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As the weather heats up, dehydration can unexpectedly hit, even on shorter runs.

Here's everything you need to know on why hydration is important, the dangers of dehydration, and a comprehensive guide to sports drinks to keep you running easily and healthily whatever the temperature.

Why is Hydration Important?

Staying well-hydrated is key for keeping your body functioning properly, not to mention keeping you at the top of your running game.

In Summer this is especially important; we lose most our water through sweat, which as it evaporates from our skin, takes the heat with it helping us to cool down. 

When the humidity rises, it reduces our body's evaporation rate because of the water already in the air, leaving you soon feeling hot, sweaty, and needing to slow down.

The more dehydrated you become, the harder your heart needs to work to pump your blood around your body. This is calleIf the air is dry, the sweat evaporates much more quickly, almost as you're producing it, so you're more likely to become dehydrated cardiac draft; your heart rate increases over the course of the run, even when your intensity is the same. 

The heat and the sun also increase your body temperature, as soon as you start feeling too warm, your running will feel difficult.

Even if you're properly hydrated, it's normal for your pace to slow down as your internal temperature rises. The general rule is for every 5°C, above 12°C, the temperature rises, your marathon pace can increase by 1.5-3%.

Add to that the effects of dehydration and that PB you're chasing could suddenly feel a long way away.

The Dangers of Dehydration

Although severe dehydration is rare, running in the heat might cause you to experience some of these common symptoms: 


The most common signs of dehydration include fatigue, headaches, dizziness, and decreased coordination. After you run ensure you're drinking enough fluids.


Loss of electrolytes from sweating can cause muscle spasms and cramping during your run but also in the hours after. Although not serious, ensure you're staying hydrated and eat foods high in potassium like sweet potatoes, avocados, and bananas.


Defined by dehydration, headaches, nausea, and a core body temperature of up to 40°C, heat exhaustion is common in runners who haven't yet adapted to the heat.


Heatstroke is dangerous as your core body temperature hits over 41°C. Symptoms include disorientation, confusion, poor balance, lack of sweaty and clumsiness. If you start noticing any of these symptoms seek immediate medical attention.

A Runner's Guide to Sports Drinks

Plain water often passes through the body too quickly, and without the necessary sugars needed to start your recovery process. This is where sports drinks come in.

Most energy drinks contain a combination of quick and slow releasing sugars to provide both fast acting and sustained energy as well as high amounts of electrolytes such as sodium, chloride, and potassium to help replenish what you lose.

Generally, the higher the carbohydrate content of your drink, the slower the absorbtion rate into your body so choosing the best sports drink to maintain the best hydration and electrolyte levels during a run can be tricky.

Sports drinks are split into three catergories; which one you go for depends on whether you're rehydrating or replenishing your energy, before, during, or after you run:


Isotonic sports drinks contain mostly electrolytes and are usually around 6-8% carbohydrates. They have a medium absorption rate, taken up by the body about as quickly as water, but with added energy. These are the most common sports drinks on the market such as Lucozade, Gatorade, Powerade etc. and are ideal for during a longer run or endurance event. Try diluting them with water or usually specialist electrolyte tablets to help you quickly replace lost salts and minerals and rehydrate effectively. 


Hypotonic sports drinks contain the highest amount of electrolytes but with less than 6% carbohydrates. If you're running in hot conditions or a challenging race where rehydration is the most important factor hypotonic drinks have the fastest absorption rate so are best for you.


Hypertonic drinks will contain a high amount of calories and are ideal for refuelling after you exercise. Liquids such as fruit juice are hypertonic and are the least absorbable of all three catergories with over 8% carbohydrates. Avoid these high sugar drinks before you run as you're more likely to  become fatigued once the energy wears off. 

Water and isotonic or hypotonic sports drinks don't contain enough of the sugars and electrolytes  your body needs for recovery and, because of their high water content, are absorbed into the blood stream at a much quicker rate, increasing your risk of oversaturating your body with water.

Instead, go for a hypertonic drink with a 4:1 ratio of carbohydrates to protein for best running recovery

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