Cold Water Ingestion Improves Exercise Tolerance of Heat-Sensitive People with MS

Head and neck cooling enhance exercise tolerance in individuals with multiple sclerosis

BACKGROUND

Individuals with Multiple Sclerosis (MS) experience impairments in heat dissipation, compromising core temperature regulation during exercise.

OBJECTIVE

To examine the efficacy of combined head-and-neck cooling as administered via a commercially available cooling cap and neck wrap in mitigating increases in core temperature during exercise.

METHODS

On separate days, ten (7 females) adults (46.1 ± 11.6 years) with relapsing-remitting MS performed semi-recumbent cycling consisting of an incremental exercise bout to volitional fatigue in a temperate environment (23 °C, 50 % relative humidity) while undergoing head-and-neck cooling using a cooling cap and neck wrap maintained at 10 °C (COLD) or 24-26 °C (NEUTRAL). Prior to and following a 30-minute post-exercise recovery, functional capacity was assessed by a battery of tests consisting of a 2-minute walk test, Timed 25-Foot Walk test, sit-to-stand test, and Berg Balance Scale. Core (ingestible pill) and skin temperatures were recorded continuously. The level of fatigue was measured with questionnaires.

RESULTS

The duration of the incremental exercise test increased with the application of COLD (28.4 ± 5.1 min) versus NEUTRAL water (vs 20.8 ± 5.1 min) (p = 0.001) and was paralleled by a significant reduction in body temperatures (∼1 °C, p < 0.05). The distance covered during the 2-min walk test performed after the incremental exercise test increased with the COLD (176.5 ± 0.6 m), relative to the NEUTRAL condition (147.7 ± 43.5 m) (p = 0.01). Fatigue levels did not change between conditions.

CONCLUSION

We show that head-and-neck cooling with cold water effectively enhances exercise tolerance and mitigates increases in core temperature during exercise in individuals with MS.

Exercise-induced heat sensitivity in patients with multiple sclerosis: Definition, prevalence, etiology, and management-A scoping review

BACKGROUND

For persons with multiple sclerosis (pwMS), exercise is known to be safe and effective at treating several symptoms and it may even be disease-modifying. However, exercise can trigger heat intolerance, exercise-induced heat sensitivity (EIHS), which may cause some pwMS to refrain from exercise. No review has yet summarized the existing knowledge on EIHS in pwMS. Therefore, the purpose of the present review was to clarify the terminology, summarize both the prevalence of EIHS and the current knowledge of underlying mechanisms, and provide an overview of existing treatment options and clinical management of EIHS in pwMS.

METHODS

A scoping review was performed.

RESULTS

As no clear definition could be identified in the literature, we propose a definition of EIHS. Aspects related to EIHS are reported in 29-80 % of all pwMS. The mechanisms underlying EIHS are not well understood but seem to include axon demyelination, CNS lesions, abnormal sudomotor function and sweating, abnormal afferent thermosensory function, disease stability, and abnormal neuropsychological responses. The severity of EIHS depends on the applied exercise modality, intensity, and format, and can be further reduced when applying different cooling interventions or garments before and/or during exercise.

CONCLUSION

EIHS appears frequently in pwMS, but the underlying mechanisms are still only sparsely understood. EIHS severity depends on exercise-related factors and can be reduced by cooling interventions.

The effect of cooling garments to improve physical function in people with multiple sclerosis: A systematic review and meta-analysis

BACKGROUND

There is strong evidence for the benefits of exercise for people with Multiple Sclerosis (MS), however, up to 80% of people with MS report experiencing exacerbated symptoms with elevated body temperatures. A range of cooling garments to assist people with MS manage symptoms of heat sensitivity have been investigated. Therefore, the aim of this systematic review was to assess the effect of cooling garments to improve physical function in people with MS, and to determine any associated physiological and perceptual responses.

METHOD

A systematic review adhering to the PRISMA guidelines was performed. The eligibility criteria required investigations to have conducted a randomized controlled trial or cross-over study to assess the effect of a cooling garment to improve physical function, or a related physiological or perceptual measure, in people with MS.

