It’s still winter where I live, but if you’re planning on running early spring or summer races, preparing for running in the heat should be on your mind. There are lots of changes that occur in your body when you become adapted to the heat during exercise.
One of the first things is you have a lower heart rate when exercising at a particular temperature. Your blood plasma increases, which allows you to move warm blood toward the outside of your body to dissipate heat. Increased blood plasma also allows you to begin sweating earlier and at a higher rate. Sweating earlier means your body will start sweating when your core temperature goes up by one degree rather than two or three. This head start may not seem like much, but is important for maintaining a lower core temperature.
Without the increase in your plasma volume, you would compromise your cardiovascular output as more energy was shunted to decreasing your body temperature through sweat and moving your blood around.
Now keep in mind that just because you are more efficient at running in the heat, does not mean that you can slack off on your hydration. You are actually losing more fluid because you are sweating earlier and at an increased rate. The change in the amount of sweat lost can be huge. Normal fluid lost for one hour of exercise is 0.5 to 1 liter. As you become heat acclimated, this can increase up to 1-2 liters per hour.
How do you get ready for the heat? run in the heat. hot and humid is difficult to adapt to but you can do it to a point. If it’s winter or just not hot enough where you live, there are still some things you can do. The bottom line is you want to increase your core body temperature to about 100 to 101.5 degrees.
Some options include building a really simple heat chamber in your home, over dressing. If you have the space, create a room that gets really hot. You can use space heaters or stop the clothes dryer from ventilating outside (which will increase humidity too). Ideally, you’ll have a treadmill, but some other type of exercise equipment like a stationary bike or elliptical machine will be all right.
Over dressing is pretty simple. Just put on lots of extra clothing and then go running. In doors is going to be the best, but out doors will work if you don’t have another option. This isn’t an ideal way to prepare but it is better than nothing.
Another, less effective, way is to do some high intensity exercise until your core body temperature is up to 100-101.5 and then go sit in the hot tub or a sauna.
Adapting to the heat takes about seven to fourteen days of heat exposure for one hundred minutes a day. You can do a much shorter period of three to five days and it will help you feel better when running in the heat, but for endurance events the longer period is what you should be doing.
The problem is that heat training makes you tired, so you don’t want to do this super close to your race date, but you have to balance that with not losing the heat adaptation you’ve tortured yourself to develop. Try to complete your heat training 3-4 days before your event.