"When ultra-runners prepare for races that span hundreds of miles and last for days, they are not only challenging their determination and physical power. They are also exploring how far human physiology can be pushed. In a study published October 20 in the Cell Press journal Current Biology, researchers reported that even elite endurance athletes cannot consistently exceed an average "metabolic ceiling" equal to 2.5 times their basal metabolic rate (BMR) in daily energy use."
"The metabolic ceiling refers to the upper limit of calories a person can burn in a sustained way. Earlier studies suggested that people might reach up to 10 times their BMR, which is the minimum amount of energy needed while resting, but only for short, intense periods. Short bursts of six or seven times BMR are possible, but the body quickly pulls energy away from other functions to compensate, nudging athletes back toward the ceiling."
Ultra-runners, cyclists, and triathletes were monitored over weeks and months to measure long-term energy expenditure. The human body exhibits a sustained metabolic ceiling of about 2.5 times basal metabolic rate when averaged over days. Short, intense bursts reaching six to ten times BMR occur but cannot be maintained long-term. When activity spikes, the body reallocates energy away from other physiological functions to compensate, which pulls overall expenditure back toward the ceiling. The metabolic ceiling appears to be a hard biological limit on chronic energy output, constraining how much sustained activity humans can maintain.
Read at ScienceDaily
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