Does Cold Water or Ice Slurry Ingestion During Exercise Elicit a Net Body Cooling Effect in the Heat?

Abstract

Cold water or ice slurry ingestion during exercise seems to be an effective and practical means to improve endurance exercise performance in the heat. However, transient reductions in sweating appear to decrease the potential for evaporative heat loss from the skin by a magnitude that at least negates the additional internal heat loss as a cold ingested fluid warms up to equilibrate with body temperature; thus explaining equivalent core temperatures during exercise at a fixed heat production irrespective of the ingested fluid temperature. Internal heat transfer with cold fluid/ice is always 100% efficient; therefore, when a decrement occurs in the efficiency that sweat evaporates from the skin surface (i.e. sweating efficiency), a net cooling effect should begin to develop. Using established relationships between activity, climate and sweating efficiency, the boundary conditions beyond which cold ingested fluids are beneficial in terms of increasing net heat loss can be calculated. These conditions are warmer and more humid for cycling relative to running by virtue of the greater skin surface airflow, which promotes evaporation, for a given metabolic heat production and thus sweat rate. Within these boundary conditions, athletes should ingest fluids at the temperature they find most palatable, which likely varies from athlete to athlete, and therefore best maintain hydration status. The cooling benefits of cold fluid/ice ingestion during exercise are likely disproportionately greater for athletes with physiological disruptions to sweating, such as those with a spinal cord injury or burn injuries, as their capacity for skin surface evaporative heat loss is much lower; however, more research examining these groups is needed.

Contemporary Nutrition Strategies to Optimize Performance in Distance Runners and Race Walkers

“…Here, we note that glycerol has been removed from the World Anti-Doping Agency's list of prohibited substances and may be reinstated for use in hyperhydration/rehydration strategies. The intake of ice slurries within precooling strategies to reduce prerace core temperature via the "heat sink" created by the phase change from ice to water may also be beneficial (Jay & Morris, 2018;Ross et al, 2013). Where in-race fluid intake is practical, mouth sensing of cold water or menthol may provide a sense of cooling during a race to reduce ratings of…”

“…perceived effort (Stevens & Best, 2017), while intake of reasonable amounts of cold/icy beverages might theoretically contribute to improved thermoregulation (Jay & Morris, 2018). The literature on the specific benefits of these strategies (see Table 6) in high-performance running or racewalking scenarios is sparse; an investigation is required, including the assessment of potential disadvantages such as an increase in BM or a greater risk of gut disturbances.…”

“…Ice slurry for precooling and within race cooling (for review, see Jay & Morris, 2018;Ross et al, 2013) Mechanism of action…”

Fluid Needs for Training, Competition, and Recovery in Track-and-Field Athletes

“…Various kinds of thermal management scenarios are possible, such as cold towels, ice vests, indoor (air conditioned) exercise, and early morning-or lateevening exercise. Ingestion of ice slurry before exercise is an alternative hydration strategy, but appears no more effective than cold water and may produce untoward side effects (Jay & Morris, 2018). The practice of trying to delay dehydration by expanding total body water using beverages with high salt concentrations or glycerol is generally ineffective and carries its own risks (McDermott et al, 2017).…”

Impact of Ice Slurry Ingestion During Break-Times on Repeated-Sprint Exercise in the Heat

“…However, it is speculated that the reduction of total sweat volume may appear to decrease the potential for evaporative heat loss from the skin. Jay and Morris [28] noted that this might not necessarily result in a net cooling effect. This cooling effect could be due to a reduction in sweating that lowers the evaporative heat loss from the skin by an amount that is at least equivalent to the additional internal heat loss with the ingested fluid.…”