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The purpose of this study was to examine the effects of 6 weeks of localized, muscle-focused (quadriceps femoris) passive heat therapy (PHT) on resistance artery function, exercise haemodynamics and exercise performance relative to knee extension (KE) exercise training (EX). We randomized 34 healthy adults (ages 18-36; n = 17 female, 17 male) to receive either PHT or sham heating sessions (120 min, 3 days/week), or EX (40 min, 3 days/week) over 6 weeks. Blood flow was assessed with Doppler ultrasound of the femoral artery during both passive leg movement (PLM) and a KE graded exercise test. Muscle biopsies were taken from the vastus lateralis at baseline and after 6 weeks. Peak blood flow during PLM increased to the same extent in both the EX (∼10.5% increase, P = 0.009) and PHT groups (∼8.5% increase, P = 0.044). Peak flow during knee extension exercise increased in EX (∼19%, P = 0.005), but did not change in PHT (P = 0.523) and decreased in SHAM (∼7%, P = 0.020). Peak vascular conductance during KE increased by ∼25% in EX (P = 0.030) and PHT (P = 0.012). KE peak power increased in EX by ∼27% (P = 0.001) but did not significantly change in PHT and SHAM groups. Expression of endothelial nitric oxide synthase increased significantly in both EX (P = 0.028) and PHT (P = 0.0095), but only EX resulted in increased angiogenesis. In conclusion, 6 weeks of localized PHT improved resistance artery function at rest and during exercise to the same extent as exercise training but did not yield significant improvements in performance. KEY POINTS: Many for whom exercise would be most beneficial are either unable to exercise or have a very low exercise tolerance. In these cases, an alternative treatment to combat declines in resistance artery function is needed. We tested the hypothesis that passive heat therapy (PHT) would increase resistance artery function, improve exercise haemodynamics and enhance exercise performance compared to a sham treatment, but less than aerobic exercise training. This report shows that 6 weeks of localized PHT improved resistance artery function at rest and during exercise to the same extent as exercise training but did not improve exercise performance. Additionally, muscle biopsy analyses revealed that endothelial nitric oxide synthase expression increased in both PHT and exercise training groups, but only exercise resulted in increased angiogenesis. Our data demonstrate the efficacy of applying passive heat as an alternative treatment to improve resistance artery function for those unable to receive the benefits of regular exercise., (© 2024 The Authors. The Journal of Physiology © 2024 The Physiological Society.)

Sauna has been linked to a reduction of cardiovascular disease risk and is a promising nonpharmacological treatment for populations at risk of cardiovascular disease. This study examined the vascular response to an acute bout of sauna heating in young and middle-aged individuals. Ten young (25 ± 4 yr, 6 males and 4 females) and eight middle-aged adults (56 ± 4 yr, 4 males and 4 females) underwent 40 min of sauna exposure at 80°C. Esophageal and intramuscular temperatures, brachial and superficial femoral artery blood flow, artery diameter, and shear rates were recorded at baseline and following heat exposure. Brachial artery flow-mediated dilation (FMD) was measured at baseline and following 90 min of recovery. Esophageal and muscle temperatures increased similarly in the young and middle-aged adults by 1.5 ± 0.53 and 1.95 ± 0.70°C, respectively ( P < 0.05). The shear rate increased by 170-200% ( P < 0.001), while blood flow increased by 180-390% ( P < 0.001) in the superficial femoral and brachial arteries, respectively, and did not differ between age groups ( P = 0.190-0.899). Systolic blood pressure was reduced from 135 ± 17 to 122 ± 20 mmHg ( P = 0.017) in middle-aged participants. These data indicate that young and middle-aged adults have similar vascular responses to acute sauna heating. NEW & NOTEWORTHY Sauna therapy has been shown to improve cardiovascular health and function in older adults and individuals with cardiovascular disease risk factors. Specifically, improvements in vascular function have been reported and have been attributed to the increased hemodynamic stimuli on the vasculature associated with thermal stress. The present study quantified this hemodynamic response to a sauna protocol associated with improved cardiovascular health across the lifespan. Our data show that middle-aged adults have the same shear rate and blood flow response to sauna as young adults.

