August: Simmer

   The best tool a runner can take into summer's oven is low expectations. You can't beat the heat. Adapt? Yes. Plan? It's mortally necessary. But for all your calculations, your performance, in both speed and endurance, will suffer in high heat.

   It's not just you. Average marathon times drop as temperatures and humidity spike. World records in any event rarely fall on simmering days. Elite athletes know they're battling the sun as much as their closest competitors in high heat. Slower runners suffer the most, perhaps because they're under the broiler longer. In racing, packs of runners trap heat, making matters worse. Even casual workouts will feel leaden and enervating.

   Your body cools through the evaporation of sweat, which is transported to your skin through your blood. On sultry days, your muscles are competing with your skin for that blood. Muscles lose; otherwise you would perish. Also, as your core temperature rises, muscle enzymes burn glycogen more rapidly, depleting stores of the fuel that running requires. Your body simply isn't an efficient machine in the heat.

   You acclimate - and relatively quickly - though this varies with the individual runner. In as little as seven days, your blood volume expands, reducing the strain on your heart as it services the needs of both cooling and muscles. Sweat increases, and runners who have acclimated sweat sooner and more profusely. Incidentally, there's good evidence that your body continues to adapt throughout the warm season.

   Workouts aren't the only times your body acclimates to the heat. Walking, yard work, cleaning out the garage (you needn't be in full sun), or anything else that makes you break a sweat will speed the process. If you're using treadmills or weights, extra layers of clothing will help. In the meantime, when you run in hot-weather months, aim for duration rather than intensity. You can increase intensity once your body is used to the heat.

   Even after you've acclimated, you have to plan for summer's sizzle - much more so than for freezing weather. Runners should heed not only the temperature but also the humidity, which inhibits the evaporation of sweat. Get in the habit of drinking water before and after workouts, and also throughout the day. You may need to move your regular run to morning or evening hours when it's cooler. A treadmill is a smart alternative on sweltering days when air quality is poor. Hot months offer a good excuse to change your route so you have a leafy canopy overhead or so you're running along a body of water, where it's typically cooler, Maybe it's time to rethink your running clothes.

   Planning, like acclimation, takes you only so far, however. Ultimately, hot-weather months should change your thinking and sometimes your goals. Consider it a welcome break. The languid months bring other diversions that can help maintain aerobic fitness (swimming, for example). Leave speed and endurance for cooler seasons. Give summer its due.