Research
Energy balance
Ultra-marathon running causes a significant energy deficit leading to reductions in both body fat and skeletal muscle mass.
If you are preparing for an ultra-marathon, expect to lose some muscle and fat due to the massive energy expenditure. To minimize muscle loss, prioritize high carbohydrate intake during the race and ensure adequate protein intake in the days following the event to support recovery.
GoodSupportsHIGH confidence
An ultra-marathon leads to an energy deficit resulting in a reduction of both body fat and skeletal muscle mass.
Why this rating
The paper is a narrative review summarizing multiple studies, providing strong consensus evidence.
Source
Physiology and Pathophysiology in Ultra-Marathon Running
Beat Knechtle et al. · Frontiers in Physiology · 2018
DOI 10.3389/fphys.2018.00634
narrative_reviewCited 309×
Read the paper DOI resolved against Crossref · corpus check 2026-06-10
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- Ultra-marathon running can lead to temporary pathological changes in organ systems, including the heart, liver, kidneys, and immune system, which typically normalize after the race.Good
- Previous race experience, specifically the number of ultra-marathon finishes and personal best marathon time, is the most important predictor of successful ultra-marathon performance.Good
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