Exercise and Dietary Factors in Skeletal Muscle Anabolism Across Aging: Inferences for the Insulin/IGF-1 Axis—A Narrative Review

Resistance training (RT) influences endocrine pathways that control skeletal muscle (SM) growth. This review summarizes 25 years of evidence (January 2000–December 2025) from PubMed, Medline, and ScienceDirect, focusing on three aspects: (1) exercise types such as RT, speed, power, high-intensity interval training, and aerobic training at various intensities; (2) dietary factors, including caloric restriction, total protein, protein sources, amino acids, and carbohydrates; and (3) aging-related physiological factors that may impair the insulin/IGF-1 axis in SM, such as insulin resistance, fat infiltration, physical inactivity, mitochondrial dysfunction, and inflammation. The data from Grade A evidence in systematic reviews and RCTs are prioritized to develop practical recommendations and future research directions for young, middle-aged, older, and very old individuals. Evidence regarding the effects of anabolic amino acids in women, middle-aged, and very old individuals, as well as locally mediated IGF-1 effects of any type of exercise, is limited.