title: Substantive hemodynamic and thermal strain upon completing lower-limb hot-water immersion; comparisons with treadmill running.
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-1vs. 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.
authors.affiliation: Department of Surgical Sciences, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand; School of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin, New Zealand.
authors.forename: Kate N
authors.initials: KN
authors.lastname: Thomas
authors.affiliation: Department of Surgical Sciences, Dunedin School of Medicine, University of Otago , Dunedin, New Zealand.
authors.forename: André M
authors.initials: AM
authors.lastname: van Rij
authors.affiliation: Department of Physiology, University of Otago, Dunedin, New Zealand; School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK.
authors.forename: Samuel J E
authors.initials: SJ
authors.lastname: Lucas
authors.affiliation: Department of Preventive and Social Medicine, University of Otago , Dunedin, New Zealand.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Gray
authors.affiliation: School of Physical Education, Sport and Exercise Sciences, University of Otago , Dunedin, New Zealand.
authors.forename: James D
authors.initials: JD
authors.lastname: Cotter
keywords: acute exercise; immersion; lower-limb heating; passive heat; shear stress