I was 46 when I bought my home in Boulder, CO in 1995 and the heating and cooling systems were like a cabin. When it was cold I chopped wood and built fires in the wood stoves. When it was hot I opened both low and high windows to increase the airflow. About 10 years ago my wife and I decided that getting up when it was only 50F in the house and building fires wasn’t tolerable any more so we put in heat in each room. This year we’ve decided that 85F in the house is too hot and we’re putting in air conditioning next week. As we age we feel less tolerant of the heat. But is loss of heat tolerance inevitable with aging?
Data collected across large samples of the older population show a correlation between age and hot weather and more heat-related illnesses and deaths. “Older individuals, regardless of how one classifies ‘old’, are the most rapidly growing portion of the population. Statistics from heat waves and other morbidity-mortality data strongly suggest that older persons are at greater risk of developing life-threatening manifestations of heat stress such as heat stroke.” Heat Tolerance, Thermoregulation and Ageing
However, the data are for the general population. It’s not clear the extent to which these heat-related problems are due to chronological aging or due to other factors. These variables change with may age and could affect heat tolerance independent of chronological age.
- Sedentary lifestyle. In the general population physical activity decreases with age. This contributes to the next five factors.
- Decreased aerobic capacity (VO2 max).
- Your body dissipates heat via two basic mechanisms: 1) greatly increasing blood flow to the skin and 2) producing and evaporating sweat. Decreased aerobic capacity means decreased blood flow and therefore less cooling.
- Physical changes such as decreased lean body mass and increased fat tissue. The basal metabolism slows by about 2% per year and this combined with less physical activity results in weight gain.
- Increased prevalence of chronic diseases. Decreased physical activity also increases the occurrence of hypertension, heart disease and diabetes.
- Increased use of prescription medicines. The chronic diseases are often treated with medications that reduce heat tolerance, e.g. diuretics, vasodilators, beta blockers.
- Chronic poor hydration from not drinking enough and/or increased fluid secretion by the kidneys.
If you keep exercising you can greatly reduce the effects of these factors.
Heat Dissipation During Exercise in Warm Conditions
Some physiological changes that affect heat tolerance are inevitable with age:
Decreased cardiac output. How much blood the heart pumps decreases by about 30% between the ages of 20 and 80. Cardiac output is a function of heart rate and stroke volume, how much blood your heart pumps per beat. While your maximum HR inevitably declines, through exercise you can maintain your ability to sustain a reasonably high HR and slow the decrease in the elasticity of your heart, which is what reduces stroke volume.
Decreased skin blood flow. Skin blood flow is 25-40% less in older athletes. The reduced flow is due to changes with the blood vessels in the skin. Staying very fit does not prevent the skin from aging.
Sweating rate. Compared to younger equivalently fit athletes, most older athletes have lower sweating rates. Although the same number of sweat glands are activated each gland produces less sweat. Genetics plays a large role in determining sweating rate and there is wide variability among older athletes. Decreased sweating is more of a problem in hot, dry environments than in humid ones.
The bottom line is good:
- As athletes get older the capacity to sweat declines although there are exceptions. This does not mean that older athletes are less tolerant of hot conditions.
- Older athletes can acclimate just as well as younger athletes.
- The ability to exercise in hot conditions is primarily a function of physical fitness, especially VO2 max, rather than chronological age.
- One caution is that the sensation of thirst diminishes with age. For athletes the general recommendation is to drink to satisfy thirst but not more because drinking too much fluid risks diluting the blood sodium to a dangerous, potentially fatal level. For older roadies be sure to drink enough whenever you are thirsty. For more information see my column 12 Hydration Myths.
Much of this information is from The Older Athlete: Exercise in Hot Environments.
My eBook Anti-Aging: 12 Ways You Can Slow the Aging Process includes information specifically for older cyclists on all of the different physiological changes with aging and how you can mitigate the changes. The 106-page eBook is available for $14.99.
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- Cycling in the Heat, Part 2: Hydration Management is 21 pages and covers how to determine how much you should drink depending on your physiology and sweat rate, how best to replace your fluids and electrolytes, the contents of different sports drinks, how to make your own electrolyte replacement drinks, how to rehydrate after a ride, and how to deal with hydration-related problems.
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