Perturbed energy balance and hydration status in ultra-endurance runners during a 24 h ultra-marathon

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Full Papers

Human and Clinical Nutrition

Abbreviations: BM, body mass; CON, control; FR, fast running; MET, metabolic equivalents; P_Osmol, plasma osmolality; P_V, plasma volume; SR, slow running; UER, ultra-endurance runners

The unique characteristics of ultra-marathon events have enticed endurance enthusiasts to attempt such challenges, as evidenced by the substantial growth of ultra-endurance sports over the past decade⁽¹⁾, and an increased number of single- and multi-stage ultra-endurance running events conducted worldwide (http://www.racingtheplanet.com). Even though the popularity of ultra-endurance running has risen, research into the physiological and metabolic demands of such an extreme sport is scarce⁽²⁾, with limited studies investigating the dietary habits, alongside nutritional and hydration status of ultra-runners during these events. To date, only one observational study has comprehensively assessed nutritional and hydration status along with the dietary intake of ultra-runners during a multi-stage ultra-marathon competition^(3,4), while other studies have mainly focused on the assessment of specific nutrient or hydration variables during shorter single-stage events^(5,6).

Previously, studies investigating the dietary habits of endurance runners during a mountain marathon⁽⁵⁾and a 225 km multi-stage ultra-marathon⁽³⁾have reported suboptimal carbohydrate intake, with the latter also reporting compromised energy intake throughout the competition. In both studies, the participants were not able to consume sufficient carbohydrates during running (31 and 24 g/h, respectively) to meet the benchmark recommendations^(7,8). Indeed, carbohydrate intakes of 30-60 g/h are advised for endurance sports⁽⁷⁾, with even higher levels (i.e. up to 90 g/h and a glucose:fructose ratio of 2:1) being advocated for exercise bouts lasting more than 3 h^(9,10). Such recommendations have been associated with improved oxidation efficiency, reduced fatigue and enhanced exercise performance⁽¹¹⁾. Moreover, the compromised total daily intakes of energy and carbohydrate observed in all ultra-runners during the multi-stage ultra-marathon event were found to be accompanied by pronounced levels of urinary ketones as the competition progressed and to be positively associated with the quality of recovery in between the stages⁽³⁾. Such findings...