Extreme energy expenditure during a 200 km three-day open-water swim: A doubly labeled water case study
Study Details
This case study used doubly labelled water to measure energy expenditure during a 200-km open-water swim completed over 73.5 hours by a 103-kg former Olympic-level swimmer 🔍
Key Findings
🔥 Total energy expenditure averaged 14,747 kcal/day, reaching approximately 46,600 kcal across the 76-hour measurement period
📈 This equated to 6.17 times basal metabolic rate, placing it among the highest directly measured sustained energy expenditures reported over a similar duration
🌊 The swim took place in 20.5°C water, where continuous conductive heat loss likely added substantially to the metabolic cost of near-continuous swimming
🥣 The athlete consumed around 10,000 kcal/day, using gels, bananas, muesli bars, sports drinks and larger meals approximately every 4 hours
📉 Despite this, the estimated cumulative energy deficit was still approximately 16,600 kcal
⏱️ Nutrition was provided every 20 minutes during brief stops, helping maintain intake without substantially interrupting progress
💧 Daily water turnover reached 14.8 L, equivalent to approximately 0.61 L/hour
💪 The athlete completed an estimated 200,000 strokes, contributing to shoulder pain, blisters and substantial upper-body mechanical stress
😴 Total rest time was around 7 hours, including partial sleep, across the event
↩️ A previous attempt ended after 163 km and 55 hours, when intake was only ~5700 kcal/day and sleep totalled around 40 minutes
⚠️ This involved one athlete, and calculating expenditure required assumptions about respiratory exchange ratio, so the exact values remain uncertain
Conclusion
For extreme multi-day endurance events, success depends not only on physical capacity, but on sustaining very high energy intake alongside realistic pacing, planned sleep, thermal protection and frequent, practical feeding opportunities ✅
Reference
https://www.sciencedirect.com/science/article/pii/S1728869X26000894?via%3Dihub
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