Credibility and strength of evidence for exercise, nutritional, and combined interventions on muscle function and physical performance in older adults: an umbrella review of meta-analyses of randomized controlled trials

Age-related declines in muscle mass, strength, and physical performance contribute to frailty, falls, and disability in older adults. This umbrella review evaluated the strength of evidence for exercise, nutritional, and combined interventions on muscle-related and functional outcomes in older adults. PubMed, Embase, Web of Science, and Cochrane Library were searched to March 2026 for systematic reviews with meta-analysis of randomized controlled trials. The review protocol was registered in PROSPERO (CRD420261371480). Reviews were appraised using AMSTAR 2, and associations were interpreted according to pooled effects, heterogeneity, review quality, and credibility indicators where available. Because several source reviews did not report all conventional umbrella-review credibility components, evidence credibility was appraised using an adapted, transparent framework rather than treating missing diagnostics as absence of bias. Twenty-eight reviews were retained; eighteen contributed plottable pooled estimates. Methodological confidence was mixed: 10 reviews were rated high or moderate by AMSTAR 2 and 18 were rated low or critically low. Nutrition-only evidence was most favorable for muscle-mass outcomes in sarcopenic or vulnerable phenotypes, but effects on gait speed, SPPB, or frailty were inconsistent without exercise. Combined exercise plus nutrition interventions showed favorable estimates for selected strength and functional outcomes, although several large SMDs came from small or selected sarcopenic samples and require cautious clinical interpretation. The most consistently supported downstream clinical evidence was for exercise-based fall prevention, with reductions in fall rate, risk of falling, and fall-related fractures. The available evidence most consistently supports exercise-containing interventions, particularly for fall-related outcomes. Nutrition-only interventions may provide modest benefits for muscle-mass outcomes in selected vulnerable populations, while combined interventions may improve some strength and functional outcomes. These interpretations remain limited by review overlap, clinical heterogeneity, variable methodological quality, and incomplete credibility assessments. PROSPERO CRD420261371480.