Circulating Interleukin-6 is Associated with Skeletal Muscle Strength, Quality, and Functional Adaptation with Exercise Training in Mobility-Limited Older Adults

Background Human aging is characterized by a chronic, low-grade inflammation suspected to contribute to reductions in skeletal muscle size, strength, and function. Inflammatory cytokines, such as interleukin-6 (IL-6), may play a role in the reduced skeletal muscle adaptive response seen in older individuals.Objectives To investigate relationships between circulating IL-6, skeletal muscle health and exercise adaptation in mobility-limited older adults.Design Randomized controlled trial.Setting Exercise laboratory on the Health Sciences campus of an urban university.Participants 99 mobility-limited (Short Physical Performance Battery (SPPB) ≤9) older adults.Intervention 6-month structured physical activity with or without a protein and vitamin D nutritional supplement.Measurements Circulating IL-6, skeletal muscle size, composition (percent normal density muscle tissue), strength, power, and specific force (strength/CSA) as well as physical function (gait speed, stair climb time, SPPB-score) were measured pre- and post-intervention.Results At baseline, Spearman's correlations demonstrated an inverse relationship (P1.36 pg/ml). Moreover, baseline IL-6 was inversely associated (PConclusions These findings implicate age-related increases in circulating IL-6 as an important contributor to declines in skeletal muscle strength, quality, function, and training-mediated adaptation. Given the pervasive nature of inflammation among older adults, novel therapeutic strategies to reduce IL-6 as a means of preserving skeletal muscle health are enticing.