Effects of Acute Energy Deficit and Aerobic Exercise on Muscle Quality

10 healthy, male, participants will complete a a 5-day baseline assessment (days -5 to -1) and two consecutive 5-day periods of controlled exercise to increase oxidative capacity (3 days of aerobic exercise per period, 15 kcal/kg FFM/day energy expenditure cycling) and energy intake (15 days in total, with a testing session on morning 16). This will achieve states of energy balance (EB; energy availability - EA - 45 kcal/kg of fat free mass (FFM)/day), required for weight maintenance (days 1 - 5), followed by energy deficit (ED; EA 10 kcal/kg FFM/day), required for weight loss on days 6 - 10. Over the data-collection period, participants will consume deuterium (D2O) tracer to facilitate dynamic proteomic profiling to assess the impact of the intervention on muscle quality (primary outcome measure). Muscle biopsies will therefore be collected on days -5, 1, 6 \& 11, alongside daily saliva samples, and venous blood collection on days -5, 1, 3, 5, 6, 8, 10 \& 11. These samples will be used to assess further, secondary, outcome measures including alterations in intra-muscular lipid profiles (lipid droplet content, morphology and lipid-droplet associated proteins in different subcellular compartments \[intermyofibrillar vs subsarcolemmal\]), alterations in blood metabolites and hormones and skeletal muscle glycogen concentrations. Changes in body mass, body composition and RMR will also be assessed.