RESULTS

Thirteen empirical studies were identified, compromising of acute cross-over designs (61.5%), longitudinal parallel group designs (23.1%) or a combination of both (15.4%). The studies included 384 participants with MS with an expanded disability status scale range of 1-7.5. Garments included liquid-perfused cooling vests/tops/hoods (50.0%), phase-change cooling vests (38.9%), a cooling thigh-cuff (5.6%) and a palm cooling device (5.6%). The cooling garments were effective at improving walking capacity and functional mobility, and some studies demonstrated improvements in muscular strength and balance, but not manual dexterity. The garments also resulted in improved core temperature, skin temperature, thermal sensation and subjective fatigue. Improvements occurred in temperate and warm conditions, and both with and without an exercise stimulus.

DISCUSSION

Cooling garments can improve physical function for people with MS. Since none of the cooling garments caused harm, and no particular cooling garment could be identified as being superior, people with MS should experiment with different cooling garments to determine their preference, and industry should focus on cooling garments that are effective, accessible and user-friendly.

Autonomic nervous system disorders in multiple sclerosis

Multiple sclerosis (MS) is a chronic progressive demyelinating disease of the central nervous system (CNS), which also affects the autonomic nervous system (ANS). Manifestations of MS in the ANS include urological, sexual, gastrointestinal, cardiovascular, and thermoregulatory disorders as well as increased fatigue. These problems are common yet are often underestimated due to the non-specificity of the symptoms and the limited evaluation of the ANS in the usual clinical practice. Most of these symptoms seem to be related to localized lesions in the CNS. However, the mechanisms by which these disorders are caused in MS have not been fully investigated, thus preventing any focused etiological treatment. The most common disorders of the ANS in MS represent a challenge for clinicians due to the variability of the clinical picture and our minimal data on their diagnosis and treatment. Early diagnosis and initiation of individualized treatment regimens, often in need of multiple approaches, seem to yield the best results in managing ANS dysfunction in MS patients.

The Effects of Cooling Therapies on Fatigue, Physical Activity, and Quality of Life in Multiple Sclerosis: A Meta-Analysis

PURPOSE

This meta-analysis examined the effects of the cooling therapies on fatigue, physical activity, and quality of life (QoL) in patients with multiple sclerosis (MS).

METHODS

Articles published between 2000 and 2020 were searched in six databases. The standardized mean differences were determined by the upper and lower limits of 95% confidence intervals. Publication bias was assessed by conducting the Egger test, which uses linear regression. Publication bias was examined visually using a funnel plot.

RESULTS

Nine studies were included in this meta-analysis. The types of cooling therapies included cooling garment (n = 4), cooling device (n = 2), cooling room (n = 1), precooling (n = 1), and cold water ingestion (n = 1). The results indicated a significant decrease in fatigue and an increase in physical activity following cooling therapy. Cooling therapies improved the QoL of patients with MS. The Egger test indicated no significant publication bias. However, the funnel plot presented a slight asymmetry among studies.

CONCLUSIONS AND CLINICAL RELEVANCE

Cooling therapies have a beneficial effect on fatigue, physical activity, and the QoL of patients with MS. Healthcare professionals can use cooling methods to manage thermosensitive symptoms in patients with MS.

Voluntary Cooling during Exercise Is Augmented in People with Multiple Sclerosis Who Experience Heat Sensitivity

INTRODUCTION

We tested the hypothesis that people with multiple sclerosis (MS) who experience heat sensitivity voluntarily engage in cool-seeking behavior during exercise to a greater extent than healthy controls.

METHODS

In a 27.0°C ± 0.2°C, 41% ± 2% RH environment, seven participants with relapsing-remitting MS who exhibited heat sensitivity and seven healthy controls completed two randomized trials cycling for 40 min (EX) at 3.5 W·kg-1 metabolic heat production, followed by 30 min recovery (REC). In one trial, participants were restricted from engaging in cooling (CON). In the other trial, participants voluntarily pressed a button to receive 2 min of ~2°C water perfusing a top (COOL). Mean skin and core temperatures and mean skin wettedness were recorded continuously. Total time in cooling provided an index of cool-seeking behavior. RPE, total symptom scores (MS only), and subjective fatigue (MS only) were recorded every 10 min.

