July: Fire

   You run at the edge of life, no exaggeration. All your lively lights and vitals function roughly within a 7-degree range of body heat. For example, your muscles work most efficiently when your temperature reaches a slightly fevered 101 degrees. Allow it to climb above 105 degrees, and you will perish. Between these 4 ticks on the thermometer lie a perfect marathon and a grave.

   We give scant notice to the miracle of our body's cooling systems, which manage this equilibrium even when outside temperatures vary by 80 degrees or more. Cooling is the essential problem for runners. Your muscles stoke a fierce inferno, which is why the only hard advice for running in subfreezing weather is to seek warm shelter soon after your workout ends and to keep your extremities covered. Don't forget your mittens.

   Hot weather, on the other hand, wants you dead. There's no fighting the heat; accommodation is your only hope. Your body will manage cooling automatically through the evaporation of sweat. As the saying goes, human beings are ugly bags of mostly water - some 60 percent of our physical makeup is liquid - so it's no surprise the body bails hot fluid to stay cool. Trouble is, perspiration is drawn from blood plasma. Over a long workout on a hot day, your blood thickens like sludgy motor oil, reducing its efficiency at piping oxygen to your muscles and hauling waste products away. You get slower, you get tired, you eventually collapse of heat exhaustion.

   This is why you want to hydrate well in advance of a hot day's race or workout and to continue sucking down fluids well afterward. Runners lose up to 1 liter of sweat per hour. Unfortunately, hydration is a local train, not an express: liquids must travel through your stomach, intestines, kidneys, and so forth before they do their magic. A swig of Gatorade won't instantly set you right, even if it makes a parched throat happy.

   Acclimation is another way to accommodate the heat, though racers tend to be excessive in this regard (as in everything else). You needn't do push-ups in the sauna or sprint up mountains under a blazing midday sun. The best research shows that your body adjusts within 10 to 14 days of running in hot climates. Gradually increase the length of your hot-weather workouts. You'll begin sweating - and therefore cooling - at a lower temperature. You'll lose more fluid but fewer electrolytes, the chemicals that hasten your body's absorption of liquids. Taste your skin after a workout; if it's not salty, then you've acclimated.

   It's also important to face the stubborn reality of heat. Runners simply don't perform as well in hot weather - neither for speed nor endurance. World records seldom fall in tropical climes. Summer workouts are enervating. Be realistic about the heat. Summer is a good time to seek new satisfactions in your workouts, new goals. Don't fight the sun.