Updated for 2024

Training and racing in cold weather is entirely different than training and racing on hot days.  Strange things happen in hot conditions;  some athletes thrive while others fall apart.  Your nutrition program has a lot to do with how well you handle extreme conditions.  Dehydration, cramping, and GI distress can wreak havoc on your performance, so it’s important to pay attention to your sweat rate.

In very arid environments (like in Arizona and Utah), sweat can evaporate almost immediately, which can make it difficult to figure out your sweat rate.  In dry conditions-your sweat rate can be at it’s highest-even though you don’t see or feel any moisture on your skin. On hot days, hydration (the consumption of water and electrolytes) is always more important than your caloric intake. This is not to say calories are not important, but the consumption of calories without a proper hydration strategy will, ultimately, lead to disaster.  It’s important to determine your hydration requirements before calculating how many calories you should consume.

Sweat is your body’s mechanism to cool itself in hot environments. The more trained you are, the better your mechanism to sweat and cool yourself becomes. If you have a high sweat rate, it’s a sign that your body has acclimated to the heat. To sustain a high sweat rate, which is ultimately what you want in hot conditions, you have to maintain the appropriate amount of fluid.


Dehydration significantly reduces your ability to absorb calories and nutrients.  There’s a direct correlation between dehydration and your body’s ability to absorb nutrients.

Even a 1% drop in internal fluids requires your heart rate to increase in order to sustain an adequate sweat rate.  Obviously, not what any endurance athlete wants to happen.

If you suffer a 2% drop in total internal fluids, you’ll experience a serious decrease in your performance. Best case scenario, you’ll be diminished to “the walk of shame.”

You could even suffer from heatstroke. Hydration is critical to performance, especially in hot conditions.


We’ve all experienced it, in some variation.  It’s basically a “rite of passage” for any serious endurance athlete who’s ever pined on a number.  Everything seems to be going well, and then it hits.  If you’re lucky, you can get through it and struggle to the line.  Those are fortunate days.  But, more often than not, it’s the end of the road- and it’s not pretty.

We’re talking about cramping; biblical cramping.

There’s also the danger of gastrointestinal distress, which can be a life-changing event.  We’re talking about nausea, vomiting, and explosive-diarrhea of the legendary caliber.

They’re the stories you tell your friends when they ask you: “what’s the worst thing that could happen?”

Most athletes prioritize caloric intake and consume water arbitrarily without considering concentration percentages or osmolality, which is exactly what you shouldn’t be doing. 

The most important consideration, when racing on hot days, is hydration.  If you don’t make sure your hydration requirements are being met before consuming additional calories cramping, dehydration, and GI distress can wreck your day.

You probably won’t experience cramping or dehydration issues when training or racing for an hour or less. For longer sessions, however, it’s essential to stay on top of your hydration and electrolyte consumption. At First Endurance we recommend a balance of all five electrolytes (sodium, potassium, calcium, magnesium, chloride) in order to ensure proper muscular contraction and cellular respiration. When electrolytes are in balance, performance improves and the risk of cramping is eliminated.

Remember: training and racing in the heat will most likely be derailed by dehydration way before it’s affected by a nutrition bonk.

Because nutrition absorption gets compromised significantly without the proper hydration, it’s paramount to focus first on hydration and then on calories. Every athlete responds differently in the heat.  In extremely hot and long sessions, it’s not out of the question for some athletes to push 40-50 ounces of liquid per hour to sustain efforts, while others can get away with as little as 24-30 ounces. 

TIP:  On hot days we recommend drinking 21oz fluid for every 100 calories. If you know you will only consume 42oz of fluid per hour, then your maximum caloric intake during exercise should be 200. Attempting to force calories in without proper hydration is a recipe for gastric distress, cramping, and poor performance.


It’s always best to test your hydration and fueling strategies in training in order to figure out what works best for you. As the duration of training and racing increases, it becomes more and more important to pay attention to your fluid and caloric intake so you can balance the two appropriately in order to ensure success. Only consume the maximum calories that match your hydration consumption.

Your pace also affects how many calories you need.  A threshold pace will require significantly more calories than a slow pace, and thus, significantly more fluid.

You should change your hydration and fueling strategies during your training or racing as the temperature and/or pace change. If it starts out cold and heats up as the day progresses, be sure to adjust your caloric intake and hydration accordingly.

April 20, 2021 — First Endurance
Tags: coaching

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