Effects of Lower Limb Heat Therapy, Exercise Training, or a Combined Intervention on Vascular Function: A Randomized Controlled Trial

Abstract

Purpose To compare the effects of 8 weeks of no intervention (CON), lower limb heat therapy (HEAT), moderate-intensity exercise training (EX), or combined training and therapy (HEATEX) in young, healthy recreationally active adults. Methods Sixty participants (23 ± 3 years, 30 females) were randomly allocated into either CON (n = 15), HEAT (n = 15), EX (n = 14), or HEATEX (n = 16). The primary outcome was vascular function, assessed through brachial artery flow-mediated dilation tests (BA FMD). Secondary measures included arterial stiffness (pulse wave velocity, PWV); cardiorespiratory fitness (VO2peak); body composition; and quadriceps muscle strength. Results There were no differences in BA FMD between the groups before and after the interventions (all p > 0.05). Both interventions with a heating component were associated with within-group reductions in carotid-femoral PWV, and increases in absolute and relative VO2peak after 8 weeks (HEAT: ∆-0.27 [-0.53, -0.02] m/s, ∆0.18 [0.06, 0.29] L/min, ∆2.18 [0.60, 3.76] ml/kg/min, respectively; HEATEX: ∆-0.33 [-0.58, -0.09], ∆0.21 [0.11, 0.32] L/min, ∆2.59 [1.06, 4.12] ml/kg/min, respectively), but no between-group differences were observed (p = 0.25, p = 0.21, and p = 0.55, respectively). There was also a within-group decrease in body fat percentage with EX (∆-1.37 [-2.45, -0.29] %), but no changes in leg strength in any of the groups (p = 0.79). Conclusions This randomized controlled trial is the first to examine the efficacy of lower limb heating against traditionally prescribed exercise training. In our young cohort, 8 weeks of training and/or therapy was insufficient to improve vascular function. More intense protocols and longer interventions involving lower limb heating may be required to elicit improvements in health outcomes.