I talk about hydration with almost every Athletic Therapy patient I have. I drink a ton of water myself, so I want to spread the reasons why. If you are active…listen up! Studies show that hydration is the most important for endurance based events, as well as events consisting of complex tasks i.e. a team sport, executing a skill etc. Dehydration (hypohydration) can impair physical and mental performance, hence why completing a complex task (like in a sport) is also affected by hydration status.
Sweat loss, body mass and hydration all go hand in hand. The American College of Sports Medicine outlines that fluid intake should be enough to limit any body mass loss of less than 2% of the pre-exercise mass. Importantly, athletes should never gain body mass (by drinking too much water) during exercise, as this could lead to hyponatremia (excess sodium loss).
Many factors determine sweat rate: temperature, humidity and exercise intensity. Also sweat rate varies person to person. To determine how much sweat you have lost, you can weigh yourself (ideally nude) pre and post-exercise. According to Maughan & Shirreffs (2010) they recommend having a shower right before you weigh yourself and towel dry, then you can correct for hair wetness etc. Make sure you go to the bathroom prior to weighing yourself both before and after exercise. The more body mass you have lost after exercise, the greater the sweat rate and the more fluids you need to replenish. Many people are actually dehydrated prior to exercise and therefore, you are even more dehydrated after exercise.
Gatorade or carbohydrate drinks, should you drink them?
Our sweat contains a variety of electrolytes, especially sodium and chloride however the sodium loss is the most important to consider. Those who have high amounts of salt in their sweat may be at risk of exercise-related cramping; this would be an indication to consume an electrolyte/carbohydrate based drink. When should you drink it and how concentrated should the drink be? Studies show if you are exercising for longer then 2 hours, salt should be consumed during exercise to avoid hyponatremia (excess sodium loss).
However, it is outlined in the literature that fluid and sodium needs should be based on individual measurement of fluid and sodium losses and therefore, one regimen does not suit everybody. Some people excrete more sodium in their sweat than others, hence each individual need for salt is different.
A common way to see how much salt you sweat is by working out in a black shirt; wait for the shirt to dry and look for salt stains were sweat has evaporated. The more salt stains, the more salt you excrete! Those who lose more salt in their sweat are more susceptible to muscle cramping. So if you know you often experience muscle cramps, you likely lose a lot of salt in your sweat.
High sweat rate and/or high salt loss would indicate a need for a electrolyte/carbohydrate based drink like Gatorade, Powerade etc. But be careful because some people are more salt-sensitive than others. Also, if you don’t excrete a lot of salt in your sweat then you do not need a lot of salt replenishment.
A 2010 study investigating cyclists and their time of cycling onset to fatigue was the greatest when a dilute carbohydrate-electrolyte drink was consumed. Therefore, a dilute Gatorade or Powerade drink should be sufficient especially for endurance-based athletes.
Lets talk about pee
According to Maughan & Shirreffs (2010), the colour of our urine is determined by the amount of urochrome, which is a breakdown of haemoglobin (iron-containing protein found in all red blood cells). It comes from the processing of dead blood cells in the liver. When we ingest a lot of fluid and large amounts of urine is excreted, the urine is dilute and very pale in colour. When we are dehydrated and small amounts of urine are excreted, the urine is concentrated and solutes are excreted in a small volume and is dark in colour. Urine colour in the morning is the best marker for hydration status, however this can change greatly throughout the day. As a result, the variability in our urine throughout the day makes its impact on hydration status unreliable.
Take Home Message:
- Athletes should weigh themselves pre and post training sessions of different durations, intensities and in different climates. Then they can make reasonable estimates of sweat losses. Weight loss should not exceed 1-2% of body mass. If they lose more, they will know to drink more fluids.
- High salt losses contribute to muscle cramping. People who experience muscle cramping more often may benefit from more drinks with salt in it or an electrolyte/carbohydrate based drink and may require more salt in their food when sweat losses are high.
- People who are urinating less may be dehydrated. If urine volume is small and urine colour is darker, fluid intake should be increased. The aim shouldn’t be for urine colour to be as pale as possible.
One final thought: Individuals should be responsible for determining their own rehydration strategy, as a hydration schedule generalized to everybody is not fitting. Learn your individual sweat rates (or seek help from your Athletic Therapist or a local Exercise Physiologist to determine this) and implement the most appropriate drinking behaviour while estimating your need for water, salt and carbohydrate replacement. Stay hydrated!
Maughan, R.J. & Shirreffs, S.M. (2010). Development of hydration strategies to optimize performance for athletes in high-intensity sports and in sports with repeated intense efforts. Scand J Med Sci Sports. 20:59-69
Ross, K.A (2017). Nutritional Aspects of the Female Athlete. Clin Sports Med. 36: 627-653