Nutrition Considerations for Ultra Endurance Sport, Pt 2: Hydration

Dehydration often contributes to both fatigue and GI symptoms during an ultra endurance event. Simply starting the event in a dehydrated state can set an athlete up for impaired performance, higher than expected perceived exertion (RPE), and a greater likelihood of GI distress. However, overhydration can also lead to GI symptoms and hyponatremia. Therefore, the safest hydration strategy for ultrarunners and cyclists is to drink appropriate temperature fluids (cool fluids in hot conditions, warmer fluids as possible in extreme cold) to thirst, practicing during training in preparation for the main event.

It is normal to expect water loss during exercise as a result of fuel oxidation (or loss of glycogen). During an ultra event, the water loss associated with glycogen likely exceeds 2% body mass suggesting that the common recommendation to avoid >2% body mass loss during ultra events may not be practical; and, in fact, can result in overhydration. Furthermore, appropriate fluid intake will vary with exercise intensity and environmental conditions.

While ultra athletes can certainly use hypotonic carb-electrolyte sports drinks for hydration, it is advised to obtain most of their caloric needs through foods, some of which contain sodium. Supplementing with additional sodium is not typically necessary or recommended and the race diets of ultra athletes generally provide adequate sodium provided they are eating to “sodium appetite”. Interestingly, visible sodium losses on clothing and gear may not reflect a need for increased sodium intake, but instead appears to represent the athlete’s recent dietary intake of sodium.

Cramping may be caused by sodium imbalance, but recent research suggests that sodium/fluid intake is not typically the culprit and often cramps are a result of overexertion, lack of training on specific race terrain, or too high pace/effort compared to the athlete’s preparation.

PMID: 26102445, 30056753, 30056755

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