Inclusion Criteria:  Men between the ages of 35 and 59 years Free of any physical limitations as determined by the Exercise Preparticipation Health Screening Questionnaire for Exercise Professionals (PHSQEP), and a Physical Activity Readiness Questionnaire for Everyone (PAR-Q+) Regularly engaged in endurance exercise (running, cycling, swimming) for a minimum of three years, a weekly training volume of 5-10 hours, and a maximal oxygen uptake of 45.00 ml·kg-1·min-1 or higher as determined by completion of VO2peak assessment (Visit #1).  Exclusion Criteria:  Recent musculoskeletal injuries or surgeries Any chronic illness that requires continuous medical care Current incarceration, cognitive impairment or inability to provide consent Present or past use of performance-enhancing drugs