing 1-RM or knee extensor isokinetic muscle strength relative to leg lean mass (ES = 0.48-0.62, P = 0.001). Associations between exercise duration and changes in MQ measures were not observed (P > 0.05). Supervised exercise interventions significantly improved different measures of MQ regardless of exercise duration, although these effects were small-to-moderate and not supported across all population-, exercise-, and methods-related features.