WHAT’S SO COOL ABOUT BEING HOT
What’s so cool about being hot? Turns out NOT MUCH. In fact studies have shown that without an ability to get rid of heat, the longest time you could exercise is about twenty minutes.
Overheating effects just about everything when you’re exercising. While cyclists have a significant advantage in terms of cooling down because of the wind speeds we generate there remain several challenges to thermoregulation on the bike especially when temperatures are over 85-90 degrees F. Another study demonstrated that the optimal temperature for cycling performance is about 68 degrees F. The farther you get away from 68 in terms of heat the greater the demands placed on your body to respond and get rid of the heat you’re generating.
The most fundamental physiological principle involved with exercise and overheating is this, “The harder your body works to cool itself the faster you fatigue”
This post will explore the first of several reasons this statement is true.
For simplicity sakes we’ll break down this topic on heat and physiology into five broad categories
- HOMEOSTASIS AND THERMOREGULATION
- MENTAL – PSYCHOLOGICAL, PERCEPTUAL AND COGNITIVE FUNCTIONS
- STRESS AND ADAPTATIONS
HOMEOSTATIS AND THERMOREGULATION
Human bodies are incredible machines. While most of us look in the mirror and can pick out all kinds of “imperfections” we really are to quote the Psalmist, “fearfully and wonderfully made.”
Scientists from a variety of disciplines are on a regular basis discovering more amazing and intricate systems that allow us to survive, adapt to an increasing number of environmental challenges, and maintain a very tightly balanced, integrated system that keeps us well, safe and comfortable.
When we hop on our bikes and begin generating power to the pedals in hot weather – our mechanisms of homeostasis can get stressed to the max. These homeostatic processes when the subject is heat are called THERMOREGULATION processes.
As noted above, without the ability to dissipate heat the human body would lose the capacity for work in about twenty minutes. Obviously we are capable of much, much more. That’s possible largely because we have several built in and environmental capacities to get rid of all the heat we generate in the process of muscular activity.
Your body has five distinct, somewhat related and integrated systems for eliminating heat generated whether at rest or during intense physical activity. Each mechanism utilizes certain principles of physics and interaction with the environment you happen to be in at the time.
Here they are: RADIATION, CONVECTION, CONDUCTION, EVAPORATION and RESPIRATION.
We are going to consider more closely CONDUCTION and EVAPORATION because they play the MOST significant roles in heat transfer when it’s hot.
We get rid of heat by RADIATION essentially when we’re standing still and the environmental temperature is lower than our body temperature. Heat always flows from HOT to COLD. This is not only pretty simple, it’s also not the condition we’re talking about because we’re on our bikes moving very fast and in temperatures above body temperature.
CONVECTION is related to RADIATION because it involves heat radiating away from the body by moving air over the surface – in this case our skin. This is why even standing still with minimal sweating we feel cooler when a fan is turned on and blows a nice breeze over us. True CONVECTION obviously plays a role when we’re moving on our bikes but again it fails to benefit us when the temperature is significantly above our body or skin temperatures.
CONDUCTION is the transfer of heat – again from HOT to COLD by direct contact between surfaces and materials. Conduction is THE main and initial mechanism of heat transfer from our CORE [be that intestinal, cerebral or working muscles] to the PERIPHERY our outer layers – DERMIS and EPIDERMIS. As blood is HEATED up traveling through your CORE tissues it is pumped to the PERIPHERAL circulatory beds taking the heat out of the CORE and to the skin where it can be dissipated by RADIATION, CONVENCTION, CONDUCTION and EVAPORATION. Again, the environmental conditions will determine which method of heat loss – transfer works and by how much once the HOT blood gets to the skin.
EVAPORATION is the tremendous cooling effect and the only cooling mechanism that works once the environmental temperatures are above or well above your skin temperature. Technically it’s called the “latent heat of vaporization”.
When water as a liquid goes to a gas phase – evaporates – heat is lost in the energy transfer. This leaves the surface – your skin in this case – cooler in the process. The water that is evaporating is of course YOUR SWEAT.
SYSTEM INTEGRATION – CONDUCTION-EVAPORATION-CONVECTION form a critical systemic process that makes heat dissipation possible when you’re exercising in hot conditions. The “super-heated” blood from your core is CONDUCTED by blood flow away from the core to your skin. Without EVAPORATION your skin would just HEAT up making CONVECTION and RADIATION useless heat-loss mechanism because the air temp is HIGHER than skin temp and of course CONDUCTION from the blood would fail to for the same reason – there is no temperature drop between the blood and the skin.
Because EVAPORATION lowers the skin temperature the HEAT in the blood can be conducted from the blood into the skin and then lost to the environment.
ALL SKIN IS NOT THE SAME
The average surface area for men and women are 1.9 and 1.6 m2 respectively. The total skin surface area represents the platform from which heat can be exchanged. For our purposes we are concerned about the surface area available for convection, conductive and evaporative cooling.
It is also very important to know that not all of the skin surface area is the same in regards to the ability to conduct heat away from the CORE and then by EVAPORATION to the environment. The skin over the palms of the hands, the soles of the feet and of course your face, neck and ears are especially effective at dissipating heat. These specific non-hairy areas of the body not only are less insulated by hair and fatty layers but they have dense vascular-capillary beds where heated blood can flow conducting heat away from the core. With the exception of your ears your head, hands and feet also have a significant number of sweat glands.
We’ve all enjoyed dipping our hands and feet into a cool pool, stream or lake while taking a break on a hot ride but on the bike our feet are in shoes and our hands are usually in gloves so that leaves our head, face, neck and ears as the most accessible and safe way to cool down.
And so that’s what we do on the bike we dump water over our heads because it’s one of the most efficient parts of our body for getting rid of heat – cooling down – and it’s the most accessible while riding. The only problem with dumping water from your bottle is that while you’re cooling an effective part of your body you’re using an ineffective means of doing so. You still need a more efficient cooler way to ride. Remember it’s only the water that sticks to your skin that gives you the evaporative cooling effect. When you’re dumping water from your bottle most of it just falls off and hits the ground wasting what you could or should be drinking.
Common sense and science come together rather nicely.
In summary when you’re cycling in hot weather you MUST have solutions for HYDRATION, FUELING and COOLING.
In a recent conversation with cycling coach, Chris Carmichael he stated, “Thermoregulation is the next big thing.”
We couldn’t agree more.