Posts Tagged Riding in the heat

What’s So Cool About being Hot?



Part  3

This article is ESPECIALLY for all of you hard core, tough and resilient cyclists who proudly proclaim “THE HEAT DOESN’T BOTHER ME.”  We just want to make the case that it’s a different statement than “THE HEAT DOESN’T EFFECT ME.”

Interesting – fascinating FACT. Did you know that depending on your size you have between 60,000-80,000 MILES of blood vessels in your body? And your body has an incredible ability to open and close all those vessels depending on a number of “things” it senses locally and systemically.

The term CARDIOVASCULAR refers generally to the heart as the pump and this astounding number of large and microscopic system of blood vessels that delivers everything every cell needs to survive.

For the sake of brevity we’ll consider some basic aspects of CARDIOVASCULAR changes that occur and place significant demands on the heart as well as other systems when cycling in the heat.

At rest and in a cool comfortable temperature your body circulates about 250-500 milliliters of blood to the peripheral circulation and only 20-25 % of your capillary blood vessels are “open”. What happens when you’re pushing the pedals hard in hot weather is astounding. First of all nearly 100% of those 80,000 miles of blood vessels are wide open and the heart is pumping 15-20 times as much blood per minute as it was at rest.

You don’t have to be exercising at all to experience a change in cardiac output in the heat. Even at rest your heart rate goes up a few to several beats a minute to accommodate stable blood pressure as more capillaries dilate in order to shed heat and keep you cooler.

The problem your heart has while riding in the heat is directing all this additional blood flow to two very important parts of your body – your working muscles and to the peripheral circulation so core temp doesn’t rise too fast. Not enough blood to your skin and you’ll over heat very quickly. Not enough to your working muscles and fatigue, cramping, lactate build up and bonking happens pretty fast. In some cases of extreme exercise in the heat 60 % of the cardiac output is directed to the peripheral circulation to facilitate evaporative cooling. That is a huge loss of blood flow to the demands of your working muscles.

The importance of skin temperature cannot be overemphasized. While it’s true that CORE temperature sets a ceiling on the duration of exercise [most mammals simply stop working when core temps hit 104 F.] pacing, endurance, power output and even neural-muscular impulses are driven more by skin temperature. The reason begins first because our skin is our “first responder” in regards to “sensing” the environmental conditions we will be exercising in. Ever walk out from a cool room into the heat to ride and immediately start “recalculating” the distance and pace you had in mind when it was cool inside? That’s because as soon as your skin feels the heat it’s sending messages to the brain – “NOT SO FAST and NOT SO FAR” today. I’d like to live to see tomorrow.

One of the most significant benefits of heat acclimation is a great capacity to sweat and to begin sweating earlier when exercising in high temperatures. The key advantage is the ability to maintain a lower skin temperature sooner thus lowering the amount of blood flow to the skin. Net benefit more blood to the working muscles and other organ systems which we’ll discuss in a later post.

Remembering the foundational principle of thermoregulation from a previous post, “The harder your body works to cool itself, the faster you fatigue” it becomes clearer why acclimation helps your body stay cool more efficiently.

It’s exactly this principle behind Spruzza as “A Cooler Way to Ride.” Not only does the application of 3-5 mL of water facilitate skin cooling but it’s using an external source of water [not your own sweat] to accomplish this. This is a key reason why in our field study we documented a lower level of dehydration when using Spruzza to stay cooler.

Another key observation and effect of spraying 3-5 mL of water over your face is that normally your sweat rate is only sufficient enough to drop your skin temp by about 5-8 degrees below core temperature but adding additional, external water increases the evaporative cooling capacity such that your skin temp will drop 10-20 degrees below core temperature. The result in not only amazingly refreshing it increases the rate of heat exchange by a factor of two to four fold.

The important conclusion in all this is that even if “the heat doesn’t bother you” it does have a physiological effect on performance, endurance, dehydration and recovery. Several major organ systems are effected as we will look into in later posts.

So no matter how tough you are, think about riding SMART, lowering the work your body does to cool itself. You’ll feel better, ride stronger and recovery faster. Who doesn’t want that?

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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



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.


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.


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.



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