Optimising an ice-slurry beverage

Improved exercise performance with glycerol may not simply be explained by an attenuated body fluid deficit but may be the result of a reduction in deep body core temperature.

The use of internal pre-event cooling strategies, such as ice-slurries and cold beverages have been shown to increases the athlete’s capacity to store environmental and metabolic heat gained during exercise.

Glycerol’s ability to hydrogen-bond with water means that when a glycerol:water mixture is cooled it lowers the freezing point of the solution before ice starts to form, acting as an ‘anti-freeze’. The addition of glycerol (or other solutes, such as carbohydrate and/or sodium) to a hydration solution allows it to be served at sub-zero temperatures and improves its consistency so frozen beverage can be readily ingested using a straw.¹ A practical limitation may involve the discomfort associated with subsequent brain freeze (i.e., sphenopalatine ganglioneuralgia).

Considerations

• Since the timing of hyperhydration (90-180 min pre-exercise) and pre-cooling (30-60 min pre-exercise) strategies are implemented at different times prior to the start of exercise, the dose of glycerol can be split between the beverages but favouring the timing of delivery of the hyperhydration beverage. For instance, withhold 0.2 - 0.4 g/kg BM glycerol from the glycerol-based hyperhydration to add to the slushie.
• Explicit ingredient labelling is required if adding glycerol to an ice-slurry machine so other users are aware of the contents.