Heat and Exercise in Aging as Therapy (HEAT)

To achieve the study objectives, researchers will first compare the outcomes of local heat therapy to: 1) HIIT and 2) heat pads set to maintain normal skeletal muscle temperature (control group). Then, researchers will compare the outcomes of the local heat therapy and control groups after a subsequent HIIT intervention. This will enable the researchers to assess the effectiveness of local heat therapy (compared to HIIT and preceding HIIT) to improve skeletal muscle health, physical function, blood sugar control. Study Procedures: All participants will visit the laboratory over three days at the start of the study for baseline assessments and sample collection. Participants in the Control (CON) and Local Heat Therapy (LHT) groups will: Phase 1: * Use heat pads on both thighs at a pre-determined temperature for 90 minutes daily, 6 days a week (5 days at home and 1 day in the laboratory; 12 laboratory visits) for the first 12 weeks. * Maintain a log of each heat pad session. * Visit the laboratory over three days at the end of Phase 1 for follow-up assessments and sample collection. Phase 2: * Visit the laboratory three days per week for 12 weeks (a total of 36 visits) for exercise training. * Visit the laboratory over three days at the end of Phase 2 for final assessments and sample collection. Participants in the HIIT Group will: Phase 1: * Visit the laboratory three days per week for 12 weeks (a total of 36 visits) for exercise training. * Visit the laboratory over three days at the end of Phase 1 for final assessments and sample collection.