RESULTS

Core temperature (+0.5°C ± 0.1°C) and skin wettedness (+0.53 ± 0.02 a.u.) increased but were not different between groups or trials at end exercise (P = 0.196) or end recovery (P = 0.342). Mean skin temperature was reduced in COOL compared with CON at end exercise (P ≤ 0.002), with no differences between groups (P ≥ 0.532). MS spent more total time in cooling during EX (MS, 13 ± 3 min; healthy, 7 ± 4 min; P < 0.001) but not REC (MS, 2 ± 1 min; healthy, 0 ± 1 min; P = 0.496). RPE was greater at end exercise in MS (P = 0.001). Total symptom scores increased during exercise (P = 0.005) but was not different between trials (P = 0.321), whereas subjective fatigue was not attenuated in the cooling trial (P = 0.065).

CONCLUSION

Voluntary cooling is augmented in MS but does not consistently mitigate perceptions of heat-related symptoms or subjective fatigue.

Exercise and Sports Science Australia (ESSA) position statement on exercise for people with mild to moderate multiple sclerosis

OBJECTIVES

Multiple sclerosis (MS), the most common chronic and progressive neurological condition of the central nervous system, affects 26,000 Australian adults. Exercise training has beneficial effects on MS-related impairments including reduced muscular strength, poor aerobic capacity and impaired mobility, and in consequence can improve quality of life. This Position Statement provides evidence-based recommendations for exercise prescription and delivery of exercise training for people with MS with mild to moderate disability.

DESIGN AND METHODS

Synthesis of published works within the field of exercise training in MS.

RESULTS

Exercise provides many benefits to people with MS. There is strong evidence that resistance and aerobic training, performed 2 to 3 times per week at a moderate intensity, are safe and can improve muscle strength, cardiorespiratory fitness, balance, fatigue, functional capacity, mobility and quality of life in people with MS with mild to moderate disability (Expanded Disease Severity Scale (EDSS) ≤ 6.5). However, the evidence for those with severe disability (EDSS >6.5) is less clear. The effects of exercise on MS pathogenesis, central nervous structures and other outcomes such as depression and cognitive impairment, have not been adequately investigated. Effective exercise interventions to improve balance, joint contractures and reduce falls in people with MS are also urgently needed as well as investigations of long-term (≥1 year) effects of exercise training.

CONCLUSIONS

Resistance and aerobic training exercises are effective to alleviate some characteristic signs and symptoms in MS and should be supplemented by balance exercise to prevent falls. Exercise training programs should be prescribed and delivered by qualified exercise professionals. It is important to recognise and accommodate exercise-associated complications such as fatigue and heat sensitivity.

Heat risk exacerbation potential for neurology patients during the COVID-19 pandemic and related isolation

COVID-19 may increase the risk of heat-related symptoms during hot weather since vulnerable populations, including the elderly and those with neurological disabilities, must continue to self-isolate, often indoors. Within the chronic neurological patient population, indoor conditions in summer months present a hazard because of impaired and/or altered thermoregulation, including poor hydration status due to both autonomic and behavioral dysfunction(s). To address this increased risk, telemedicine protocols should include an assessment of the patient's environmental parameters, and when combined with physiological data from wearable devices, identify those with neurological diseases who are at higher risk of heat illness. Personalized medicine during times of self-isolation must be encouraged, and using smart technology in ambient assisted living solutions, including e-health to monitor physiological parameters are highly recommended, not only during extreme weather conditions but also during times of increased isolation and vulnerability.

Physiological interactions with personal-protective clothing, physically demanding work and global warming: An Asia-Pacific perspective

The Asia-Pacific contains over half of the world's population, 21 countries have a Gross Domestic Product <25% of the world's largest economy, many countries have tropical climates and all suffer the impact of global warming. That 'perfect storm' exacerbates the risk of occupational heat illness, yet first responders must perform physically demanding work wearing personal-protective clothing and equipment. Unfortunately, the Eurocentric emphasis of past research has sometimes reduced its applicability to other ethnic groups. To redress that imbalance, relevant contemporary research has been reviewed, to which has been added information applicable to people of Asian, Melanesian and Polynesian ancestry. An epidemiological triad is used to identify the causal agents and host factors of work intolerance within hot-humid climates, commencing with the size dependency of resting metabolism and heat production accompanying load carriage, followed by a progression from the impact of single-layered clothing through to encapsulating ensembles. A morphological hypothesis is presented to account for inter-individual differences in heat production and heat loss, which seems to explain apparent ethnic- and gender-related differences in thermoregulation, at least within thermally compensable states. The mechanisms underlying work intolerance, cardiovascular insufficiency and heat illness are reviewed, along with epidemiological data from the Asia-Pacific. Finally, evidence-based preventative and treatment strategies are presented and updated concerning moisture-management fabrics and barriers, dehydration, pre- and post-exercise cooling, and heat adaptation. An extensive reference list is provided, with >25 recommendations enabling physiologists, occupational health specialists, policy makers, purchasing officers and manufacturers to rapidly extract interpretative outcomes pertinent to the Asia-Pacific.

