Nicholas Barefoot, Michael Kinderman, Grant Malone, Stefanie Wind, Jonathan Wingo, FACSM, Hayley MacDonald. University of Alabama, Tuscaloosa, AL.

BACKGROUND: The effects of aerobic exercise (AE) on vascular health and function are well established, hence it is considered the cornerstone therapy to prevent and treat cardiovascular diseases. Yet, most adults do not engage in the recommended levels of AE to realize these health benefits. Alternate therapeutic modalities, like passive heating (PH), may provide similar acute cardiovascular benefit, but findings and methodologies are inconsistent. METHODS: We evaluated cardiovascular and thermal responses to AE and PH in 7 low-fit but healthy adults (3 women; M±SD age=23±3 y, peak oxygen uptake [VO2]=22.8±2.6 ml·kg-1·min-1) with normal systolic/diastolic blood pressure (SBP/DBP: 116±16/75±11 mm Hg). Participants completed a familiarization visit and 2 randomly assigned 30-min experimental interventions separated by >48 h: AE (recumbent cycling at 40% VO2 reserve) and PH (recumbent rest wearing a water-perfused, tube-lined suit circulating 49 °C water). SBP, DBP, heart rate (HR), vascular stiffness (pulse wave velocity [PWV]), core (Tc) and skin (Tsk) temperature were measured pre-, immediately post-, and 60 min post-intervention. Statistical analyses included descriptive statistics and two-way repeated measure ANOVA. RESULTS: Changes in SBP, DBP, and PWV were not significantly different from rest by time or intervention. HR was elevated from rest immediately following PH and AE (mean difference [MD]±SD=4.8±3.4 beats/min, p=0.04). Tc increased more from rest immediately post-AE vs. PH (0.4±0.3 °C, p=0.01), and remained higher 60 min post-intervention (0.3±0.3 °C, p=0.01). Tsk increased more from rest immediately post-PH vs. AE (3.6±2.6 °C, p=0.01), and remained higher 60 min post-intervention (2.8±1.6 °C, p=0.02). CONCLUSIONS: Thirty min of AE or PH did not elicit significant changes in BP or vascular stiffness outcomes immediately post-intervention or during 60 min of recovery, nor did responses differ by intervention. Tc and Tsk increased compared to rest, but no consistent pattern emerged for AE or PH. Our findings suggest that the “dose” of AE and PH prescribed was insufficient for inducing favorable cardiovascular changes in our sample of young, healthy adults. To determine whether PH can serve as a suitable alternative for those who prefer not to or cannot participate in AE, it should be further investigated among adults with higher BP who stand to benefit the most. Moreover, future studies should focus on identifying the “optimal dose” of PH for therapeutic benefit.

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