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.
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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.
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