Blunted sweating does not alter the rise in core temperature in people with multiple sclerosis exercising in the heat

The purpose of this study is to determine whether thermoregulatory capacity is altered by multiple sclerosis (MS) during exercise in the heat. Sixteen MS participants (EDSS: 2.9 ± 0.9; 47 ± 8 yr; 77.6 ± 14.0 kg) and 14 healthy control (CON) participants (43 ± 11 yr; 78.6 ± 17.0 kg) cycled at a heat production of 4 W·kg^-1 for 60 min at 30°C, 30% relative humidity (RH) (Warm). A subset of eight MS (EDSS: 2.6 ± 0.5; 44 ± 8 yr; 82.3 ± 18.2 kg) and 8 CON (44 ± 12 yr; 81.2 ± 21.1 kg) also exercised at 35°C, 30% RH (Hot). Rectal temperature (T_re), mean skin (T_sk) temperature, and local sweat rate (LSR) on the upper back (LSR_back) and forearm (LSR_arm) were measured. All CON, and only 9 of 16 and 7 of 8 MS participants completed 60 min of exercise in Warm and Hot trials, respectively. All MS participants who were unable to complete exercise stopped with a ΔT_re between 0.2 and 0.5°C. The time to reach a ΔT_re of 0.2°C was similar (MS: 28 ± 15 min, CON: 32 ± 18 min; P = 0.51). For MS participants, completing 60-min of exercise in Warm, ΔT_re (P = 0.13), ΔT_sk (P = 0.45), LSR_back (P = 0.69), and LSR_arm (P = 0.54) was similar to CON, but ΔT_b (body temperature) (MS: 0.16 ± 0.13°C, CON: 0.07 ± 0.06°C; P = 0.02) and onset time (MS: 16 ± 10 min, CON: 8 ± 5 min; P = 0.02) for sweating were greater in MS. Similarly, in Hot, ΔT_re (P = 0.52), ΔT_sk (P = 0.06), LSR_back (P = 0.59), and LSR_arm (P = 0.08) were similar, but ΔT_b (MS: 0.19 ± 0.16°C, CON: 0.06 ± 0.04°C; P = 0.04) and onset time (MS: 13 ± 7 min, CON: 6 ± 3 min; P = 0.02) for sweating were greater in MS. Even at 35°C, a delayed sweating onset did not alter heat loss to sufficiently affect exercise-induced rises in core temperature. Heat intolerance with MS does not seem attributable to thermoregulatory impairments.

Autonomic dysfunctions in multiple sclerosis: Challenges of clinical practice (Review)

Multiple sclerosis, demyelinating, inflammatory, degenerative, and chronic disease, raises many challenges in terms of disease management. The autonomic nervous system is affected by neuroinflammation but also contributes to its maintenance and the evolution of the disease. Multiple sclerosis interfering with parasympathetic or sympathetic modulation may influence the immune response. Less attention is paid to autonomic dysfunctions, although they produce a serious impact on the quality of life. In addition to motor disabilities, patients also have non-motor dysfunctions. Regardless of its clinical forms, patients with multiple sclerosis may have autonomous disturbances such as bladder, sexual, cardiovascular, thermoregulatory, gastrointestinal dysfunction and fatigue. These must be identified based on medical history, clinical symptoms, and specific paraclinical tests. In addition to the multitude of immunomodulatory therapeutic agents that influence the progression of the disease, the therapy of autonomic dysfunctions remains difficult to address. However, their identification and treatment lead to increased quality of patient management and avoid complications of this disease.

