bike75.gif (2872 bytes)


  Last updated: 12/06/2009

Handling Heat
Hyperthermia - Hypothermia

Although hyperthermia is often the first thing thought when discussing heat issues with cycling, hypothermia is the other end of the spectrum of what I will call "heat illnesses". The "heat" equation for an individual at any point in time is the sum of heat production from their metabolism and the heat gained/lossed from their environment. Heat energy is a byproduct of your metabolism. Conversion of ATP to ADP is inefficient with 70% of stored energy released as heat. During exercise heat production is increased approximately 20 times your basal level.


Heat stress during exercise may cause sudden death as late as the next day. In military recruits there is an increase in exercise related deaths the morning after intense exercise before the temperature rises. Heat, humidity, and direct sunlight seem to correlate with the problem so be careful to stay hydrated and wear the correct clothing.


Heat gain/loss from your surroundings is dependent on the ambient temperature. As problems during exercise are usually related to shedding excess heat produced, let's focus on the ways your body can eliminate excess heat energy to maintain a temperature in a normal range. Heat "unloading" is dependent on

Sweating is the only effective way to cool your body if the ambient temperature is >92 degrees fahrenheit. And as it requires evaporation, it's effectiveness drops off quickly at >90% humidity. You have anywhere from 2 to 4 million sweat glands and can sweat up to 2 to 4 liters per hour. In fact Alberto Salazaar was estimated to lose 1 pint every 11 minutes in the 1984 Olympics. The heat energy loss from sweating is in the neighborhood of 580 Calories per hour.

When there is an imbalance of heat production > heat loss, hyperthermia occurs. Muscle cramps may be the first sign of hyperthermia. Next in the spectrum of heat exhaustion is the stage where you are hot, fatigued, nauseated, but still sweating. And finally there is heat stroke where you stop sweating, your core temperature begins to rise (often >104 F), and nervous system symptoms (altered state of consciousness or confusion) appear. It is potentially life threatening.

Another aspect of heat injury is hyponatremia. When you lose sodium in sweat (15 - 50, avg 20 meq per liter, depending on sweat rate and acclimitization) and replace it with pure water, your serum sodium concentration can drop below normal (hyponatremia) with serious consequences. Recent studies have shown that there are "salt losers", those with the salt crusted on their jerseys after an event, that may need even more than the normal salt replacement. It is thought that these athletes may carry the single gene for cyctic fibrosis (present in 5% of caucasians).

How do you protect yourself from hyperthermia? There are really just a few things you can do:


Hypothermia is a decrease in your core body temperature. It is always a risk for the cyclist, especially in that combination of conditions that often occur with winter training.

What are the warning signs?

ADDITIONAL ENERGY REQUIREMENTS - (at rest) in a cold environment

Questions on content or suggestions to improve this page are appreciated.

Cycling Performance Tips
Home | Table of Contents | Local Services/Information