Staying hydrated, while important for humans at all levels of activity, is especially important for athletes during vigorous exercise. The key to any hydration process is fast absorption of water and electrolytes at the intestinal cells. Electrolytes are key for maintaining fluid balance, which is what exercise “hydration” is all about. The most important ones to consider are sodium and potassium for fluid balance. You’ll often see magnesium with calcium added too, and this is for muscle function (including the intestines). Before we dive into the different types of fluid you can drink to stay well hydrated (for training and life), let’s first look at why you need them:
Why do you need fluids?
Fluids are essential to regulate your body’s temperature, transport nutrients and oxygen around the body and act as a medium for cellular reactions to occur. By drinking adequate volumes of fluids, you can meet your body’s water needs and:
• Reduce the risk of heat illness
• Reduce fatigue so you can have sustained energy throughout a training session or race
• Improve your performance by preventing and/or reducing dehydration
Dehydration is the loss of body water, mainly through sweating. With the loss of body water, your heart must work harder and your body’s ability to regulate temperature is impaired, and both of these are key factors in decreased performance. By keeping your body water up, you have less stress on the body so you can perform well. And while you want to replace lost fluids with water, you also want to include some electrolytes too, so let’s look at how best to do that.
Should you drink water, electrolytes, or both?
Water with a small amount of added sodium is a good option for lower intensity training that lasts less than 90 minutes, or competing for less than an hour (providing you are well fed prior to competition). All body fluids contain sodium with water, so the addition of sodium helps the water get to where it needs to be: out of the stomach and into the blood. When training or competition lasts for longer periods or is high intensity, you will need the boost of glucose, sucrose, and electrolytes to facilitate fluid absorption; plain water is not the best option. For sessions up to 90 minutes, 1/16th tsp of salt and 1tsp of maple syrup in 16oz of water will do the trick (this yields 250mg sodium, 4g carbohydrate, ~1.5% solution).
Most of the electrolyte drinks that are currently available have a 6-8% carbohydrate solution that includes fructose and maltodextrin components. One issue with this higher concentration is that it causes a water influx into the small intestines. A fluid solution of sucrose, glucose, and sodium mixed at a 1.5 – 4% carbohydrate concentration has been shown to maximize fluid absorption. This percentage keeps osmolality low which allows for faster emptying out of the gut and greater fluid absorption in the small intestines. Optimal electrolyte drinks are specifically designed to replace fluid and slow dehydration during exercise. (Note: for best performance, think: real food in your pocket, hydration in your bottles.). Ideally, for maximum fluid absorption you want to drink a 1.5-3.5% glucose and sucrose solution with sodium citrate and potassium chloride or citrate, magnesium, and calcium.
How much fluid do you need?
Unfortunately, there is no one-size-fits-all answer here, as fitness status, environment, training history and plan, as well as sex differences, all influence how much fluid you need. Generally, if your urine first thing in the morning is a relatively pale yellow color, you are off to a good start. Throughout the day, eating watery fruits and veggies, drinking tea, water, and low carbohydrate electrolyte drinks will help keep you hydrated. Afternoon (~3 p.m.) tiredness is often due to low body water and a drop in core temperature, so drinking a warm drink (e.g. tea or herbal tea) will help hydrate you and bring up your core temperature, reducing the fatigue.
Before training: In the 90 minutes leading up to your training session, if you are low on body water (based on thirst and/or urine color prior to the session), you need to drink as much as is comfortable of low-carbohydrate fluid. If it is a hot environment and you are not used to the heat, you could also consider a sodium fluid load (e.g. drinking miso soup or products such as The Right Stuff, SkratchLabs Hyper Hydration, or Nuun’s Podium Series Prime).
During training: Similar to pre-training needs, what you drink during your session depends on several factors such as temperature, environment, time of day, intensity of training, and sex differences. It is always important to go into a race or training situation well-hydrated, as it is much easier to come back from a low sugar “bonk” than it is to come back from dehydration (with a bit of food it takes a few minutes to come back around after a bonk, but it takes several hours for the kidneys and hormones to kick in for fluid balance after getting dehydrated). Your fluid intake during training should allow you to maintain effort towards the end of session. For sessions of 90 minutes or under, you can use water with a dash of salt and maple syrup. For sessions longer than 90 minutes and/or in the heat (looking at you, hot yoga!), then you will want to use a functional hydration drink (electrolyte drink) and sip early and often. Note that drinking to thirst is not a great measure as your thirst sensation becomes muted during exercise and by putting fluid on the tongue, you can “kill” feeling thirsty.
After training: After you exercise, slow rehydration over the course of two to three hours is the best option. Quickly guzzling back fluids in large amounts may cause a pressure response to make you pee out more than you absorb. Options for rehydration include your protein drink, watery lightly salted fruit (eg watermelon), or more of your electrolyte drink.