Active Voice: In Warm Environments, A Cold Drink Improves Exercise Tolerance of Heat-Sensitive Multiple Sclerosis Patients By Ollie Jay, Ph.D., FACSM, and Georgia K. Chaseling, B.Sc. (Hons) Ollie Jay, Ph.D., FACSM Georgia K. Chaseling, B.Sc. (Hons) Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily represent positions or policies of ACSM. Ollie Jay, Ph.D., FACSM, is an associate professor of exercise and environmental physiology in the faculty of Health Sciences and is the director of the Thermal Ergonomics Laboratory at the University of Sydney, Australia. Ollie is also lead researcher of the Charles Perkins Centre research node on climate adaptation and health. Georgia Chaseling, B.Sc. (Hons), is a Ph.D. candidate at the Thermal Ergonomics Laboratory under the supervision of Dr. Jay and is a Multiple Sclerosis Research Australia Fellow. Georgia is a student member of ACSM. This commentary presents the authors’ views on the topic of their research article, which they and their colleagues authored. Their article appeared in the April 2018 issue of Medicine & Science in Sports & Exercise® (MSSE). Hot weather is particularly problematic for a large proportion of the 2.5 million people, worldwide, who live with multiple sclerosis (MS) and experience heat intolerance. Although we do not completely understand the underlying causes, it has been suggested that a rise in body temperature as little as 0.2 to 0.5°C can elicit heat intolerance — a situation often characterized by a rapid onset of fatigue for those with MS. For too long, clinicians and health professionals have advised MS patients to avoid physical activity or going outdoors to prevent exposure to the heat. Cooling strategies, such as wearing an ice vest or cooling collar, or spending long periods in a cold bath or shower, also are recommended before and during heat exposure. However, in the context of everyday life, these methods are largely impractical. The benefits of physical activity for people with MS are well established and, while we need to better understand the root causes of heat intolerance, finding simple and practical ways for people with MS to improve their capacity to remain physically active in the heat is an urgent priority. A study from our laboratory, as described in the April 2018 issue of MSSE, was sponsored by a Multiple Sclerosis Research Australia incubator grant. The work was conducted in collaboration with researchers from Southern Methodist University (Scott L. Davis, Ph.D.) and Loughborough University (Davide Filingeri, Ph.D.). Our objective was to investigate whether cold fluid ingestion improves exercise tolerance of people with MS in a hot environment (30°C, 30 percent RH). Ten MS and 10 control participants cycled on a semi-recumbent ergometer at a low relative intensity (40 percent of V?O2max) for 60 minutes (or until volitional exhaustion) on two separate occasions. In each trial, participants consumed approximately 250 ml of either 1.5°C or 37°C water every 15 minutes throughout exercise. The results from our study demonstrated three key findings: While only three of the 10 MS participants completed 60 minutes of exercise with a 37°C drink, all 10 age- and fitness-matched controls completed 60 minutes of exercise. This difference in exercise duration between groups was presumably due to the development of fatigue associated with heat intolerance; All seven MS participants who could not complete 60 minutes of cycling with the thermoneutral drink cycled longer with a cold drink — and, on average, MS participants cycled about 30 percent longer with cold water ingestion; Interestingly, the longer exercise duration that the MS participants achieved with a cold drink was not accompanied by a blunted rise in core or skin temperatures. This suggested heat-related reductions in exercise capacity in people with MS can be mitigated without the requirement of lowering core temperature. In conclusion, we cannot limit our understanding of heat intolerance in MS patients to the simple notion that a critical increase in core temperature is the only cause. These findings provide a practical and simple strategy for improving exercise capacity of people with MS in warm environments. Furthermore, the results from our research suggest that there may be other physiological and perceptual mechanisms that influence heat intolerance in MS patients, both of which require further investigation.