Contributed by Dr. Steven T. Devor – Director of Performance Physiology for MIT and OhioHealth, and Associate Professor of Exercise Physiology, Department of Human Sciences, and Department of Physiology and Cell Biology, The Ohio State University
Many runners do not enjoy running on treadmills, even when the winter months arrive and the outdoor temperatures become very cold. However, running outside in the very cold weather presents a unique set of physiological challenges. And, from a practical perspective running outside in the winter also requires care to be taken to prevent injury related to falls on the ice or snow, and from frostbite due to exposed skin.
I have written before about the unwarranted fear of breathing in cold air when exercising outside during the winter months and that article can be found here. I would encourage everyone to read through that article again to understand exactly what happens to the air you breath in when outside during the cold winter temperatures. Two summary points from that article. First, the cold air that enters your mouth and nose when you inhale never reaches your lungs. By the time the inhaled air is in the lower part of your trachea it is warmed to body temperature (98.6 degrees Fahrenheit) and is 100% humidified. Second, remaining hydrated is still very important even in extremely cold temperatures.
Running in the cold also presents challenges to those that are trying to closely follow their heart rate training zones. Simply put, compared with running in mild temperatures, running in very cold temperatures makes your heart work harder (increases the number of beats per minute) at the same exercise intensity. The difficult part is that the variance you may see in your heart rate is not predictable, and changes with the temperatures. The increase in heart rate during the cold temperature is also dependent on your clothing, fitness level, and your percent body fat.
If you are dressed appropriately for exercise outside in the winter, with moisture wicking layers and with your head and hands covered, your heart rate will be less variable in the cold temperatures. Additionally, the more aerobically fit you are the less variability individuals generally see in their heart rates. Finally, your percent body fat plays a significant role in your cold temperature heart rate variability. Individuals with higher levels of body fat simply have increased insulation, and their heart rate does not need to increase as much in an effort to keep them warm. The opposite is true for those that are lean during the cold winter months. Runners with a low percent body fat have to work harder to stay warm, and accordingly their heart rates will increase to a greater degree.