Athletes who choose the trail over the treadmill don't get the benefit of a thermostat. For much of the year in much of the United States, they are forced to contend with bitter cold and sweltering heat. But only recently have sports scientists zeroed in on exactly how those extreme temperatures influence performance.
"The biggest breakthroughs have come in the past five years," says Jim Cotter, Ph.D., a senior lecturer at the School of Physical Education at the University of Otago, in New Zealand. "We've learned that the optimal warm-up for cold weather exertion is quite different from the one you would carry out in the heat and, perhaps more important, that the skin and brain play larger than expected roles in determining how athletes respond to temperature changes."
The brain, scientists have discovered, can actually anticipate changes in body temperature and will adjust exercise intensity accordingly. This subconscious calculation takes into account both the outside temperature and the duration of the effort, and explains why slowdowns are almost automatic in the heat, even before signs of significant muscle fatigue set in.
If an athlete attempts to exercise beyond the brain's wishes, the cerebrum will respond by generating brutal sensations of exhaustion (i.e., heat strain). The sad fact: Ambient temperatures can trump your hard-earned fitness. Fortunately, though, researchers have developed strategies to help athletes stabilize their core temps in both hot and frigid conditions. Here are scientifically-backed tips to help you perform optimally in four temperature zones.
How to conquer any climate
Below 45°F (7°C)
The human body has limited physiological defenses for the cold. To maintain an optimal core temp, layer clothing properly (see The Science of Warmth ). Also, be sure that your muscles are well stocked with glycogen (fat metabolism is impaired at low temperatures) by consuming up to four grams of carbohydrates per pound of body weight daily and, during exercise, feeding your muscles extra carbs (about five to six ounces of sports drink every 15 minutes).
45°F to 50°F (7°C to 10°C)
This is the sweet spot for sustained exercise. Before long workouts, heat up your muscles by jogging or cycling slowly for 10 minutes and fire up your nervous system with a couple of 30-second bursts at close-to-maximal effort. During your warm-up and the first few miles of exercise, prevent shivering -- which can expend oxygen and promote fatigue -- by wearing layers that can be removed readily as you continue your workout.
50°F to 70°F (10°C to 21°C)
It's easier to get loose when it is 65 degrees (18 degrees Celsius) than when it's 35 (two degrees Celsius). And since musclecontraction velocity increases as sinews warm up, you can get into a groove right from the start of your workout. However, when exercising for 75 minutes or more, overheating is an issue. One study found that marathon times lengthen by 19 seconds for each degree above 55°F (13°C). Acclimatize by training in these temps for a week, and limit warm-ups to five minutes.
Above 70°F (21°C)
In warm temperatures, it's very difficult to shed excess body heat. Studies show that taking an ice-cold bath or relaxing in an air-conditioned room prior to exercise can up endurance by 37 percent for cyclists and 17 percent for runners. Training is important, too: When you work out for a week in the heat, you improve blood flow to the skin, lower the skin-temperature threshold for sweating and sweat more evenly, all of which allows you to exercise at a higher intensity for longer.