Indoor and outdoor environmental physiology plays a large role in athletic performance. Excess thermal energy, and it’s removal from the body, is what we will be dealing with in this post. The human body is an amazing thing, however approximately 75% of the energy produced by metabolizing glycogen, fat and amino acids becomes thermal energy. There is some variation in this depending on the sport and the athlete. A slight increase in body temperature is actually desirable, as metabolic reactions occur faster with a raised body temperature.
Normal core temperature is 37°C (98.6°F). During intense exercise in the heat, this can elevate to 40°C (104°F). Much above 41°C(105.8°F), proteins within the body will begin to denature. This is not a good thing, and the central governor system will start putting a clamp on the number of muscle motor units that can be recruited before this point, at least in most people.
Even when training indoors, we need to pursue proper cooling. The room I train in is approximetely 55-58 degrees in the winter. I performed an experiment using a different number of fans, and introducing even cooler air by opening a window. The workouts were the same, performed about 2 weeks apart from each other. The workout I used is termed the Stacker; the athletes I coach are quite familiar with this workout, as it comes up a lot over the winter months. All of the intervals are performed at to just above threshold. There are 40 minutes of total work at threshold, with the work intervals becoming shorter and the rest intervals becoming longer as the workout progresses.
In this first workout, I road with a fan on low for the warm up and first two intervals. I then turned two fans on high for the remaining two intervals. With the two fans on high, there was a notable downshift in heart rate of 4-7 bpm, while at the same wattage. I also noted my respiratory rate was slightly lower, as was my perceived exertion. All the work intervals were at an average power of 300 watts +/- 2 watts.
In this second workout, I road the entire time with two fans on high, and then opened a window right before the intervals were going to begin. My heart rate was nearly 10 bpm lower than the previous experimental ride, and yet my wattage was 15-20 watts higher. I was able to target 320 watts on all the work intervals. Some of this upshift in wattage can be contributed to added fitness of the 2 weeks of training. However, the heart rate response can not. Heart rate is largely a response to the total stress being put on the body. All of the stress factors external to training were pretty similar for both workouts. I had much better thermal cooling during the second workout, meaning my body could use more resources to produce power and fewer to cool itself. There was likely less of a clamping effect from the central governor as well during this second workout.
Training and fitness is an input/output equation of sorts. You apply a training stress to the body, this produces a positive adaptive response. This second workout allowed me to perform better during the work intervals, recruiting more motor units. It will produce a better training response. The body dissipates excess heat via radiation, conduction, convection and evaporation, with the vast majority via convection and evaporation. Even when training indoors in a cool room, you will build a layer of warm air around you. Having air movement will dramatically increase the effectiveness of both convective and evaporative cooling.
Train smart, and stay cool!