Scientific Programme
Sports and Exercise Medicine and Health
IS-MH11 - How sauna learnt a lesson from the gym – the shared health benefits of passive heat exposure and exercise
Date: 05.07.2024, Time: 13:00 - 14:15, Lecture room: M1
Description
Aerobic exercise and the passive elevation of body temperature share several physiological responses. Both impact on glycaemic control, inflammation, blood pressure regulation, and sympathetic control. As a result, exercise and heat therapy can result in health benefits, including enhanced physical performance, reductions in resting blood pressure, improved autonomic function, and improvements to the cardiometabolic risk profile. Whilst the literature to date implies that exercise tends to result in larger health benefits than passive heating, heat therapy may be an alternative or adjunctive health promoting strategy to those unable to realise the health benefits of exercise. In this symposium we discuss the acute physiological changes and chronic adaptations to the passive elevation of body temperature across the health continuum. We outline shared pathways between heat and exercise interventions and discuss in which situations heat therapy may be preferrable to exercise interventions. Practical challenges for the implementation of heat therapy to improve population health will also be considered. The presenters have more than 35 years of shared experience in the field and debate the most recent primary data from their laboratories. The symposium will therefore offer current insight based on original data on a topic which has increasingly gained popularity – both in science as well as in the media.
Chair
Christof Leicht
Loughborough University, SSEHS
United Kingdom
ECSS Glasgow 2024: IS-MH11
Speaker A
Christof Leicht
Loughborough University, SSEHS
United Kingdom
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No pain, gain? Exploring strategies to enhance the tolerability of passive heating
While the prospect of sitting in a hot bath to increase body temperature is appealing to many, the perceptual responses to whole-body passive heating suggest that this activity can be accompanied by substantial thermal discomfort. Particularly the more dated studies investigating the acute physiological response and chronic adaptations to passive heating often employed protocols using temperatures and/or exposure durations that could be described as gruelling. Such intense protocols often resulted in the desired impact on health-related physiological outcomes, including an acute increase in inflammatory markers, decrease in blood pressure, or chronic reductions in resting blood pressure. However, more recent studies that also assessed qualitative participant feedback report statements such as ‘it was intensely hot’, or an outright ‘it was too uncomfortable’. This is problematic. Exercise studies outline the importance of the subjective experience for long-term adherence, an essential aspect to long-term health benefits. In this talk, I will focus on approaches to optimise the subjective experience to heat interventions. I will present studies that have explored the balance between tolerability and acute physiological responses to passive heating, with a focus on inflammatory markers, blood pressure regulation, and vascular control. Reducing skin temperature, either over large body segments or those areas particularly sensitive to heat, such as the face, is a promising approach. I will discuss the application of local cooling via conduction (e.g., ice pack application) and convection (e.g., fan exposure), and unpick thermophysiological differences between heating media (e.g., hot water immersion vs sauna). Particularly the cooling of small, sensitive areas appears promising, as the overall body temperature is, if at all, only minimally affected. This results in similar beneficial changes to health-related markers, whilst improving the subjective perceptive response. Cooling larger body areas, on the other hand, may come at the expense of health benefits by reducing overall heat gain. The importance of skin temperature is also evident when comparing modalities. For the same increase in core temperature, the subjective response to hot water immersion appears to be more positive compared with hot air exposure, which results in higher skin temperatures. In summary, whilst a sufficient heat stimulus is needed to induce beneficial adaptations, protocol adjustments by limiting the increase in skin temperature may increase comfort and therefore help long-term adherence.
