Hydration to Support Performance
For marathoners, triathletes, endurance athletes, or anyone who does aerobic activity for extended periods, staying hydrated is crucial to your body's ability to perform. There is no shortage of articles and supporting evidence reminding us to hydrate and replenish our electrolytes. The question is, how much is enough? Each of us has a different output during exercise, and a number of factors lead to our bodies sweating at different rates. Research has shown that individuals typically can sweat at a rate of .5 to 2.0 liters per hour of activity (Smith et al., 2021). This means that one person doing the same activity as another could, in theory, lose four times as much fluid. To complicate this further, sweat electrolyte concentrations vary considerably from person to person. This all points to the importance of developing an individualized fluid replacement strategy.
How do you determine the volume of fluids lost to rehydrate properly?
To maintain adequate hydration levels, keep your fluid losses below 2 percent of your body weight during activity (Judge et al., 2020). However, even a 1 percent decrease in body mass through fluid loss can lead to increased heart rate and core temperature, reduced cognitive function, and the time it takes to reach exhaustion. With this in mind, understanding how much fluid you lose during extended ( >60 minutes) periods of exercise is the first step to forming your rehydration plan.
An effective way to estimate your fluid needs is to monitor changes in body mass when exercising to determine your sweat rate (Smith et al., 2021). To do this:
1. Record your weight before your exercise session. If possible, weigh yourself without clothes on.
2. Keep track of the amount of fluids you consume during exercise.
3. Weigh yourself post-exercise. Also without clothes if possible.
4. Add your post-exercise weight to the amount of fluids you consume.
5. Subtract this total from your pre-exercise weight.
6. Divide this total by the number of hours you exercised. This will give you your estimated sweat rate.
7. Repeat this process a few times and determine the average for these sessions.
Environmental factors and exercise intensity level play a big part in your sweat rate, so make sure you have similar conditions during these sessions, including temperature, duration of the session, and exercise intensity.
Hydration strategies tips pre-exercise:
● Drink 16-24 fl. oz. of water within the 2 hours beforetraining (Apostu,2014).
● Within 20 minutes before exercise, consume another 7-10 fl. oz. of water.
During exercise:
● If you have lost more than 2 percent of your body weight, consuming 6 to 10 ounces of fluid every 10 to 20 minutes is a good rule of thumb (Smith et al., 2021).
● If you have lost less than 2 pounds, consuming 16 ouncesper hour should be sufficient.
● Avoid overhydrating, as it can lead to serious health complications, such as Hyponatremia, which results from a sodium imbalance and excess fluids flooding the cells.
Post-exercise:
● You should aim to consume 16 to 24 ounces of fluid for every pound of body weight lost during exercise.
● Avoid drinking cold drinks (below 50 degrees Fahrenheit), as they can reduce your thirst and inhibit your ability to consume the proper amount of fluid during recovery.
How do I maintain my electrolyte levels?
As your sweat rate increases, so does your loss of sodium and other essential electrolytes. Electrolytes consist primarily of sodium, potassium, chloride, magnesium, calcium, phosphate, and bicarbonate. Our kidneys maintain optimal levels of these minerals, but the regulator process heavily depends on our dietary intake. This increased loss of electrolytes when we sweat and urinate disrupts these levels. Here are a few tips to maintain optimal electrolyte levels:
Pre Exercise:
● Hydrate with a sodium-rich drink or food that contains salt accompanied by water. This will help support fluid retention during exercise.
● Avoid drinks high in sugar.
During Exercise:
• To replenish electrolytes, use electrolyte tablets, salt capsules, or sports drinks at a rate of 300 to 450mg of sodium per 16 ounces of fluid (Apostu, 2013).
● Short low-intensity workouts (< 45 minutes) shouldn’t require electrolyte replenishment other than what a nutrient-rich diet supplies. Drinking water should be sufficient.
Post Exercise:
● Begin rehydrating by consuming a carbohydrate-containing drink to stimulate the intestinal absorption of water(Millard-Stafford et al., 2021).
● Consistent salt deposits on your clothing or skin indicate a high sweat rate and sodium concentration. If this happens consistently, consider increasing your electrolyte intake during exercise (Linder et al., 2022)
How does thermoregulation influence our sweat rate?
Our body has between 2 to 4 million eccrine sweat glands that regulate our body temperature in reaction to thermal changes, most notably when our core temperature increases (Baker, 2019). The rate at which these glands secrete sweat and how densely concentrated they are is a deciding factor in the volume of sweat we produce to regulate our internal temperature. It is widely accepted that as our sweat rate increases, so does the amount of sodium in that sweat. This is because the glands cannot reabsorb sodium at the rate at which it is being excreted. The most effective way to decrease the rate at which your body loses sodium when sweating is heat acclimation. To truly become acclimatized, it can take up to 2 weeks of continuous exposure to the environment you are acclimatizing to. The takeaway here is not that you necessarily need to acclimate to each environment you are exercising in, but instead, be prepared for a higher volume of fluid loss and lower levels of electrolyte retention when exercising in a higher-temperature environment. Use the recommendations above to adjust accordingly.