Beyond their most commonly recognised roles in locomotion and postural support, skeletal muscles also serve as the central node for whole-body metabolic health, acting as, for example, the largest amino acid (AA) reservoir and glucose disposal site in the body. Alongside AA nutrition, muscle contraction in the form of exercise and/ or physical activity is well established to improve metabolic health and induce both favourable physiological adaptations (e.g., muscle mass gains, mitochondrial biogenesis) and secondary health benefits (e.g., improved insulin sensitivity). Indeed, nutrition x contractile interaction is the fundamental basis of muscle mass maintenance across the life course. In stark contrast, the absence of muscle contraction in the form of “disuse” (e.g. through simple inactivity, casting, immobilization, or bed rest) has the opposite effect causing muscle atrophy, functional declines, and metabolic impairment (e.g., muscle insulin resistance). In older adults, events leading to periods of disuse or reduced physical activity are relatively commonplace (i.e., after falls, surgery, or during illness), with the additional complication of an existent background of sarcopenia progression in these individuals. Despite it being largely accepted that the regulatory processes underpinning muscle mass and functional declines with both advancing age and as a result of disuse are complex and multifactorial, we are still some way from complete understanding; with phenomenon such as atrophy resistant versus atrophy susceptible (aRaS) muscles posing novel questions. This presentation will i) outline the importance and underlying mechanisms of skeletal muscle mass maintenance for older adults, ii) highlight the rapidity of skeletal muscle disuse atrophy in both healthy and clinical cohorts, iii) address the observation of aRaS muscles, and iv) finally, provide early-data from studies looking to develop intervention strategies to mitigate losses of muscle mass and function in older surgical patients.