Heat & Humidity
Having a better understanding of how our bodies react to extreme heat, understanding how to optimize training in the heat, and knowing heat-illness warning signs will allow us to take an intelligent approach to our training during the Texas heat. You may have heard me say, “there is a fine line between tough and stupid”, and for heat illnesses it is especially true. In no way do I want you to shy away from pushing yourself, but you need to be in tune with your body.
Your Body’s Reaction to Training in Hot/Humid Temperature
Our body is amazing and has a built-in thermostat (Hypothalamus) that controls the body’s responses to heat. The primary mechanisms that cool our body are convection (wind), conduction (physical touch), radiation, and evaporation. In essence, our body is continually regulating temperature based on environmental and internal conditions.
The most important of these measures during exercise is evaporation of sweat from our skin. Under dry conditions, this mechanism can effectively cool our body but in the muggy conditions of Austin, our body has a tougher time cooling. The reason is the humidity; if water vapor is saturating the air around us, we cannot effectively evaporate sweat off our skin.
Under these conditions, both our skin and core temperature rise creating a physiological competition between working tissues and our skin. As the core temperature rises blood is distributed to the skin for cooling, but as exercise increases in intensity, your muscle will win out and prevent the blood from being directed to the skin. This competition is especially exasperated when dehydrated. (Coyle and Montain, 1992; Gonzalez-Alonso et al., 1995)
Dehydration is especially detrimental to CrossFitters because we are constantly trying to stave off “metabolic stress”! So here is food for thought: if you wake up in the morning after a hard workout and you weigh 5 lbs less than the day before, it’s not a miracle… it’s dehydration. “For every 1% of body weight lost due to dehydration, your heart rate will increase 5-8 beats per minute.”, so good luck staving off that distress.(Brown, 1947; Coyle and Montain, 1992a,b; Sawka and Coyle, 1999; Cheuvront, 2001; Cheuvront and Haymes, 2001; Sawka et al., 2001)
The great thing about our body is it can adapt to these conditions. Now we could take the unscientific approach and “suck it up” or we can be smart and ensure we are ready for the heat. I have participated in military operations in the Mojave Desert, Iraq, and Afghanistan, but the humid conditions of the Southern United States are by far the worst I have experienced.