Comfortable walking speed and energy cost of locomotion in patients with multiple sclerosis

Comfortable walking speed and energy cost of walking are physiological markers of metabolic activity during gait. People with multiple sclerosis are characterized by altered gait biomechanics and energetics, related to the degree of disability and spasticity, which lead to an increased energy cost of walking. Several studies concerning the energy cost of walking in multiple sclerosis have been published. Nevertheless, differences in protocols and characteristics of the sample have led to different outcomes. The aim of the present meta-analysis is to summarize results from studies with specific inclusion characteristics, and to present data about the comfortable walking speed and the energy cost of walking at that speed. Moreover, a detailed discussion of the potential mechanisms involved in the altered metabolic activity during exercise was included. A total of 19 studies were considered, 12 of which were also part of the quantitative analysis. Despite the strict selection process, high between-group heterogeneity was found for both outcomes. Nevertheless, the overall results suggest a pooled mean comfortable walking speed of 1.12 m/s (95% CI 1.05-1.18) and energy cost of 0.19 mLO₂/kg/m (95% CI 0.17-0.21). These findings support the results of previous studies suggesting that energy cost of walking may be increased by 2-3 times compared to healthy controls (HC), and encourage the use of this marker in association with other parameters of the disease.

Impaired Thermoregulatory Function during Dynamic Exercise in Multiple Sclerosis

INTRODUCTION

Impairments in sudomotor function during passive whole-body heating have been reported in multiple sclerosis (MS), a demyelinating disease of the CNS that disrupts autonomic function. However, the capability of the thermoregulatory system to control body temperature during exercise has never been assessed in MS. Thus, the aim of the present study was to test the hypothesis that thermoregulatory function is impaired in MS patients compared with healthy controls (CON) exercising at similar rates of metabolic heat production.

METHODS

Sweating and skin blood flow responses were compared between 12 individuals diagnosed with relapsing-remitting MS (9 females, 3 males) and 12 sex-, age-, mass-, and BSA-matched CON during a single bout of cycling exercise (rate of metabolic heat production: ∼4.5 W·kg) for 60 min in a climate-controlled room (25°C, 30% RH).

RESULTS

Individuals with MS exhibited an attenuated increase in cumulative whole-body sweat loss after 30 min (MS, 72 ± 51 g; CON, 104 ± 37 g; P = 0.04) and 60 min (MS, 209 ± 94 g; CON, 285 ± 62 g; P = 0.02), as well as lower sweating thermosensitivity (MS, 0.49 ± 0.26 mg·cm·min·°C; CON, 0.86 ± 0.30 mg·cm·min·°C; P = 0.049). Despite evidence for thermoregulatory dysfunction, there were no differences between MS and CON in esophageal or rectal temperatures at 30- or 60-min time points (P > 0.05). Cutaneous vasculature responses were also not different in MS compared with CON (P > 0.05).

CONCLUSION

Taken together, MS blunts sweating responses during exercise while cutaneous vasculature responses are preserved. Altered mechanisms of body temperature regulation in persons with MS may lead to temporary worsening of disease symptoms and limit exercise tolerance under more thermally challenging conditions.

Heat-related issues and practical applications for Paralympic athletes at Tokyo 2020

International sporting competitions, including the Paralympic Games, are increasingly being held in hot and/or humid environmental conditions. Thus, a greater emphasis is being placed on preparing athletes for the potentially challenging environmental conditions of the host cities, such as the upcoming Games in Tokyo in 2020. However, evidence-based practices are limited for the impairment groups that are eligible to compete in Paralympic sport. This review aims to provide an overview of heat-related issues for Paralympic athletes alongside current recommendations to reduce thermal strain and technological advancements in the lead up to the Tokyo 2020 Paralympic Games. When competing in challenging environmental conditions, a number of factors may contribute to an athlete's predisposition to heightened thermal strain. These include the characteristics of the sport itself (type, intensity, duration, modality, and environmental conditions), the complexity and severity of the impairment and classification of the athlete. For heat vulnerable Paralympic athletes, strategies such as the implementation of cooling methods and heat acclimation can be used to combat the increase in heat strain. At an organizational level, regulations and specific heat policies should be considered for several Paralympic sports. Both the utilization of individual strategies and specific heat health policies should be employed to ensure that Paralympics athletes' health and sporting performance are not negatively affected during the competition in the heat at the Tokyo 2020 Paralympic Games.

