Do Heat And Exercise Training Elicit Similar Adaptations In Vascular Function During Rest And Exercise?

Abstract

Heat, the major byproduct of exercise, may mediate many of the vascular adaptations that come from exercise, making heat therapy a potential alternative to exercise in situations where exercise is not possible. PURPOSE: Compare the effects of 6 weeks of exercise or heat training on resistance artery function at rest and during exercise. METHODS: Thirty-five (18 female) untrained subjects completed either 6-weeks of high-intensity, single-leg, knee-extension exercise (40 mins, 3x per week, n = 11), localized heat training (pulsed short-wave diathermy for 120 minutes, 3x per week n = 13), or a sham heat training protocol (120 minutes, 3x per week, n = 11). Vascular function was measured before and after the training. Specifically, resistance artery function was assessed at rest with the passive leg movement induced hyperemia (PLM). Leg blood flow and vascular conductance were also measured with Doppler Ultrasound and finometry during submaximal, steady-state knee extension (KE) exercise at 10 W and during a maximal graded KE exercise test. RESULTS: Resistance artery function, assessed by peak blood flow during PLM, increased in the exercise (~10.5% increase, P = 0.009) and heating groups (~8.5% increase, P = 0.044) to the same extent (P = 0.625); but tended to decrease in the sham group (P = 0.087). While blood flow during submaximal KE (10 W) did not change in any group, vascular conductance at 10 W tended to increase in the exercise group (19%, P = 0.056) and the heat group (16%, P = 0.036), but did not change in the sham group (P = 0.915). Likewise, maximum vascular conductance during KE significantly increased by ~25% in the exercise (P = 0.030) and heat (P = 0.012) groups but did not change in the sham group (P = 0.699). Importantly, the magnitude of change in resistance artery function, assessed by PLM, was related to the change in maximal vascular conductance (r = 0.50, P = 0.006). Maximum power achieved during KE only increased in the exercise group (~27%, P = 0.001). CONCLUSIONS: Localized heat therapy improved resistance artery function and exercise vascular conductance to the same extent as exercise training but did not yield significant improvements in exercise performance. Thus, heat therapy may be used to achieve many of the vascular benefits of exercise.