Researchers tracked 14 world-class endurance athletes for 52 weeks and found humans have a metabolic limit even elite fitness cannot overcome. The study, published in Current Biology, used doubly labeled water measurements on 12 male and two female ultra-endurance competitors averaging 37 years old. Lead author Andrew Best of Massachusetts College of Liberal Arts discovered athletes consistently averaged 2.5 times their resting metabolism over extended periods, never exceeding this ceiling. During brief efforts, one runner hit 7.08 times his basal rate over 23.5 hours, but longer durations showed predictable drops. At one week, athletes averaged 3.75 times resting metabolism, falling to 2.39 times at 52 weeks. During extreme training, virtually all energy above resting levels went to the sport itself, with other bodily functions shutting down to conserve energy. (Story URL)
