interleukin-15 stimulates fat oxidation, glucose uptake, mitochondrial biogenesis and myogenesis in skeletal muscle and adipose tissue. in humans, basal concentrations of il-15 and its alpha receptor (il-15rα) in blood have been inversely associated with physical inactivity and fat mass, particularly trunk fat mass. moreover, in response to a single session of resistance exercise the il-15/il-15rα complex has been related to myofibrillar protein synthesis (hypertrophy).