Few formulas have been used in exercise physiology as extensively as the Fick formula, which calculates the rate of oxygen consumption ( i.e. , V.O 2 ) as the product of cardiac output (Q.) and the difference in oxygen content in arterial and mixed venous blood (Δa v ¯ O 2 ). Unfortunately, the physiology of maximum V.O 2 (V.O 2MAX ) is often misinterpreted due to a lack of appreciation for the limitations represented by the oft-ignored superscript annotations in the Fick formula. The purpose of this perspective is to explain the meaning of the superscript annotations and highlight how such annotations influence proper interpretation of V.O 2MAX physiology with the Fick formula. First, we explain the significance of the overdots above V.O 2 and Q., which indicate a measure per unit of time. As we will show, the presence of an overdot above Q. and lack of one above Δa v ¯ O 2 denotes they are different types of ratios and should be interpreted in the context of one another-not in contrast to each other as is commonplace. Second, we discuss the significance of the overline above the " v ¯ " in Δa v ¯ O 2 , which indicates the venous sample is an average of blood that comes from mixed sources. The mixed nature of the venous sample has major implications for interpreting the influence of oxygen diffusion and blood flow heterogeneity on V.O 2MAX . Ultimately, we give recommendations and insights for using the Fick formula to calculate V.O 2 and interpret V.O 2MAX physiology., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Gifford, Blackmon, Hales, Hinkle and Richards.)

Ageing results in lower exercise tolerance, manifested as decreased critical power (CP). We examined whether the age-related decrease in CP occurs independently of changes in muscle mass and whether it is related to impaired vascular function. Ten older (63.1 ± 2.5 years) and 10 younger (24.4 ± 4.0 years) physically active volunteers participated. Physical activity was measured with accelerometry. Leg muscle mass was quantified with dual X-ray absorptiometry. The CP and maximum power during a graded exercise test (P GXT ) of single-leg knee-extension exercise were determined over the course of four visits. During a fifth visit, vascular function of the leg was assessed with passive leg movement (PLM) hyperaemia and leg blood flow and vascular conductance during knee-extension exercise at 10 W, 20 W, slightly below CP (90% CP) and P GXT . Despite not differing in leg lean mass (P = 0.901) and physical activity (e.g., steps per day, P = 0.735), older subjects had ∼30% lower mass-specific CP (old = 3.20 ± 0.94 W kg -1 vs. young = 4.60 ± 0.87 W kg -1 ; P < 0.001). The PLM-induced hyperaemia and leg blood flow and/or conductance were blunted in the old at 20 W, 90% CP and P GXT (P < 0.05). When normalized for leg muscle mass, CP was strongly correlated with PLM-induced hyperaemia (R 2  = 0.52; P < 0.001) and vascular conductance during knee-extension exercise at 20 W (R 2  = 0.34; P = 0.014) and 90% CP (R 2  = 0.39; P = 0.004). In conclusion, the age-related decline in CP is not only an issue of muscle quantity, but also of impaired muscle quality that corresponds to impaired vascular function., (© 2023 The Authors. Experimental Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society.)

The Tour Divide (TD) is a 4385 km ultra-endurance bicycle race that follows the continental divide from Canada to Mexico. In this case study, we performed a comprehensive molecular and physiological profile before and after the completion of the TD. Assessments were performed 35 days before the start (Pre-TD) and ∼36 h after the finish (Post-TD). Total energy expenditure was assessed during the first 9 days by doubly labelled water ( 2 H 2 18 O), abdominal and leg tissue volumes via MRI, and graded exercise tests to quantify fitness and substrate preference. Vastus lateralis muscle biopsies were taken to measure mitochondrial function via respirometry, and vascular function was assessed using Doppler ultrasound. The 47-year-old male subject took 16 days 7 h 45 min to complete the route. He rode an average of 16.8 h/day. Neither maximal O 2 uptake nor maximal power output changed pre- to post-TD. Measurement of total energy expenditure and dietary recall records suggested maintenance of energy balance, which was supported by the lack of change in body weight. The subject lost both appendicular and trunk fat mass and gained leg lean mass pre- to post-TD. Skeletal muscle mitochondrial and vascular endothelial function decreased pre- to post-TD. Overall, exercise performance was maintained despite reductions in muscle mitochondrial and vascular endothelial function post-TD, suggesting a metabolic reserve in our highly trained athlete., (© 2024 The Authors. Experimental Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society.)