Managing your core temperature is the top priority and key to maximizing performance on a hot day and winning the war of attrition. If your core temperature rises too high, you're done for the day (best case) and may end up in the hospital with something much worse. Below are some tips for preparing for and racing in the heat.
1. Avoid dehydration. Dehydration interferes with thermoregulation and cardiovascular function so staying on top of your hydration plan is key for maximizing performance. Maintain your hydration levels per your sweat rate tests (see below), but make sure not to over-drink. Sip fluids every 10-15' vs gulping them. The maximum gastric emptying rate for the average athlete is usually 1.5 liters/hr (~50oz). If your fluid intake exceeds your emptying rate, then things generally get messy. Note: There's a lot of literature out there on dehydration and it's effects on performance. Historically, a ~2% dehydration rate was shown to produce significant performance declines. However, some new studies are showing otherwise, but the ones we've seen pertain to events lasting less than 2.5hrs. So, for long course events, play it safe and try to stay within the 2% margin.
Sweat Test Calculation
Note: Perform sweats tests regularly and in different temperature and humidity conditions. The
more data points you have, the better you’ll be able to adjust on race day.
2. Use the wind resistance on the bike to your advantage. Pour water on yourself throughout the ride to keep your core temperature in check. On a super hot day, grab an extra water bottle at the last aid station on the bike and pour it all over you with about 1 mile to go to T2. This will allow you to hit T2 with the lowest possible core temperature.
3. Be patient on the run. As your core temperature rises, more energy is channeled to thermoregulation than to forward propulsion. This is why everyone runs slower in the heat. Expect to run 60-90”/mile slower on a super hot day. Don't force a faster pace until you know you can make it to the finish line. If you feel yourself getting hot, then slow down and/or walk the aid stations.
4. Use a cooling towel on the run. Roll it up, wrap it around your neck and tuck it into the front of your kit. It may feel slightly bulky at first, but you'll soon forget about it when you see how well it works. Keep it cool by pouring water (or ice water) on it at every aid station. Your neck is a key "pulse point" on your body, where blood vessels are close to the surface - so cooling these areas will transfer cooling to the blood flowing near the surface.
5. Ice is your friend. Pour it down your top or pants as needed.
6. Wear sunscreen. Avoid getting sunburned as it interferes with sweat gland functions reducing your body’s ability to cool itself. However choose a lighter sunscreen - such as aerosol spray vs. heavy lotion - which blocks pores and increases heat retention.
7. Helmet selection can also play an important role in keeping your core temperature in check. Generally speaking, the more aero the helmet the more it will trap heat. On a hot day, it’s often better to lose a couple of watts in favor of a well ventilated helmet.
8. Acclimate. An often an overlooked aspect of race preparation, heat acclimation sessions are aimed at conditioning your body's ability to perform at a high level in the heat. If done properly and with enough lead time, they will product the following benefits:
The heat acclimations sessions also mitigate serious health risks when you are exposed to the heat such as muscle cramps, headaches, nausea, vomiting, dizziness, loss of motor control, hyperthermia, shortness of breath and overall general fatigue.
Heat training sessions can be effective in as little as 10 days but 3-4 weeks is an ideal lead time. In order to be effective you must elevate the body temperature to produce moderate to excessive sweating. The ideal indoor or outdoor conditions for these sessions are 90+ degrees with 30%+ humidity. If done indoors, you can simulate the high temps by wearing long tech shirts and avoid having any direct airflow on you to prevent evaporative cooling.
IMPORTANT: Heat training sessions are not supposed to be performed during quality intensity sessions. This will reduce the training benefit/quality of such key sessions. On a related note, the same principle applies to the timing of you key intensity sessions - you should avoid performing any key intensity sessions during the peak heat of the day. You'll have higher quality workouts if you do these intense workouts in the morning or inside with a fan.
You can also use steam and/or sauna sessions to obtain similar benefits. If you choose this approach, give yourself about 4 weeks to gradually and safely increase the duration of the sessions. Two sessions a week is generally adequate. Start off at 10’ and work your way up to 30-40’ over the 4 week period. Make sure to hydrate during these sessions.
About Meridian Performance
Meridian Performance (www.meridianperformance.com) is multisport coaching firm owned by USAT Coaches and veteran District Multisport members Jennifer and Darren Rentch. Since 2010, they have guided their athletes to peak performances including pro qualification, Kona, 70.3 Worlds, ITU Worlds, USAT Nats, State time trial championships, Ultra podiums and Boston.
Jennifer is a 9x Ironman, 2x IM 70.3 Worlds qualifier, 3x AWA and USAT All American.
Darren is a 11x Ironman, 4x Kona qualifier, 3x 70.3 Worlds qualifier, 7x USAT All American and a VTS/MTS Series Champion.
They can be reached at firstname.lastname@example.org and email@example.com.