Is Training in the Heat Good for You?

By Matt Fitzgerald • For Active.com

It's summertime and the weather is heating up. Soon you will be forced to take measures to avoid training in excessive heat, such as moving workouts from the middle of the day to the early morning or evening and transferring outdoor workouts indoors.

Not only is training in excessive heat uncomfortable, after all, but it also slows you down and thus doles out a smaller fitness benefit.

Or does it? Actually, new research suggests that training in the heat may be more beneficial for fitness than doing equivalent training in cooler weather. So instead of doing everything you can to avoid exercising in the heat this summer, you may want to use it (carefully) to your advantage.

The idea that suffering through a one-hour run or a two-hour bike ride on a 100-degree day could be more beneficial than doing the same workout in greater comfort and faster in 55 degrees may seem crazy. But there are other methods, including altitude training, that are known to enhance the effectiveness of exercise by making it more difficult. Heat training has the potential to boost fitness in a parallel way; however, like altitude training, heat training is not something you'd want to do all the time.

The proof of heat training's effectiveness comes mainly from research conducted by Santiago Lorenzo at the University of Oregon. In 2010 Lorenzo recruited 20 highly trained cyclists and had them complete a performance test in temperate conditions on two occasions separated by 10 days. Between the tests, all 20 cyclists completed a prescribed training program, but 12 of them did it in a controlled, hot environment (100 degrees) while the other eight performed their workouts in temperate conditions (55 degrees) matching those of the performance tests.

The 12 cyclists who underwent heat acclimatization improved their performance in the cool performance test by 6 percent. In addition, their VO2max and their power output at lactate threshold increased by 5 percent. There were no improvements among those who trained in a cool environment.

The authors of the study attributed the performance-boosting effects of heat training on endurance performance in cool conditions to improved efficiency in heat dissipation and increased blood volume. They also found evidence that it caused some changes in muscle cell enzymes, which may have contributed to the effect as well. Lorenzo and his colleagues are planning future studies to pinpoint the specific mechanisms underlying the performance benefits and to determine whether heat acclimatization enhances performance in a real-world temperate time trial.

In the meantime, you might wonder what the practical implications of these findings are for you. In this regard, it is important to note that it didn't take much heat training—just 10 days—to increase performance capacity in cool conditions. Therefore the results of this study do not suggest that endurance athletes should train in the heat all the time. In fact, that would be a bad idea, because no matter how heat-acclimatized you are, you can't go as fast in a hot environment as you can in a cool environment, and there's something to be said for going faster.

It is for this very reason that few elite endurance athletes train at high altitude all the time. Instead, they spend most of their time at sea level, where they can go faster, and then go to the mountains for brief "altitude camps" before racing.

So, one thing that this study might inspire you to do is to conduct your own "heat camp" before racing in temperate conditions. For example, instead of going out of your way to avoid hot weather, go ahead and expose yourself to it for the last 10 days of training prior to racing in a cooler place or at a cooler time of day (usually early morning).

Another viable option is to periodically expose yourself to hot weather in training over a longer period of time. While Santiago Lorenzo's study involved 10 consecutive days of training in high temperatures, it is likely that you could get a similar boost from doing one or two hot workouts per week for eight to 12 weeks. This approach might enable you to exploit the benefits of heat training not only when you race but within the training process itself.

If you decide to try either of these experiments, do it cautiously. For starters, don't exercise in temperatures above 90 degrees unless you are already in good shape. Aerobic fitness enhances heat-training capacity just as heat training enhances aerobic fitness. No matter how fit you are, it's very important that you give yourself a chance to gently acclimatize to training in hot weather before you attempt any kind of challenging workout in the heat. You can do this both by doing shorter, slower workouts in very high temperatures (90 to 100 degrees) and by doing normal workouts in progressively warmer temperatures (75, then 80, then 85, etc). Avoid training in temperatures much higher than 100 degrees.

Obviously, you'll want to be sure to have plenty of fluid available throughout your hot workouts. Since heat increases both the sweat rate and thirst, plan to carry or have access to a significantly greater volume of fluid than you would need for a workout of equivalent length in cooler weather.

Be aware, however, that staying hydrated has a very limited capacity to keep the core body temperature from increasing. A much more effective way to stay cool is to slow down. Listen to your body when training in the heat and go as slowly as necessary to remain relatively comfortable. Exertional heat illness is relatively rare because the nervous system ensures that we feel lousy before we're in real danger; don't try to override this self-protective mechanism.

Finally, when preparing to train in very hot weather it's a good idea to plan routes that allow you to get indoors quickly if necessary. For example, you might do an eight-mile run comprising eight one-mile loops around your neighborhood. It's a little dull, maybe, but it's better to be bored and safe than entertained and at risk.