If you've ever struggled running in the heat, you are not alone. There are a few primary reasons why performance declines in warmer temps.
1) An increase in overall body temperature. Similar to a fever, the higher your core temperature, the greater the perceived effort (everything feels harder).
2) In the warmer temps, a significant amount of blood flow is redirected from the working muscles to the skin in order to cool the body. Cooling (which is very important to the health of your body - your organs don't want to overheat!) happens from sweating and evaporation. Therefore, less blood is available to transport oxygen to the working muscles. Less oxygen in the heat is similar to training at altitude. But in humid conditions, the air is full of water vapor and it can't hold any more so sweat has a difficult time evaporating (which means it can't cool you like it would be able to do in low humidity).
3) Dehydration increases in hot conditions. When you are dehydrated, you lose blood volume which causes your blood to get thicker. This makes it harder for your heart to supply blood to your muscles. As a result, your heart has to work even harder to pump that blood. Additionally, when fluid levels drop, you have a harder time controlling body temperature which causes the core temperature to rise even faster.
4) You DO NOT lose sodium without fluids. Dehydration comes from fluid loss - not from sodium loss. If you are simply focusing on sodium and carbs (salt tabs, gels and chews) but not drinking enough water each hour, the sodium and carbs will not do anything to help you avoid dehydration. You must drink enough of a well-formulated sport drink to properly keep yourself hydrated.
The bottom line is that the harder you work in the heat, the more heat is generated from the working muscles. Blood in your body competes for the working muscles (energy), the skin (to cool you) and the gut (aid in absorption and digestion of calories). The greater the metabolic heat production, the more energy is needed to cool the body (top priority to prevent you from overheating) - which means more stress on the cardiovascular system. Heat stress also causes an increase in fluid, electrolyte and glycogen loss (which is why pacing is critical) but the heat impacts the ability to effectively digest and absorb calories and fluids. Thus the greater risk of GI issues in higher heat environments.
As you prepare yourself mentally for your upcoming long distance event, keep in mind that working at a higher effort than your body can dissipate heat is going to produce a build-up of internal heat.
- Create a race strategy that will allow you to use your fitness in a smart way.
- Your fastest performance is the one where you minimize a massive slow down.
- Navigate the conditions you are given on the day, don't chase a PR or metrics. Listen to your body.
- Focus on what you can control. Make sure to "check-in" with yourself and respond accordingly.
- Take walk breaks (reset breaks) when you run. The longer you let the heat build up, the greater the slow down (and greater risk of GI issues).
- Back off the effort. Start out conservatively to minimize the risk of irreversible heat stress. Save your heart beats.
- Go in with no expectations. Race your own race.
- Go into the event well-hydrated and fueled so you are in the best state of health possible to perform in the race conditions. Have a plan - don't just figure things out as you go along.
- Fuel and hydrate consistently and frequently. Moderate amounts of fluids consumed frequently will digest and absorb easier than large or tiny amounts consumed periodically.
- Prioritize liquids over solids for easier digestion. As a general rule, the higher the carbohydrate content (and fat/protein) and lower the fluid intake, the slower the absorption rate.
- Focus on the process. Think of the race as a project, checking off to-do's and overcoming obstacles as you go through each mile.
- Keep yourself cool on the bike so you can start the run with a slightly lower (or normal) core body temperature. Use water from aid stations to douse the body.
- Your mour muscles demand more fuel (glycogen) in hot conditions. Muscles are more taxed which can affect efficiency and can also cause greater tissue damage.
- On the run, your stomach can only empty about 5-7 ounces of fluid every 15 minutes. If you drink more than you can empty from your stomach, you will risk a sloshy stomach. Also, if you only drink water, you risk diluting sodium in the blood. Make sure to rely on a sport drink throughout the race (that’s why I also suggest to wear a hydration belt on the run) and use water only for sipping and cooling.
- Use ice in your hands, on your head, around your neck and near your groin to help with cooling. Also use a cooling towel.
- Minimize the risk of a sunburn by using sunscreen.
- Wear a hydration belt with your sport drinks on hand so you can keep to your own drinking schedule.
- The harder the effort, the more your body temp will increase as more heat is being generated. The harder you push, the greater the increase in heat production. You will know when your body temp is increasing because you will feel yourself getting warmer. Control your effort to better manage your body temp throughout the entire race.
- Look for shaded areas on the course to avoid running in the direct sunlight.
- If you feel overly hot, dizzy or chills. Stop immediately, sit down and get yourself cooled.
If you found this information helpful and you'd like to learn more about sport nutrition (like should you concentrate your bottles during a race, how do I fuel before a long distance triathlon and more?) check out our team membership.