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July 6, 2016 Comments (0) Featured, Nutrition

It’s hot outside. Am I right?


Thank you to Gu Energy Labs for their continued support of this sponsored content.

Author: Heidi Strickler

Research shows the number one factor in athletic performance and success in competition is not fitness, nutrition, gear, speed work, or endurance. It’s body temperature. Body temperature affects our rate of perceived exertion, muscle contraction, neurological function, digestion, mental focus, VO2max and lactate threshold. So why am I, a Registered Dietitian, telling you about the role of body temperature over nutrition in performance?

While you cannot control the climate in which you train, you can control your nutrition, which can ease and even negate the negative effects of heat and humidity. Leave temperature regulation to the cup of water at the aid station or that mountain stream in the canyon.

Fueling Focus: For calories, fluids, and electrolytes, the goal is replenishment, not replacement. Focus on how much our body can absorb and use versus the amount of calories, fluid, or electrolytes lost. Aim to take in 20-40% of your expenditure.

Calorie Needs: 240-280 calories/hour for the average (160lb) athlete in moderate (70°F) temperatures for any effort over two hours.* Smaller athletes may need less, larger athletes may need more. Trying to take in all you burn (average of 800 calories/hour) is absurd from a digestive and efficiency standpoint. Our body fat stores (50,000-100,000 calories) can easily satisfy the gap between what is burned and what the body can absorb.

* Due to the jarring, runners do best with 30-50% fewer calories than the recommendation

Fluid Needs: 16-28 ounces/hour. One of the most common causes of swelling and stomach upset in the heat is excessive water intake. Our body cannot efficiently absorb hypotonic fluids (fluids with a lesser concentration that our cells), such as water. In exercise, use water primarily to follow solid fuel, gels, or concentrated caloric fluids, such as Gu Brew® or Perpetuem®. The rest of the time hydrate with electrolytes.  Many athletes gauge hydration by urine color or frequency, which can be misleading. Poor absorption results in excessive urination, leading to think we are properly hydrated.  Drink cold fluids as much as possible; they are better absorbed and also help internal cooling. 

Electrolyte Needs: sodium chloride 240-280mg/hour, but don’t supplement with sodium alone. Using salt tabs alone overwhelms the body’s regulatory system and actually results in your body increasing salt losses in your sweat. Look for an electrolyte replacement with calcium, magnesium, potassium, chloride, manganese, and sodium. 

How does climate affect these numbers?

Cold temperatures: increase calorie needs, decrease fluid needs. Don’t forget about electrolyte replenishment though, which is easy to do when we don’t sweat as much.

Hot temperatures: decrease calorie needs, increase fluid needs, increase electrolyte needs.

Humidity: makes it harder for our body to naturally cool itself through sweat because our sweat does not evaporate. Because there is less evaporation, yet it is still hot and you are still sweating, it is easy to overconsume water and end up retaining fluids. In humid climates it is especially important to cool the skin as much as possible, but also to focus on electrolyte intake rather than water alone.

What else can I do?

  • The average athlete will lose one liter (32 ounces) of fluid/hour exercise – it is important to know your personal fluid losses and hydrate accordingly.



Heidi Strickler, RDN CD

Registered Dietitian Nutritionist
Sports & Performance Nutrition
Multisport Director
Group Fitness
Experience Momentum Physical Therapy, Nutrition & Fitness
4030 Alderwood Mall Blvd. Lynnwood, WA 98036
P: (425) 776 – 0803
F: (425) 776 – 0813
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