WHY OLDER CYCLISTS SUFFER FROM HEAT STRESS & HOW TO AVOID IT

By Chris Carmichael

Maintaining body temperature within a narrow range (97-99 degrees Fahrenheit) is not an easy feat for humans, particularly when you consider all the things that can push body temperature up or down, including air temperature, humidity, clothing layers, medications, dehydration, body size, and exertion. We also have to add age to the equation, because our response to heat stress changes throughout our lifespan. For athletes in the 50-70 year range, here are some things to keep in mind when training in the heat.

How Age Affects Heat Loss

Babies, children, and the elderly are at greater risk for heat-related illnesses compared to young and middle-aged adults. In the early years, babies and children have less skin surface area available for evaporative cooling (sweating), so in hot environments they can store a lot of heat and struggle to get rid of it. In addition, children – especially very young children – often lack the ability, autonomy, or understanding to move out of a hot environment, remove clothing layers, or reduce activity level.

On the other end of the spectrum, the elderly can also be at greater risk for heat illness due to a lack of mobility, but even physically active older adults suffer more than younger adults in the heat. In response to passive exposure to a hot environment (not exercising) for 3 hours, a 2016 study showed that both younger (19-28yrs) and older (55-73yrs) groups responded similarly in the first hour, but that the older group stored more heat (heat loss decreased) as time went on. They cited reduced blood perfusion to the limbs as a potential limiting factor for evaporative cooling in the older group.

Reduced sweat response in older athletes was also observed in another 2016 study that examined sympathetic nervous system activity in response to heat. They found that older adults (67yrs) had a reduced vasodilation reflex in the skin compared to younger adults (23yrs), meaning both groups responded to heat exposure by dilating blood vessels in the skin, but that reflex was blunted in aged skin.

Chris Carmichael leading a ride through the Southern California heat

How Fitness Affects Heat Loss

I’ve previously written about the fact people start sweating earlier, more profusely, and from more areas of their skin as a response to increased fitness. This is one of the key adaptations to being more active. As you increase the amount of work – and therefore the amount of heat – you can generate in a given time, your body ramps up its cooling mechanisms to be ready for the demand.

Body mass also plays a role in heat loss. Both overweight non-athletes and athletes store more heat compared to smaller individuals. This has been researched by militaries, as they try to adapt training methods for larger recruits. Cooling a larger body also puts more strain on the cardiovascular system because there are more blood vessels perfusing more skin surface area.

Older Athletes are More Vulnerable to Heat Storage

In older athletes, fitness improves “sweat efficiency” compared to sedentary older people, but not to the same extent as it does for younger athletes. So, similar to the way VO2 max gradually declines through the decades after 40, your fitness-related adaptation to sweat response diminishes as well.

A 2015 study looked at younger (27yrs) and older (57yrs) firefighters, as well as non-firefighters of similar age (53yrs) and concluded that both the older groups stored more heat during intermittent exercise compared to the younger group, but the older non-firefighters stored significantly more heat than the older figherfighters.

Similarly, another 2015 study of female athletes showed the older group (58yrs) dissipated less heat through sweating compared to the younger group (23yrs). In this study, the subjects were matched for skin surface area and fitness level (VO2 max), which wasn’t the case for the firefighter study. Interestingly, as exercise workload – and therefore heat generated – increased, the differences between the groups’ responses grew.

Heat-related Advice for Older Athletes

If you are over 50 and feel like you’re less tolerant than you used to be of moderate- to high-intensity exercise on hot days, you’re probably right. There is a lot of personal variability involved, too, meaning heat tolerance or performance in heat changes differently for different athletes. Nevertheless, here’s what athletes over 50 should do:

Stay on top of hydration status

Dehydration hurts performance for everyone, but for older athletes who are likely to store more heat and have a diminished sweat response, staying hydrated becomes even more important.

Check your medications

Some medications can affect your ability to deal with heat. Beta blockers, for instance, slow a person’s heart rate, which can make it harder for the circulatory system to move heat to the skin. Some antihistamines and antidepressants can hinder sweating. Consult your physician to review your medications and see whether they may affect your heat or sun sensitivity.

Lose weight (if applicable)

If you are overweight and fit – as many cyclists over 50 are – losing some weight can help improve your heat tolerance. First of all, you won’t have to work as hard to maintain a given pace – particularly uphill. You’ll also have less insulation to keep the heat in, and greater “sweat efficiency” to move the heat out.

Be more heat conscious

Most of the habits and behaviors that work for younger adults are also essential for older adults, but it is important for athletes over 50 to recognize they are more vulnerable to heat stress and need to be more conscious of their habits in the heat. Exercising at cooler parts of the day, wearing summer-weight apparel, and dousing the head and body with water are all good recommendations for athletes of all ages. Here are four articles related to the science of exercise and performance in the heat: