When you are dehydrated, your athletic abilities, including strength, endurance, coordination, mental acuity and thermoregulation, are decreased. Hyperhydration is a method created by Van Rosendal et al (1) aiming to increase body water content before exercise in case that dehydration cannot be prevented when starting from a state of euhydration (the normal state of body water content).
From this hyperhydrated status, athletes have a greater capacity to tolerate fluid loss before becoming dehydrated. Furthermore, excess pre-exercise fluid intake enhances thermoregulatory ability, as well as increasing blood plasma volume to maintain cardiac output.
A hyperhydrated status is difficult to create since a large fluid intake is typically accompanied by diuresis. However, glycerol-containing beverages can create an osmotic gradient in the circulation favoring fluid retention and facilitating hyperhydration. The recommend dose consuming in a period of 60 to 30 minutes before exercise is glycerol 1.2 g/kg (0.55 g/lb) BW in 26 ml/kg (0.4 oz/lb) BW of fluid. During exercise, taking glycerol 0.125 g/kg (0.06 g/lb) BW in 5 ml/kg (0.08 oz/lb) BW during may delay dehydration. After exercise, adding glycerol 1.0 g/kg (0.45 g/lb) BW to each 1.5 L (50 oz) of fluid will accelerate the restoration of plasma volume. For example, if your weight is 170 lb, take 5 tbsp of glycerol in 0.5 gallon of fluid before exercise, ½ tbsp in 14 oz of fluid during exercise and 4 tbsp in 50 oz of fluid after exercise.
Glycerol is a colorless, odorless, viscous liquid that is widely used as a sweetener, humectant and solvent in food and pharmaceutical industries. Possible side effects of Ingesting glycerol are nausea, GI discomfort and light–headedness.
Van Rosendal SP, Osborne MA, Fassett RG, Coombes JS, Guidelines for glycerol use in hyperhydration and rehydration associated with exercise. Sports Med. 2010, 1;40(2):113–29.