I raced the Furnace Creek 508 through the Mojave Desert and Death Valley in 1989 and 1993. I set a course record and won both times. I raced for over 30 continuous hours in each of those two races.
The 508-mile race, with 35,000 feet of climbing, is a qualifier for the Race Across AMerica. I wasn’t the fastest rider—many would have beaten me in a 40-km time trial. I wasn’t the lightest rider, nor was I the best climber.
But I was the smartest about riding in the heat!
Here’s what I learned about racing in the heat, which I’ve “road tested” as a coach working with ordinary roadies over the years since.
Sources of Heat
Even in very hot conditions, most of the heat is generated by your body, which is only about 25% efficient. For every four calories you consume, only one calorie provides energy to move you forward—and the other three calories produce heat. That heat must be dissipated from your body, primarily through sweat.
Your body is like a car’s radiator. Blood circulates through your core, heats up and circulates to the skin, where heat is dissipated via sweat.
The more aerobically fit you are, the more prepared you are to ride in the heat. Endurance riding increases plasma volume so that your body can better transfer heat from your core.
Endurance riding increases your riding efficiency so that you ride with a lower heart rate under normal conditions. This means that when riding in the heat your heart rate can increase more to move blood faster through your “radiator.”
When you acclimate, you start to sweat at a lower core temperature, and you sweat more, which keeps your core temperature lower. Your total blood supply increases so that you can sweat more while still maintaining blood flow to the muscles. Thus, you disperse more heat both by convection (the increased blood flow to the skin) and by radiation.
You can bring about these changes through long endurance rides in hot conditions. You can also do specific heat adaptation sessions by riding hard enough to sweat heavily for 60 to 90 minutes.
If you are already very fit, you can achieve significant acclimatization by riding this hard on four successive days. If you aren’t quite as fit, you may need as many as eight sessions with a rest day in between each session.
You may be tempted to spend most of your time in an air-conditioned environment and just ride for a few hours at a time in the heat. However, you don’t acclimate fully unless you spend a lot of time in a hot environment; i.e. acclimate passively.
Again, about 75% of your energy makes you hotter rather than propelling you down the road. Even in relatively mild conditions you can overheat from internally generated heat!
Simple rule: If you start to feel too hot, slow down!
- In my Cycling in the Heat Bundle you can learn more about the science of riding in the heat, and managing your fluids and electrolytes. The cost-saving bundle of 2 eArticles is just $8.98 (a 10% savings) and, as always, just $7.64 for our Premium Members (includes their everyday 15% discount!).
- My Summer Riding Bundle includes the 2 Cycling in the Heat eArticles, plus Preventing and Treating Cramps, and Eating and Drinking Like the Pros. The cost-saving bundle of all 4 eArticles is just $15.96 (a $4 savings) and, as always, just $13.58 for our Premium Members (includes their everyday 15% discount!).
Ride by Effort, Not Pace
Riding when you are hot drives up your heart rate, so your heart rate monitor doesn’t provide useful information about how hard your muscles are working.
Because you can’t ride as hard when you are hot, gauge your effort by perceived exertion, not by your computer or HR monitor.
Because more blood flow is going to your skin to keep your brain, heart and other vital organs from overheating, less blood is available to your GI system to help transport food molecules to the rest of your body. The more you eat, the more blood flow is taken away from the process of cooling your body.
Fit Your Riding to the Conditions
Tailor your riding to the conditions at hand. In almost all conditions (humidity is one primary exception), mornings are a better choice than afternoons.
If you need to ride longer, then two hours of endurance riding in the morning and two in the evening will provide more training benefit than four hours mid-day, because you can ride more briskly when it’s not as hot.
Try to time your outings based on the forecast, if you have a choice. If possible, take your rest day on the hottest day of the week.
Moreover, in urban and suburban areas, the sun warms the pavement and other surfaces so that the heat grows throughout the day, often making late afternoons and early evenings nearly as hot as mid-day in these environments. Later in the day, ride in the countryside if you can.
Take Sun Seriously
Exposure to UV rays increases your risk of skin cancer. I’ve had three basal cell carcinomas removed.
Fortunately, this type of skin cancer rarely spreads and is easily cut out. However, I’ve had two friends die of melanoma.
When I was younger I thought that a cyclist’s tan lines were cool — not anymore! My dermatologist, whom I see twice a year, recommends sun protective clothing because it doesn’t sweat off like sunscreen. I wear UPF 50+ sun protective clothing. (Many companies these days offer a variety of such gear.) I wear either white arms and legs or a long-sleeve jersey. I use SPF 50 zinc oxide on any exposed skin.
Next week: I’ll continue on the summer riding theme with a look at hydration, dehydration and nature breaks.
If I may, I would like to make a few comments about a heart rate monitor’s usefulness in hot weather.
John Hughes’ advice about hot weather is excellent. However, his article suggests that heart rate monitors have limited usefulness in hot weather. In preface, it should be noted that I typically advocate device and technology independence; although, I also hold that position lightly.
My experience with heart rate monitors in hot conditions suggests that such devices can be especially valuable. Having used a heart rate monitor for a number of years, I generally know what my normal heart rate should be, for given workloads in given settings. In hot conditions, I have found it helpful, indeed important, to closely monitor my heart rate, and a heart rate monitor is particularly well-suited for this purpose. More specifically, I’ve located that when the temperature is hot, and the heart rate monitor shows my heart rate is higher than normal (for the conditions), it is a reliable indicator for the need to slow down, even if I’m feeling good, and keep my heart rate in its “normal” or perhaps “low normal” window. Without the heart rate monitor, it is difficult to closely monitor, just from “feel” when my heart rate is a little too high or trending up. I know from “feel” when my heart rate gets especially high, (or when I’m well over-heated), but then it’s also too late. Experience confirms that there is a repeatable correlation between close heart rate monitoring, appropriate response to the presented data, and outcomes.
It is important to note that there is a synergy between the rider’s real-time experience and the heart rate monitor, and that interpretation is necessary to arrive at useful results. Also, the approach presented here, depends on experience with equipment and one’s physiology, over time. To achieve the required experience, it may be necessary to reconsider the idea that heart rate monitors are not useful tools for bicycling in hot weather, and to actively use them in these settings. Experience suggests that a heart rate monitor is a helpful and valuable tool in hot weather, one that I have come to more fully appreciate by hard experience.
Thank you for your valuable efforts and guidance, they are genuinely appreciated.
All my best.
Wrong: I’ve located that when the temperature is hot
Should be: I’ve discovered that when the temperature is hot
Bernie Burton MD says
I highly recommend considering making all of your jerseys sun protective by using RIT Sungard once yearly on all of your outdoor shirts and jerseys. One rinse cycle with one box will give a 30 SPF for 25 washes. Two rinse cycles with 2 boxes will give a 50 SPF for 25 washes. It cost about $3.95 a box.