On Sunday I returned from two weeks in Italy. The first week was a vacation and in the second I put on a training camp in Riccione on the Adriatic coast. During the first week temperatures were in the 80- to 90-degree Fahrenheit range (26-32C). Then it cooled off for the camp after a storm moved through the region with temperatures in the 50F to 70F range (10-20C). I arrived home back in Scottsdale, Ariz. on Sunday evening and the next morning started a three-hour ride at about 10 a.m. Big mistake. It was about 90F (32C) at the start and when I got done it was around 100F (38C). It peaked out at 105F that day.
The planned workout called for some long hill-climbing intervals at functional threshold power. The second big mistake. Besides being jet-lagged I was certainly not ready for such extreme temperatures. After a warm-up followed by the first interval it became readily apparent such a workout wasn’t a good idea. It was way too hot. So I rode steadily at a low intensity instead and made the workout about 20 minutes shorter. Even with that it became a challenge near the end just to maintain pace. The perceived effort steadily increased as evidenced by a rising heart rate despite steady power. In the last 90 minutes I decoupled 10% even with the low and steady power. “Decoupling” is just another way of saying that my heart rate drifted higher relative to power. It’s a method for comparing power on the bike (or pace in running) with heart rate over time to see how much they separate. A high rate of separation can be caused by several factors including heat.
Now is the time of year when you may also be experiencing hot workouts and races for the first time this season. While the highest temperatures where you live may not hover around 100F, even somewhat cooler conditions with high humidity may be too great in the spring for aggressive training and racing. And the greater your body mass, the greater the negative consequences of a hot environment. For example, a 200-pound (90kg) athlete will produce and retain more body heat than a 120-pounder (55kg).
The following are a few heat-coping strategies that have come out of research to consider when planning a high-intensity workout or doing a race in hot weather. I’ve listed them in what I consider to be their order of importance with the most effective strategy listed first. There is also a link provided to research supporting each should you want to read the abstract for the study.
#1. Acclimate. It takes about 10 to 14 days of frequent exposure to heat for your body to adapt. During this period of time workout daily in hot conditions at a lower-than-normal intensity. After a couple of weeks of near-daily exposure to hot conditions you will begin perform better in the heat than prior although performance will still likely be diminished from what you might have done in cooler conditions.
#2. Shorten the warm up. In hot conditions you will warm-up adequately with a shortened version of what you normally do and experience less stored body heat at the start of the race or higher-intensity workout portion.
#3. Stay cool prior. Several strategies have been used in studies, but few may be readily available to you. For example, soaking in cold water and wearing an ice vest immediately before exercise in the heat have been shown to improve performance. Drinking icy fluids may be of some benefit, also. But, of course, this benefit of pre-cooling is greatest in the early part of the race or workout and quickly diminishes as the session progresses.
#4 Stay cool during. There isn’t a lot of research available on this, but draping an ice-filled container around your neck while training or racing in the heat may improve endurance performance. Runners may even try putting ice from aid stations in their hats.
#5 Hydration. Your body fluid status may affect how well you perform in the heat, but, unfortunately, most of the research is poorly designed relative to what athletes actually do in hot environments. Be aware that over drinking is a far worse matter than dehydration. No one has died from dehydration in a race, but there have been several deaths due to over-hydration-caused hyponatremia. And even if you don't die, performance is likely to be decreased in the early stages of hyponatremia. The key here is to drink when thristy–not to a predetermined schedule.
Sodium intake doesn’t appear to have any benefits for adaptation to the heat (see a previous post on this topic here). But there are a couple of studies suggesting that you may need more carbs and protein before and after a hot workout and that the benefit of carbs taken in during exercise is reduced. The clothing you wear can also have a modest impact on performance in the heat.
Perhaps the most important matter is realizing you need to train or race more conservatively when it’s hot. For a planned intense workout keep the pace or power the same but shorten the work intervals and lengthen the recoveries (heart rate is not a good indicator of intensity when it's hot). You may need to do less total high-intensity work in such a session. In a steady-state race, such as in road running or time trialing, everyone else will start too fast and wither. Start slower than usual, be patient, and they will come back to you. Be aware that your heart rate will be higher than normal for any given sub-maximal pace or power. Don't let that concern you. It's just a part of exercising in hot weather.