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  • Writer's pictureRasa Nutrition

Exercise and Fluid Replacement Considerations

Updated: May 13

Contributed by Hannah Stoker

We sweat. When we do, water evaporates from the surface of our skin. It’s the bodies mechanism for cooling our core body temperature. During athletic performance, not only do athletes sweat and lose water volume in the body, but they also lose some electrolytes, mainly sodium and chloride. Those electrolytes are important for maintaining fluid balance in the cells of our body.

Have you ever wondered how much fluid you need when exercising? The answer is unique to you. The best fluid replacement strategy for each individual athlete considers your sweat rate, sweat composition, exercise intensity, ambient temperature, and humidity to determine the best approach for your body.

Fluid replacement is important for me as an athlete? It’s all about safety and supporting your body. In fact, a fluid replacement strategy is especially pertinent for the safety of athletes during long endurance or ultra-endurance training and races like the Ironman triathlon event. In training sessions or events that are much shorter in duration, athletes should aim to minimize fluid losses in order to optimize performance.

When your body loses large amounts of water during exercise, your blood volume is reduced. A reduced blood volume increases the cardiac output required to maintain athletic performance. An increased cardiac output elevates perceived strain on the body during exercise which increases core body temperature and impairs skeletal muscle blood flow. When your ambient temperature increases, your sweat rate increases, and this amplifies the effects of reduced blood volume if fluids are not adequately replaced. As your training intensity increases, your body’s demand for oxygen increases. This translates into an increased demand for blood to your muscles to increase oxygen plus an increased blood flow to the skin so that your body can offload heat. Thus, as training intensity is increased, the importance of fluid replacement to achieve adequate blood volume and flow is elevated.

What is the ideal fluid replacement strategy for me? As a starting point, Rasa Nutrition recommends that athletes consider determining their individual fluid loss during exercise by noting body mass before and after a training session at a given temperature. This can help mitigate variability from athlete to athlete in sweat rate, sweat composition, and training status and intensity. To prevent performance decline, athletes should aim to reduce body mass losses to less than 2% of the pre-exercise value by drinking sufficient water throughout performance. For athletes who lose substantial amounts of sodium in their sweat or for athletes participating in longer endurance events, consuming sports drinks, or electrolyte drink mixes, throughout the bout of exercise can be an important factor to increase water retention and encourage water consumption. A fluid replacement strategy can be refined during training, especially under the guidance of a dietitian, before being used in a competitive setting. Happy hydrating!


1. Burke L, Deakin V, eds. Clinical Sports Nutrition. 4. ed. McGraw-Hill Education Medical; 2010.

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