Having a sound but flexible hydration strategy is extremely important, as fluid intake is all about balancing fluid deficit (greater than 2% loss in body mass = reduced work capacity and performance) against fluid overload (hyponatremia). Hyponatremia is a potential life-threatening scenario resulting in over hydration and subsequent dilution and reduction in sodium levels, causing fatigue, nausea, vomiting, dizziness, alteration in consciousness (1).
Fluid loss will occur due to respiration, sweat (1-1.5L/hr, higher in hot weather) and urination (2,3). The degree to which this occurs is dependent on a multitude of variables, including terrain and gradient (effort required), temperature, genetics (heavy sweaters), training/tolerance, duration of the event. For those competing at altitude this also needs to be factored into the hydration strategy as higher altitude increases the risk of fluid loss due to, cold induced diuresis (similar to the diuretic effects of caffeine), hyperventilation (higher respiratory rate due to the lower oxygen levels) and the dry environment at altitude (4).
There are currently two schools of thought with hydration; drink to a plan 600-800 ml per hour but not greater than 800 ml per hour or drink to thirst (5). Both have arguments for and against but until such time as there is clear evidence in support of one approach over another, drinking to thirst while not straying too far from the 600-800 ml per hour recommendations is a reasonable strategy (5).
Choosing what to drink becomes the next question, water, hypertonic, hypotonic or isotonic solutions?
- Hypertonic drinks such as “Gatorade” contain higher concentrations of sugar and salt than the body.
- Hypotonic drinks such as “Mizone” contain lowers concentrations of sugar and salt than the body.
- Isotonic drinks such as “Powerade” contain similar concentrations of sugar and salt to the body.
Hypotonic drinks have been shown to be slightly more beneficial and improve performance through faster absorption in endurance athletes (6). However, if fluid loss is less than fluid intake while drinking isotonic fluids it will accelerate the dilution of sodium potentially resulting in hyponatremia (6). It is therefore important that a variety of fluid solutions is used during competition including, water, hypotonic and hypertonic drinks. For those who experience gastrointestinal upset during training or competition using a hypertonic fluid solution as a mouth rinse (don’t swallow the solution), can help to improve performance and reduce the sense of fatigue. While using water and electrolyte tablets to maintain sodium and fluid levels. Some athletes, especially in endurance sports find ginger can help reduce or prevent an upset stomach.