The Effects of 8 Weeks of Lower Limb Heat Therapy, Moderate-intensity Cycling Exercise, or Both on Vascular Function in Young, Healthy Males and Females

A between-groups interventional design will be used in a cohort of 80 young, healthy males and females 18-35 years old. Interested individuals will be invited to the lab for a screening and familiarization visit (1 hr), in which participants will be introduced to various lab testing protocols to ensure proper performance and tolerance during experimental data collection sessions. Participants will be randomized into one of four groups for an 8-week intervention period: (1) no training (CON), (2) lower limb heat therapy (HEAT), (3) moderate intensity cycling training (EX), or (4) combined training (HEATEX). CON will involve maintenance of regular physical activity habits. HEAT will involve 45 minutes of lower limb hot water immersion (42 °C) using a custom-made heating apparatus 3x/week. EX will involve of 45 minutes of cycling on an ergometer at 40-59% VO2reserve 3x/week. HEATEX will require participants to perform 3x/week of exercise training and heat therapy consecutively and in that order, such that each session is 90 minutes in duration. In total, all groups except CON will be expected to complete 24 intervention sessions. Vascular function will be characterized by measures of endothelial function, arterial stiffness, arterial structure, central hemodynamics, arterial blood flow and shear, and endothelial cell nitric oxide production. Muscle and metabolic adaptations will be characterized by measures of cardiorespiratory fitness, body composition, muscle strength and thickness, and fasting glucose and insulin. Inflammatory profile will be characterized by concentrations of interleukins, heat shock proteins, and cortisol. Thermal physiological adaptations will be characterized by measures of core and skin temperature and sweat rate. Perceptual responses will be characterized by measures of thermal comfort and sensation, calmness, alertness, mood, affect, and ratings of perceived exertion. Intervention adherence will be tracked throughout the intervention period. For the acute investigation (3-hr visit), outcome measures will be assessed before and immediately following the first and last training session. For the chronic investigation (2-hr visit), outcome measures will be assessed at weeks 0, 2, 4, 6, and 8 of the intervention period.