Hydration

Chances are every endurance athlete has experienced dehydration which impacted performance at some point in training or racing. Dehydration impacts performance because we have reduced blood volume, increased heart rate, decreased skin & GI blood flow, increased core temperature, and increased rate of muscle glycogen usage. 

Symptoms of dehydration while running include decreased performance, inability to hold paces, fatigue, GI distress <stomach sloshing, cramps, diarrhea, nausea>, increased perceived exertion, and muscle cramps. 

We often talk about ‘percent dehydration’ when looking at how dehydration impacts performance since total fluid loss impacts smaller and larger runners differently. Older research suggested anything over 2% dehydration decreased performance. However, a review of over 770 marathon runners found an average of 3.8% dehydration at the end of a marathon, with the range of 1.6 – 8% dehydration, with some of the faster runners ending the most dehydrated.

While percent dehydration is interesting, it appears that fluid needs for optimal performance are highly variable and start with understanding our own sweat rate, fluid needs, saltiness, and trial + error by performance.

Sweat rate is how much sweat we lose per hour while training. Sweat rates vary dramatically from person to person, as sweat rate is genetic. Average sweat rates for endurance athletes are 0.5 – 2.5 L/hr. We’ve seen sweat rates range from 0.5 L/hr to 4 L/hr. The difference between these two athletes’ hydration needs is astronomical. 

An individual athlete’s sweat rate also varies greatly throughout training related to temperature, humidity, heat acclimation, and clothing. Knowing how much sweat you lose in different conditions throughout your training allows you to create a plan to better manage your hydration to improve performance & recovery. 

Your sweat rate will change throughout the year. Test & re-test in different weather to get to know how your sweat rate changes. It will also change in different types of exercise. If you are a multisport athlete, knowing your sweat rate in each sport would be beneficial.

Once we know how much our body sweats in different conditions, we can adjust the amount of fluid we are drinking before, during, and after training to stay on top of hydration needs. Ideally, we break hydration into before, during, and after.

Sweat rate tells us how much fluid we lose. Sweat composition tells us what we lose in that fluid. Our sweat contains water, sodium, chloride, potassium, and calcium. Sweat composition is genetic and it is fairly consistent throughout your training. Sodium is the electrolyte lost in the greatest amount via sweat. The average athlete loses around 900 mg sodium per liter of sweat, with ranges from 200 mg – 2000 mg per liter reported. 

Sodium and chloride are the electrolytes lost in the highest quantities in sweat and account for the detrimental performance outcomes with dehydration. We also lose potassium, magnesium, and calcium in much smaller amounts, however, these electrolyte losses do not hinder performance. This is why we focus on sodium intake before, during, and after training and races. 

Just like sweat rate is different from athlete to athlete, sweat composition varies dramatically as well. Understanding personal sweat composition has been a game-changer for many endurance athletes. If you want to dive into this, email us at [email protected], and we can help connect you to a company that can help.

Have you ever noticed white crusty stains on your clothing or gritty white residue on your skin after training? This is the salt in your sweat drying as the sweat evaporates. As your sweat dries, if you notice minimal salt on your skin and clothes you likely have a low sodium concentration in your sweat. If you notice some salt on your skin and clothes, you likely have an average sodium concentration in your sweat. If you see very noticeable lines on your clothing and skin, you likely have a very high sodium concentration in your sweat.

Salty sweaters may experience GI issues, cramping, decrease in performance, and intolerance to training in the heat more easily than peers. 

Other signs, along with salty streaks, that indicate you may have a high sodium loss in sweat are frequent muscle cramps after heavy sweating, intolerance to training in the heat or feeling awful after, dizziness or lightheadedness at the end of training, your sweat stings your face and eyes, and cravings for salt. 

The CDC recommends that we eat less than 2300 mg sodium per day. A salty sweater loses this in an hour of running. As you can see, salty or heavy sweaters may need to add significantly more sodium into their day when training. It’s not uncommon for a heavy, salty sweater to need 2 – 4x the daily recommended amount of sodium. Add salt to your food. Try higher sodium electrolyte drinks. Choose saltier foods. And notice how you feel and recover. 

Salty sweaters training in the heat can benefit from taking a very high sodium supplement the night before big workouts and long workouts to hyperhydrate. This means our body holds onto extra sodium and fluid to act as a buffer to our hydration when we begin sweating in our next training session.