Racing can be hard enough on any day—and when you add heat and/or humidity, it can wreak havoc on your body if you’re not adequately prepared. Knowing how to race well in the heat can really set you up for success on race day. But before we look at the best strategies to prepare before and during, let’s first dive into some of the physiology involved in effective hydration.
Remember that water in your body is your means of dissipating heat—the blood circulates to the muscles to bring fuel and, at the same time, picks up metabolic by-products, one of which is heat produced through muscular contractions. Blood then circulates to the skin to offload the heat through several mechanisms, the most effective being evaporative cooling, also known as sweating.
As you sweat, you lose water from the blood (and as the plasma volume drops, the body pulls water from other spaces to try to keep blood volume up). This means if you are slack on your hydration, you compromise your blood volume, which means compromised blood circulation to the muscles and the skin—and thus less water for sweating. Not what you want in order to race well in the heat!
There are specific things the body needs to create a net water gradient in the small intestines (where 95% of water flux takes place). These key things are: glucose, sucrose, sodium, and on a smaller scale: potassium, magnesium, chloride, and calcium. Without glucose and sucrose, the constant flow of sodium and water into the body becomes rate-limited (i.e. slows down as the body tries to find glucose to work with the sodium).
Sodium intake is always a hot topic and athletes are always asking me how many salt tablets they should be taking in an event to race well in the heat. Let’s be clear here: The body has ample sodium stores, and the misconception is that you need sodium during training and racing to replace losses. You do not need salt tablets! Even as a “salty sweater” the sodium from the foods you are eating—and from your hydration drink, if you choose wisely—will ensure you have adequate sodium. Salt tablets contribute more stress to the gut than most people realize. When you ingest a high dose of sodium, you end up with some reverse water flux; water goes toward the sodium, so if you have a high concentration of sodium in the digestive tract, water will leach into the GI (gastrointestinal) tract, contributing to additional issues with gut sloshing and dehydration.
Managing the Heat
Before the gun goes off, there are a few things you can do to “pre-cool,” reduce your core temperature, and effectively delay the time it takes to reach a critical core temperature (i.e. fatigue) that will prevent you from racing well in the heat. These strategies can include a 10-15 minute pre-race swim in cool water, drinking an icy slushy, or for those lucky enough to have access to one, wearing a water-perfused vest can also help (not to be confused with an ice vest).
During your race, in an ideal situation you’d be slurping down an icy cold hydration drink that is 3-4% glucose/sucrose/sodium—but that obviously isn’t always possible. Anything you can ingest that is cold will help reduce the rate at which your core temperature is rising, keep you cool, and help you race well in the heat. Grab some ice water from an aid station and drink it down—also suck on the ice, but do not pour ice water on your head! (The ice water is too cold, the head is very vascular, so the cold of the ice will constrict those vessels, sending hot blood back to the core, but cool water on the head is fine). Cool water on your forearms is also a great way to off-load heat, as well as using UV protectant arm skins to prevent sunburn and to hold cool water against your forearms. Above all else, keep drinking—and do so often!