Heat Acclimation

Dealing with the heat, at least initially, is always an issue. I think it is fair to say that most if not all endurance athletes have experienced some degree of cramps at one time or another, and most likely while racing or training on a hot humid day. Even those who live in hot climates need to acclimate somewhat to the hotter conditions of the mid-summer months of June, July and August, especially if you plan to race during that time.

When it is hot, especially when temps are in the 90-100F (36-40C) range, your body needs to work harder to keep your core temperatures in a safe range to allow the organs to function normally.

Jason Betz

One of the ways your body keeps cool is by circulating blood to the skin. This allows the internal heat building inside to be transferred to the environment. Core temperatures of 104F (40C) have been observed with marathon athletes. So, transferring heat to the outside plays an important role in helping your core keep cool.

One of the issues with more blood circulating to the skin while exercising, especially when you are not yet acclimated to hotter temperatures, is that you only have a fixed amount of blood to be circulated among the skin, internal organs and the working muscles. This results in less blood volume centrally surrounding the heart. If there is less blood flowing into the heart, there is less blood flowing out of the heart. So that means the heart needs to pump faster to keep up with the demand to keep cool, operate organs, and keep the muscles working.

Less fluid flowing around internally will cause a drop in blood pressure. The drop in blood pressure leads to constricted blood vessels within the internal organs, which in turn restricts blood from flowing to the skin and muscles, where it is needed for energy and cooling purposes. This results in a faster increase in core temperatures.

While sweat rates are usually not affected by all of these adjustments made by the body, the cooling effects of sweat alone are not great enough to keep the core temperatures cool. Also, the rate of sweat evaporation, which creates the cooling effect, is determined by the environment. So if it is humid, your sweat will remain on the skin a lot longer.

While not acclimated to the hotter temperatures, your body will do everything possible to keep your internal organs working and if that means taking blood away from the working muscles, then that’s what will happen. Less blood flowing to the muscles will not allow you to work at your full potential. You will go slower than normal, and most likely will experience cramps from dehydration due to the reduced amount of fluid flowing into the muscles.

Fortunately for all of us, our bodies adapt. It takes time for the body to make changes but it does happen. One major change is an increase in blood plasma, creating more blood volume. This prevents a greater loss in blood pressure while it is hot, which keeps the pathways open for blood flow to the skin, internal organs and working muscles. However, these adaptations are only evident when consistent exercise in the heat is performed. And when working harder, more progressive efforts, these adaptations can be sustained for up to three weeks. So if you are only exercising once in a while and spending a lot of time in air conditioned rooms, acclimating to the heat will not be as effective.

While it is good to adapt to the heat during the hot summer months, it is also good to limit the amount of training done in the hotter temperatures. You produce less power while working in very hot temperatures, even while acclimated. That will lead to fewer potential gains and more stress on the body. Too much training in the heat can actually have a reverse effect and result in a loss of fitness.

Adapt to the heat by living in the heat, race in the heat to allow for progressive efforts to be performed, but keep most of your quality training when the temps are cooler. Once you begin to acclimate, training in temperatures 10-20 degrees cooler will allow you to retain more blood flow within the working muscles, which will allow you to produce more power and make more gains.

Adapting is a natural process and one that most will deal with at some point. The advantage of living in a hot climate is that it gets hot sooner than it does in the northern climates, allowing for better preparation for the early season races in 90-95F temperatures (32-33C). But there will still need to be a process to adapt to the 95-100F (37-38C) temperatures of mid summer. So it is best to realize that heat adaptation is necessary and a process for all but pushing the limits training in the heat too often is not the best practice.

Race hot and train cool!

Mike Schultz CSCS


1 – Taylor N, Cotter J. (2006). Heat Adaptation: Guidelines for the optimization of Human performance. International SportMed Journal, Vol 7 No. 1, 33-57.

One response

  1. Pingback: Can You Take the Heat? Heat Acclimation Tips for Cycling in the Summer Months |

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