Last week, I discussed day-to-day hydration needs and what to drink prior to exercise. If you missed it, click here. As promised, this week, I’ll discuss what you should be drinking during exercise to optimize your performance.

The goal of your fluid plan during exercise is to prevent a body weight loss of greater than 2%. For instance, if you weigh 150 lbs then you would want to lose no more than 3 lbs during exercise. The amount of fluids that this athlete drinks during exercise should be enough to prevent more than a 3 lb weight loss from sweat.

Sweat rates during exercise are extremely individualized and dependent on various factors. This is why there is no one size fits all hydration plan and why this plan changes from day to day (think summer versus winter). For instance, the mean sweat rate of half-marathon runners was found to be 1.49 L/hour compared to 0.37 L/hour in swimmers.

Calculating your sweat rate is not too difficult. All you need is a scale and some math skills. This will allow you to make your own individualized fluid plan for during exercise. However, you should not use one single sweat rate calculation to make a fluid plan. For better accuracy, track it over time and with exercise conditions similar to race day. For detailed instructions on how to do this, click here.

Translating your sweat rate into a fluid plan takes some simple math. For instance, if you found that you have a sweat rate of approximately 1.0 L/hour and you have a goal of a 2-hour half marathon then you would want to aim for 2 litres of fluids consumed across the entire race. This would equate to about 250 mL every 15 minutes. It is okay to end exercise in a fluid deficit, but we want this deficit to be less than 2% body weight loss. Going above this will likely impair your athletic performance and increase the likelihood of gastrointestinal symptoms such as the dreaded runner’s trots.

You’ll likely be shocked by the amount of fluids you need to consume to prevent dehydration during exercise. Remember, you have to train your stomach, just like you train your muscles for race day success. During training is the time to practice taking in larger volumes of fluid. As your stomach adapts, you will find reduced bloating and fullness during exercise, while allowing yourself to meet your hydration needs.

Stay tuned for next week’s newsletter that will highlight the final blog of my hydration series: what to drink during exercise. Want to learn more about using nutrition to optimize performance? I’d love to work with you to provide personalized nutrition advice to help you reach your goals. To learn more or to book an appointment click here.


Categories: Megan Kuikman

Megan Kuikman

Hello! I’m Megan Kuikman. I’m a Registered Dietitian with specialized training in sports nutrition. My goal is to help athletes and active individuals achieve a healthy attitude towards health, training, and food. I empower athletes to fuel properly for training in order to restore their health and enhance performance. You can get in touch with me at:


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