Decreased Athletic Performance in Hot Environments

It is commonly believed that reduced athletic performance in hot environments is due to an increase in the core temperature of the athlete. In this post, we are going to look at some research that may hint to a different cause.

In this study, ten male cyclists performed two 20k time trials, one in a HOT trial of 95 degrees Fahrenheit and the other in a COOL trial at 59 degrees Fahrenheit. Rectal temperature, core temperature, power output, and the integrated electromyographic (iEMG) activity (aka efficiency of the electrical activity) of the quadriceps muscles were all recorded throughout the exercise.

As to be expected, power output and iEMG of the participants began to decrease much sooner when the time trial took place in the hot environment. However, what is very interesting is that during the HOT trial, body temperatures, heart rates, and perceived exertion at the time of these decreases were all similar to that of the COOL trials, except it occurred sooner.

Also of interest is that during the both the COOL and HOT trials, the core temperature of the body at the time of decreased power and iEMG activity were similar. This suggests that decreases in athletic performance in the heat are not due to increased core temperature, because it never actually increased to a greater degree than in the COOL trials. The researchers concluded that performance decreases occurred before actual abnormal increases in body temperature. This is likely an anticipatory response by the brain to prevent those body temperature increases from happening in the first place, disrupting homeostasis, and potentially causing system failure.

In short, the brain is anticipating what is to come, and inducing fatigue to prevent damage to the body.

What can we learn from this study? It is that, when the protective mechanisms of the body are functioning properly, the brain will slow down the athlete before any damage actually occurs. All of this in an attempt to keep the temperature of the body from increasing to a dangerous level.

What do you think about this research showing it may not be your core temperature that slows you down in the heat?

In a future post, we will look at methods of keeping the body cool during training and racing!


Tucker, Ross, Laurie Rauch, Yolande Harley, and Timothy Noakes. “Impaired exercise performance in the heat is associated with an anticipatory reduction in skeletal muscle recruitment.” PFLÜGERS ARCHIV EUROPEAN JOURNAL OF PHYSIOLOGY. 448.4 (2004): 422-430. Web. 16 Sep. 2012. <>.