Even Elite Athletes Can't Exceed This Fundamental Metabolic Limit

"Yet elite endurance athletes are constantly pushing these biological boundaries. Now a new study that followed ultramarathon runners for up to a year suggests an answer. The research, published today in Current Biology, showed that ultramarathoners can burn an astounding 11,000 calories per day during competition. But they can't keep up these efforts for longand they pay a price for doing so."

"The study builds on decades of research aimed at determining the human body's metabolic ceilingthe maximum sustained rate of calories our bodies can tolerate burning. Foundational research from the 1980s and 1990s based on the 23-day Tour de France bike race set that limit at four to five times a person's basal metabolic rate (BMR), defined as the energy required to maintain the body at rest."

Research tracking ultramarathon runners for up to a year recorded energy expenditures reaching about 11,000 calories per day during competition. Such extreme caloric burn cannot be maintained long-term and leads to physiological costs. Historical research from the Tour de France estimated a ceiling at four to five times basal metabolic rate (BMR). Shorter events showed athletes reaching about 9.4 times BMR in 11-hour Ironman races and about 8.5 times BMR in 25-hour ultramarathons. Scientists proposed a duration-dependent metabolic ceiling: very high burn rates occur in short bursts, while average metabolic rate over training and competition appears limited to about 2.5 times BMR.

Read at www.scientificamerican.com