To perform well, a warm clime takes time

Running & FitNews, July-August, 2003

if you run in a region with changing seasons, even though summer is in full swing, your body may not be. Researchers in France took nine triathletes to the tropics to examine the acclimatization process, and found after 14 days these well-trained athletes still showed climate-induced impairment of physiological responses and performance.

Though the subjects' mean temperature before, during and after exercise was significantly lower on day 14 than it was on day two (the first of the tropics trials), it was always higher in the tropics than it had been before they left (baseline). Mean heart rate was 153 bpm on day two, as opposed to 134 at baseline. The maximum speed subjects could maintain running on a treadmill for one minute was significantly lower in all three tropical trials: on day two, it was a full km/hr slower than at baseline. Anyone who has gone running on the first hot day of the year has experienced the body's initial discomfort with warm temperatures and humidity. The same goes for early-winter runs, which seem to punish the lungs as much as they do exposed extremities. Don't overdo it at the onset of a seasonal shift; be flexible. If you are supposed to run six miles and feel truly awful in the summer heat, call it after two or three. Avoid the hottest part of the day whenever possible. Take your cell phone with you and if you get caught out on a long run, contact a friend for a ride. If you live in a city, bring subway or cab fare. Though by day 14 the tropics runners were performing just less than one-quarter km/hr slower than they had been at home, the adaptation was still insufficient to indicate complete acclimatization even after two weeks.

(Can. J. Appl. Physiol., 2002, Vol. 27, No. 6, pp. 551-562)