Energy balance
Ultra-endurance athletes can successfully complete multi-day events despite consuming only 36-54% of their estimated energy expenditure, primarily by shifting substrate oxidation toward fat and relying on gluconeogenesis to maintain blood glucose.
If you are training for long-duration events, do not expect to eat enough to match your calorie burn. Your body will adapt to burn fat and preserve glucose. Focus on tolerating food during breaks rather than hitting specific calorie targets, as appetite suppression is a natural physiological response to prolonged exercise.
SG primarily oxidised fat throughout the event (RER: 0.8 ± 0.03)... The main reasons for fatigue in ultra-running are most likely central fatigue, thermal stress, muscle damage, and/or limited endogenous muscle glycogen content and blood glucose availability... It was hypothesised that as well as energy derived from CHO and fat metabolism, a substantial provision came from lactate and gluconeogenesis.
Why this rating
Single case study (n=1); high internal validity for the subject but low generalizability.
Source
Physiological Responses and Nutritional Intake during a 7-Day Treadmill Running World Record
Nicolas Berger et al. · International Journal of Environmental Research and Public Health · 2020
DOI 10.3390/ijerph17165962
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