Keeping yourself hydrated during a long run can be challenging, especially in hot and humid conditions. It is important to pay attention to what and how much you are drinking before, during, and after running.

Maintaining water and electrolyte balance is of utmost importance during your run without which you may put your body at risk of dehydration.

Why do you need more water on a hot and humid day?

We need more water on a hot and humid day because we lose more of it through sweating and breathing. We sweat more in hot and humid conditions.

The body loses about 1 liter of water for every hour that we are active in high heat and humidity. This is because our sweat evaporates quickly, leaving us with about two-thirds less sweat to cool down, and it can drain the body of fluids quicker, especially when the air is dry.

Humidity is a measure of the amount of water vapor in the air. As humidity increases, the air becomes more saturated with water vapor and does not allow for evaporation to cool your skin.

In humid conditions, sweat does not evaporate as easily because there is more moisture in the air for it to mix with. This means that less sweat will come out on your skin and the fluid becomes less effective at cooling off your body temperature.

This is why people living in tropical countries often produce less sweat than those living in drier regions. Therefore, planning your fluid intake under humid conditions becomes even more important.

Drinking enough water will help you stay cool by cooling down your body temperature through perspiration. Water is also essential for maintaining homeostasis.

Science of homeostasis

Homeostasis is the body’s monitor for maintaining stability internally. When things are out of balance, homeostasis will balance them out. This includes things like temperature, weight, sleep, thirst, and hunger.

For example, to control the body’s temperature, it will produce sweat through sweat glands when the temperature is too hot, and shiver to generate heat when it is too cold.

Effect of humidity on sweating

Humidity affects how fast sweat evaporates from your skin. Sweat forms when blood vessels in your skin dilate and release fluid into the surrounding environment, causing them to swell and become visible on your skin’s surface.

The body’s core temperature is typically around 37°C. For the human body, the skin is the first barrier to heat loss. The skin can lose excess heat by evaporating sweat, which leaves behind a layer of cool moist air.

Evaporation happens when sweat meets dry surfaces. So, anything you are wearing or touching can have an effect on how quickly you sweat. When humidity levels are high, it takes more time for sweat to evaporate because these surfaces are already wet, which prevents further evaporation from taking place.

Effect of dehydration for runners

Runners lose a lot of fluids during their run through sweating. Sweat is made up of 99% of water and a little bit of salt, urea, ammonia, and protein. So, when you sweat, you lose a lot of water due to which you feel dehydrated and are unable to run at your best. Sweat loss higher than 2% of overall body weight may increase the risk of diarrhea, nausea, and gastrointestinal issues.

Studies show that runners who were dehydrated had an increased level of cortisol (stress hormone) in the body, leading to a reduction in testosterone, which is responsible for muscle growth. So, it is essential for runners to drink plenty of water before, during, and after their run for optimal performance.

However, water alone is not sufficient to meet the physical demands of a runner. Electrolytes must also be included along with water since they form a large part of hydration.

Importance of electrolytes

Electrolytes are a group of minerals that carry electrical charges within the body. They are considered essential nutrients for runners. Electrolytes are needed to make sure that muscles are getting the right amount of nutrients. 

Without electrolytes, muscles can become weak and lead to cramping or fatigue. A typical electrolyte drink consists of sodium, magnesium, calcium, phosphorus, and chloride.

While sweating during a long run, even if you continue to drink fluids, it can still lead to muscle cramps and other complications if electrolytes are not replenished. Water alone cannot meet this requirement. You may feel like your thirst never ends and think you should drink more water. Therefore, it is important to maintain a balance between sufficient water and electrolytes.

If you are a regular long-distance runner, you may consume a sports drink that contains the electrolytes that are listed in the below table: 

How much water should a runner drink on a hot and humid day?

Here’s an explanation of the ideal quantity of water that you can consider drinking during different phases of the run:

1. Before running

If you are doing a long run, ensure that you are well-hydrated. One indication to understand that you have hydrated well is if your urine is pale in color.

It is important to drink up to 500ml of water before running. However, stop the intake of water 30 minutes before the start of your run. This will prevent you from going to the bathroom during your long run.

Avoid drinking alcoholic drinks before your run because alcohol depletes your body of fluids. Moreover, it can restrict you from getting a good night’s sleep. So, it is better to limit or avoid alcohol intake before your run because you may feel dehydrated when you start running.

Also read: What to Eat Before, During, and After a Run?

2. During the run

Generally, you must aim to consume the equivalent quantity of fluid that you are losing via sweat.

You will need 200ml of fluids every 15-20 minutes during a long run for the first 60 minutes. It is also advisable to add 0.5g-7g sodium per liter of water to replenish the sodium lost through sweat.

Make it a point to carry enough fluids for the run. Carrying a handheld bottle pack or a fuel belt will be helpful during your run.

Also read: How to Breathe While Running?

3. After the run

A good strategy for figuring out how much fluid you should drink after your run is to weigh yourself at the beginning and end of the run. After you have seen how much fluid your body has lost, adjust your fluids accordingly.

Generally, a runner should drink up to 200ml-500ml of water every 20 minutes to replenish the fluid lost when running. If you are doing longer runs, it is prudent to have some other fluids to balance out your electrolytes. This is why sports drinks are recommended during long activities.

Also read: How to Recover Well from a Race?

Mistakes to avoid while running on a hot and humid day

1. Not hydrating enough

Drinking too little before your run can lead to dehydration, which can have adverse effects on your body. It may lead to headaches, fatigue, nausea, muscle cramping, and decreased coordination. It is also essential to stay hydrated to avoid heat-related illnesses, such as excessive sweating and heat stroke. 

Also read: What Happens to Your Body When You Do Not Drink Enough Water?

2. Hydrating more than you need

If you gain weight during a run, you are drinking more than your body needs. Drinking too much water without replacing sodium can lead to hyponatremia, which is a condition where the blood has too little sodium in it. This can upset the balance of electrolytes within your body, leading to dizziness, vomiting, and lethargy.

Also read: Hyponatremia in Runners: When Too Much Water Is Dangerous

3. Hydrating with wrong fluids

It is essential to avoid hydrating with the wrong fluids. For instance, drinking alcohol before your run may not be ideal as alcohol increases the risk of dehydration. Moreover, the consumption of alcohol results in sodium losses, which would further decrease blood volume and impair run performance.

Sports drinks can be helpful for runners. However, do note that not all sports drinks contain the essential amount of electrolytes required by runners.  Therefore, in this situation, it can be useful to include a salt tablet.

Caffeine consumption before your run may also have a negative impact because of its diuretic properties, which would lead to increased fluid excretion.

Maintaining a healthy fluid balance is important for runners to keep up with how much water they are losing during the run.

Drinking water at regular intervals will keep you hydrated throughout the run. So, plan your hydration much before your run and ensure to follow a balanced diet. 

References
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4. Shaheen, N.A., Alqahtani, et al. Public knowledge of dehydration and fluid intake practices: variation by participants’ characteristics. BMC Public Health 18, 1346
5. Maresh CM, Whittlesey MJ, et al. Effect of hydration state on testosterone and cortisol responses to training-intensity exercise in collegiate runners. Int J Sports Med 2006; 27: 765-70.
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