The Journal of Sports Medicine and Physical Fitness offers some clues. Researchers in Brazil looked at five male recreational runners in their mid-30s, and measured their physiological responses to warm temperatures while running a long-distance race using a portable metabolic analyzer which measures oxygen consumption during activity. Researchers also tracked the runners’ cardiovascular responses, including their heart rate, and recorded their body temperatures with another device called a capsule telemetric system.
The sample size of the study was so small because of the amount of data gathered during the race, according to study co-author Danilo Prado, Ph.D., of the Ultra Sports Science Lab and University of São Paulo in Brazil. But despite the modest number of participants, he told