Manipulating the Resistance Training Volume in Middle-Aged and Older Adults: A Systematic Review with Meta-Analysis of the Effects on Muscle Strength and Size, Muscle Quality, and Functional Capacity

Background Effective manipulation of the acute variables of resistance training is critical to optimizing muscle and functional adaptations in middle-aged and older adults. However, the ideal volume prescription (e.g., number of sets performed per exercise) in middle-aged and older adults remains inconclusive in the literature. Objective The effects of single versus multiple sets per exercise on muscle strength and size, muscle quality, and functional capacity in middle-aged and older adults were compared. Moreover, the effects of single versus multiple sets per exercise on muscular and functional gains were also examined, considering the influence of training duration. Methods Randomized controlled trials and non-randomized controlled trials comparing single versus multiple sets per exercise on muscle strength, muscle size, muscle quality, or functional capacity in middle-aged and older adults (aged >= 50 years) in the PubMed/MEDLINE, Web of Science, and Scopus databases (01/09/2021, updated on 15/05/2022) were identified. A random-effects meta-analysis was used. Results Fifteen studies were included (430 participants; 93% women; age 57.9-70.1 years). Multiple sets per exercise produced a greater effect than single sets on lower-limb strength (standardized mean difference [SMD] = 0.29; 95% confidence interval [CI] 0.07-0.51; mean difference [MD] = 1.91 kg; 95% CI 0.50-3.33) and muscle quality (SMD = 0.40; 95% CI 0.05-0.75) gains. There were no differences between single versus multiple sets per exercise for upper-limb strength (SMD = 0.13; 95% CI - 0.14 to 0.40; MD = 0.11 kg; 95% CI - 0.52 to 0.75), muscle size (SMD = 0.15; 95% CI - 0.07 to 0.37), and functional capacity (SMD = 0.01; 95% CI - 0.47 to 0.50) gains. In addition, there were no differences between single versus multiple sets on muscle strength and size gains for training durations <= 12 weeks or > 12 weeks. Conclusions Multiple sets per exercise produced greater lower-limb strength and muscle quality gains than single sets in middle-aged and older adults, although the magnitude of the difference was small. In contrast, single sets per exercise were sufficient to improve upper-limb strength, muscle size, and functional capacity in these populations. Despite these findings, researchers should conduct future high-quality, pre-registered, and blinded randomized controlled trials to strengthen the scientific evidence on this topic.