Speaker B
Amy Harwood
Hull York Medical School, Rehabilitation Medicine
United Kingdom
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Moving passive heat therapy to the clinic – evidence for its feasibility and efficacy
Studies in able-bodied individuals indicate improvements in glucose tolerance, vascular function and the inflammatory profile following repeated passive heat exposure. These findings have encouraged translation to clinical populations. Indeed, disability- and chronic disease-specific alterations in physiological responses to thermal stress should be considered when investigating and aiming to implement passive heat therapy in such individuals. For example, the impaired thermoregulatory capacity in persons with spinal cord injury may limit the dose of exogeneous heat that can be prescribed. Nonetheless, preliminary studies show that passive heat therapy is feasible and tolerable in people from a range of clinical populations. Patients with peripheral arterial disease completed 99% of the prescribed lower-limb passive heating sessions during a 6-week trial. Those with coronary artery disease completed all prescribed whole-body heating sessions during a 2-week intervention and there was no difference in compliance between the passive heat therapy and exercise arms in persons with osteoarthritis. In our ongoing 8-week trial in persons with spinal cord injury, 6 out of 7 participants completed all prescribed passive heating sessions using heating blankets. However, reviewing the efficacy of chronic passive heat therapy to improve vascular, glycaemic and inflammatory outcomes paints a mixed picture. Flow mediated dilation was improved following daily sauna in persons with coronary artery disease. In contrast, reactive hyperaemia and arterial stiffness were not improved following sauna or lower-limb heating in those with peripheral artery disease. Nonetheless, a reduction in blood pressure appears a consistent finding across interventions and populations. Fasting measures of glucose tolerance are improved in females with polycystic ovary syndrome but not in persons with osteoarthritis following repeated hot water immersion. Assessing postprandial glucose tolerance through an oral glucose tolerance test, we found no improvement in glucose tolerance in individuals with spinal cord injury following repeated whole-body heating. The same held true for basal circulating inflammatory markers (interleukin (IL)-6, tumour necrosis factors-α, C-reactive protein). While the small-scale preliminary studies discussed here may have suffered from insufficient statistical power, the mixed results regarding the efficacy of heat therapy to improve glucose tolerance and chronic low-grade inflammation in clinical populations may also be related to the comparatively small doses of exogenous heat often employed. In summary, passive heat therapy is an attractive intervention for persons with a reduced physical capacity. While early studies support its feasibility, larger scale randomised controlled trials, possibly using more demanding heating protocols than employed thus far, are required to confirm its potential to improve metabolic health in clinical populations.
Speaker C
Ely Brett
Providence College, Department of Health Sciences
United States
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Post-exercise heat exposure to maximize health and performance benefits of exercise
This talk will discuss data from studies in athletes and clinical populations examining the acute impact of post-exercise heat exposure on cardiovascular and autonomic variables, including heart rate variability, nocturnal blood pressure, and blood flow. Examination of the shared and unique mechanisms and benefits of exercise and heat therapy allow for exploration of passive heat, exercise, and combined therapies to provide protocols targeted for individual performance goals or health conditions. In athletic populations, post-exercise passive heat exposure is used to enhance cardiorespiratory fitness and prepare for hot-weather competition. However, there are concerns that the added stress of acute heat exposure may delay recovery or impair short-term performance. Examining the autonomic recovery from interval exercise with or without post-exercise hot water immersion allows to assess whether a passive heat protocol can be implemented with minimal training interruptions. Our results indicate that there is no impact of post-exercise heat exposure on next-morning heart rate variability compared to exercise alone in trained individuals. In clinical populations, including those with an impaired ability to participate in vigorous exercise and individuals with elevated cardiovascular risk, heat therapy can improve autonomic function and blood pressure control. The combination of moderate exercise with post-exercise leg heating may be a practical solution to enhance the autonomic benefits of exercise. In a series of studies in individuals with hypertension and individuals with mobility limitations, we examined acute changes in blood flow, overnight blood pressure, and nocturnal heart rate variability in response to leg heating alone, exercise combined with leg heating, or exercise with thermoneutral leg immersion. The combination of exercise and leg heating resulted in the greatest increases in leg blood flow and the most substantial improvement in overnight blood pressure compared to either standalone treatment. In summary, post-exercise hot water immersion is well-tolerated in athletic and clinical populations and can enhance the acute cardiovascular benefits of exercise. Our data suggest that the individual health benefits for exercise and passive heating combine to maximize overall benefits across the health continuum.