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I’m relatively new to triathlon and to serious training. Over the past several months I’ve been making steady progress, and recently I’ve noticed that I’ve started sweating more. The conditions (temp and humidity) are about the same as they’ve been, but I’m sweating a lot more. Does that mean I’m getting more fit?

– Jackie Gallagher, training for my first Ironman!

Jackie,

The short answer to your question, assuming that the environmental conditions have been roughly constant, is yes. Improving fitness impacts the way your body works in a wide variety of ways, and your sweat response to exercise changes as you become more fit because you’re increasing the workload your body has to be able to handle.

Sweat is one of your body’s primary means of preventing your core temperature from rising to dangerous levels. During exercise, the majority of the calories you burn actually generate heat instead of powering forward motion (sorry, but that’s just the way it is). In fact, on the bike you are only about 20-25% efficient, meaning 75% of the energy you produce becomes heat. That heat has to be dissipated, so your body dilates blood vessels near the skin to carry some of that heat away from your core to areas where cooler air flowing over the skin can carry away some of the heat. Sweat makes the cooling process work even better, because as sweat evaporates off your skin it takes a lot of heat with it.

As you become more fit, you are able to work harder. You generate more power on the bike and maintain a faster pace on the run and in the water. But the ability to work harder also means you have the ability to generate a lot of heat in a very short period of time. You also have the endurance to sustain exercise longer, meaning you have the capacity to generate heat for a longer period of time. Your body has to adapt to these demands in order to keep your core temperature stable. Here are a couple of ways it does that:

You start sweating sooner: Your body’s sweat response gets quicker as you gain fitness. This means you’ll see sweat appearing on your skin sooner after you start exercising than you did when you were a novice. These days, when you start warming up your body knows what’s coming next, so it ramps up the cooling process more quickly to stay ahead of the rise in core temperature. Your sweat volume increases: When the house is on fire, you open up the spigots and get as much water on it as you can. For the fire within, we don’t want to extinguish it but we need to control it, and the more sweat you get onto your skin the more likely you are to be able to keep core temperature from rising out of control. So your body becomes better at creating sweat. You lose fewer electrolytes per unit volume: As your body is adapting to sweat more and sooner, it also changes the composition of sweat so that you retain more electrolytes than you used to. You’ll still need to replenish electrolytes during exercise, but this adaptation helps to keep the electrolyte requirement manageable.

Fit athletes sweat more because they need to. They generate more heat and have to produce more sweat in order to maximize their evaporative cooling capacity. That means fit athletes have to consume more fluid so you have more to contribute to sweat. But sometimes sweating isn’t enough, or sweat might be enough to keep you moving but you could optimize your performance by helping your body stay cool. That’s where hydration, apparel choices, ice socks/vests, cold sponges, etc. come into play. Here are a couple of things to keep in mind:

Hydration is your source for sweat: The better you hydrate – during exercise as well as throughout the day – the more efficient your body will be when it comes to sweat production. Remember, when there’s not enough fluid to go around, your body starts an internal competition for resources, and all systems experience diminished performance. You don’t absorb and digest food as well, your muscles don’t function as well, and you don’t regulate core temperature as well. Evaporative cooling works just as well whether it’s your sweat or bottled/tap water that’s evaporating off your skin. Even if you’re well hydrated, it’s a good idea to dump water over your head and body during training sessions and races in hot weather. You’ll make your body’s job a bit easier by slightly alleviating the demand for sweat. Ice socks work the same way; the ice absorbs heat from your body to melt the ice, and then the water carries away additional heat as it evaporates out of clothing or off your skin. Electrolyte drinks or carbohydrate/electrolyte drinks should be a part of during-exercise nutrition strategy whenever your workouts are going to be longer than 1 hour. For workouts shorter than an hour, electrolyte drinks may still be somewhat helpful, but generally, you’ll start short workouts with enough carbohydrates and electrolytes on board to complete a high-quality one-hour session.

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