In a word, NO! For a more in depth answer, one of my coaches, Renee Eastman recently answered the exact same question for one of her athletes. Her answer was exactly what I would have written, so Ive pasted it below:
Remember that the goal of training is to make the body adapt to the workload youre placing on it. Restricting water intake does not cause any positive training adaptation. Similarly, passive heat exposure like you'd get from just sitting in a sauna, has not been shown to be as effective as exercising in the heat to elicit practical heat acclimation for improved performance in hot conditions.
Adaptations to heat exposure while training include an increased sweat rate and a lower body temperature to induce sweating. Another adaptation related to heat exposure is increased plasma volume, which also results in a lower heart rate in the heat (versus non-acclimated). These adaptations improve the body's ability to disperse excess heat, but it takes extended exposure over repeated days to get the adaptation process started. By extende,d I mean exercising for at least one hour at a time. There will be some adaptations seen within the first three to five days, but with the general recommendation for better acclimation after ten days.
When trying to heat acclimate there has to be a balance between safety and maintaining training quality. When first starting heat acclimation you want to be careful not to overdo and you may need to reduce volume and intensity during the first few sessions. Also to note, initially you won't be able to exercise as hard in the heat, so when choosing the appropriate workouts, you want to avoid those workouts that need maximum effort for the best benefit. This is especially true when preparing for a big event. You need to balance the need to acclimate with the need to get in the best quality workouts. Also, as you are heat acclimating, realize that intense or extremely long workouts will take a higher toll on your body, so you want to be careful as you approach the days before your big event. In the final two days before your event, you want to avoid prolonged or intense heat exposure as the resulting fatigue would be worse for your performance than any workout you performed at that point.
There is of course a lot of personal experimentation that goes into heat acclimation. Some do better in the heat than others, just naturally. If you do have events that are in hot or humid climates, its to your advantage to expose yourself to those conditions while training. If you cant replicate the hot conditions in training, you may need to take more drastic cooling measures when training or competing in the heat, like pouring water over your body as well drinking water and sports drinks.
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