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. 2016 Mar 16;3(2):286-297.
doi: 10.1080/23328940.2016.1156215. eCollection Apr-Jun 2016.

Substantive Hemodynamic and Thermal Strain Upon Completing Lower-Limb Hot-Water Immersion; Comparisons With Treadmill Running

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Free PMC article

Substantive Hemodynamic and Thermal Strain Upon Completing Lower-Limb Hot-Water Immersion; Comparisons With Treadmill Running

Kate N Thomas et al. Temperature (Austin). .
Free PMC article

Abstract

Exercise induces arterial flow patterns that promote functional and structural adaptations, improving functional capacity and reducing cardiovascular risk. While heat is produced by exercise, local and whole-body passive heating have recently been shown to generate favorable flow profiles and associated vascular adaptations in the upper limb. Flow responses to acute heating in the lower limbs have not yet been assessed, or directly compared to exercise, and other cardiovascular effects of lower-limb heating have not been fully characterized. Lower-limb heating by hot-water immersion (30 min at 42°C, to the waist) was compared to matched-duration treadmill running (65-75% age-predicted heart rate maximum) in 10 healthy, young adult volunteers. Superficial femoral artery shear rate assessed immediately upon completion was increased to a greater extent following immersion (mean ± SD: immersion +252 ± 137% vs. exercise +155 ± 69%, interaction: p = 0.032), while superficial femoral artery flow-mediated dilation was unchanged in either intervention. Immersion increased heart rate to a lower peak than during exercise (immersion +38 ± 3 beats·min-1 vs. exercise +87 ± 3 beats·min-1, interaction: p < 0.001), whereas only immersion reduced mean arterial pressure after exposure (-8 ± 3 mmHg, p = 0.012). Core temperature increased twice as much during immersion as exercise (+1.3 ± 0.4°C vs. +0.6 ± 0.4°C, p < 0.001). These data indicate that acute lower-limb hot-water immersion has potential to induce favorable shear stress patterns and cardiovascular responses within vessels prone to atherosclerosis. Whether repetition of lower-limb heating has long-term beneficial effects in such vasculature remains unexplored.

Keywords: acute exercise; immersion; lower-limb heating; passive heat; shear stress.

Figures

Figure 1.
Figure 1.
Change in core temperature from baseline throughout exercise and water immersion measured at 30-s intervals. Data points represent the group mean and error bars are SD.
Figure 2.
Figure 2.
Superficial femoral artery total (black bars), antegrade (checked bars) and retrograde (gray bars) shear rate at baseline and post-intervention. Bars represent group mean, error bars are SE. * interaction: intervention x time (p<0.05); different from baseline (p<0.05).
Figure 3.
Figure 3.
Absolute superficial femoral artery diameter (mm) at baseline and in response to exercise and water immersion. Bars represent group mean, error bars are SE, gray lines are individual data. * interaction: intervention x time (p < 0.05); different from baseline (p < 0.05).
Figure 4.
Figure 4.
Individual absolute change in superficial femoral artery flow-mediated dilation (FMD, %) in response to exercise and water immersion.

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