Efficacy of Various Cooling Techniques During Exercise in Persons With Spinal Cord Injury: A Pilot Crossover Intervention Study

Background: Decentralization of the sympathetic nervous system in persons with spinal cord injury (SCI) results in impaired vasomotor and sudomotor activity and, subsequently, impaired thermoregulatory capacity during exercise in the heat. Hyperthermia can be life-threatening and, as such, cooling interventions are needed to prevent this sequela. Objectives: To measure change in core temperature (ΔTC) over time during exercise in normothermic and high ambient heat conditions to compare thermoregulatory capacity in persons with varying degrees of intact vasomotor and sudomotor activity and to determine the efficacy of three cooling interventions in mitigating TC rise. Methods: Three persons participated: a 51-year-old with complete (AIS A) tetraplegia (TP), a 32-year-old with AIS A paraplegia (PP), and a 40-year-old without SCI (AB). Each exercised for 30 minutes on a wheelchair treadmill propelled at 30 revolutions per minute under five different conditions: (1) cool (C) = 75°F without cooling, (2) hot (H) = 90°F without cooling, (3) 90°F with cooling vest (CV), (4) 90°F with water spray (WS), and (5) 90°F with ice slurry ingestion (IS). ΔTC was compared for all conditions in all participants. Results: ΔTC in the C and H conditions was proportional to the neurological level of injury, with Tc rising highest in the TP followed by the PP then AB. WS was most efficacious at mitigating rise in TC followed by IS and CV in TP and PP. None of the cooling interventions provided an added TC cooling effect in AB. Conclusion: WS was most efficacious at mitigating rise in TC in TP>PP during exercise in the heat and should be studied in a larger SCI population.

Temperature sensitivity in multiple sclerosis: An overview of its impact on sensory and cognitive symptoms

Multiple sclerosis (MS) is an autoimmune neurodegenerative disease characterized by demyelination of the central nervous system (CNS). The exact cause of MS is still unknown; yet its incidence and prevalence rates are growing worldwide, making MS a significant public health challenge. The heterogeneous distribution of demyelination within and between MS patients translates in a complex and varied array of autonomic, motor, sensory and cognitive symptoms. Yet a unique aspect of MS is the highly prevalent (60-80%) temperature sensitivity of its sufferers, where neurological symptoms are temporarily exacerbated by environmental- or exercise-induced increases (or decreases) in body temperature. MS temperature sensitivity is primarily driven by temperature-dependent slowing or blocking of neural conduction within the CNS due to changes in internal (core) temperature; yet changes in skin temperature could also contribute to symptom exacerbation (e.g. during sunlight and warm ambient exposure). The impact of temperature sensitivity, and particularly of increases in core temperature, on autonomic (e.g. thermoregulatory/cardiovascular function) and motor symptoms (e.g. fatigue) is well described. However, less attention has been given to how increases (and decreases) in core and skin temperature affect sensory and cognitive symptoms. Furthermore, it remains uncertain whether changes in skin temperature alone could also trigger worsening of symptoms. Here we review the impact of temperature sensitivity on MS sensory and cognitive function and discuss additional factors (e.g. changes in skin temperature) that potentially contribute to temperature-induced worsening of symptoms in the absence of alteration in core temperature.

Thermoregulatory dysfunction in multiple sclerosis

Multiple sclerosis (MS) is a progressive neurologic disorder that disrupts axonal myelin in the central nervous system. Demyelination produces alterations in saltatory conduction, slowed conduction velocity, and a predisposition to conduction block. An estimated 60-80% of MS patients experience temporary worsening of clinical signs and neurologic symptoms with heat exposure (Uhthoff's phenomenon). This heat intolerance in MS is related to the detrimental effects of increased temperature on action potential propagation in demyelinated axons, resulting in conduction slowing and/or block. Additionally, MS may produce impaired neural control of autonomic and endocrine functions. Isolating and interpreting mechanisms responsible for autonomic dysfunction due to MS can be difficult as it may involve sensory impairments, altered neural integration within the central nervous system, impaired effector responses, or combinations of all of these factors. MS lesions occur in areas of the brain responsible for the control and regulation of body temperature and thermoregulatory effector responses, resulting in impaired neural control of sudomotor pathways or neural-induced changes in eccrine sweat glands, as evidenced by observations of reduced sweating responses in MS patients. Although not comprehensive, some evidence exists concerning treatments (cooling, precooling, and pharmacologic) for the MS patient to preserve function and decrease symptom worsening during heat stress. This review focuses on four main themes influencing current understanding of thermoregulatory dysfunction in MS: (1) heat intolerance; (2) central regulation of body temperature; (3) thermoregulatory effector responses; and (4) countermeasures to improve or maintain function during thermal stress.