How to Stay Hydrated on a Trail Run

How to Stay Hydrated on a Trail Run

How to Stay Hydrated on a Trail Run

Written By: SportsShoes

One of the key commandments for all runners, the importance of staying hydrated during exercise is second to none. Put simply, if we fail to maintain adequate levels of hydration, this impacts on our performance and recovery - and can even have serious health implications. A hydration is strategy is all the more important for trail runners, who need to minimise risks when running in remote areas where help might not be easily at hand. Here’s how to stay hydrated on a trail run.


Around 70% of the body is made up of water and it is vital for essential bodily functions and biochemical processes. We lose water through urine, breathing out water vapour and importantly for all runners – through sweat.

Why is this so important when we’re running? When we run the body uses water as a coolant. The body’s temperature rises, triggering the body’s cooling mechanism, and signalling to the brain to increase sweat production to help prevent overheating. As a consequence, blood volume drops, less blood returns back to the heart, the heart pumps out less blood and less oxygen returns back to the working muscles. This results in an increased heart rate, onset of fatigue, loss of performance and eventually exhaustion.

Research shows that a loss of fluid equating to 1-2% of bodyweight while exercising can impact significantly on performance. And it doesn’t stop there. Progressive dehydration can eventually lead to cramps, headaches, and nausea, heat exhaustion and eventually to potentially fatal heatstroke.

This makes it important to replace lost fluids as quickly as possible and ensure you’re properly hydrated before, during and after your trail run.


When we sweat, we don’t only lose water. We also lose electrolytes, including chloride, calcium, magnesium, sodium and potassium and at the same time, glycogen stores become depleted. Sports drinks contain differing levels of fluid, electrolytes and carbohydrates and are optimised to effectively replenish these supplies during and after exercise.

Isotonic drinks:

Containing a similar composition of salt and sugar to the human body, isotonic drinks are easily absorbed and an effective way of rapidly replacing lost fluid and boosting glycogen stores during exercise, both quenching first and delivering energy. This makes them perfect for endurance events and other prolonged exercise.

Hypotonic drinks

Containing less than 4g of carbohydrates, hypotonic drinks are designed as a thirst quencher and are optimised to be quickly absorbed by the body. They deliver little in the way of energy but are more easily taken on by the body than water alone, making them perfect for athletes who need fluid without the carbohydrate boost.

Hypertonic drinks

Typically containing more than 8g of carbohydrates, hypertonic drinks are usually used post exercise to replenish carbohydrate stores, but are more difficult for the body to absorb than other sports drinks. They can also be taken on during ultra distance events to meet the demanding energy requirements, but must be taken alongside an isotonic drink to replace lost fluids.


Sadly, there’s no cut and dried or easy answer to this. How much you’ll need to hydrate on your trail run depends on a number of factors including age, gender, how much you sweat, temperature, intensity and training distance. That said, there are some basic guidelines you can follow:


If you wait until during your run to think about hydration, you’re on a straight path to becoming dehydrated. Nor is gulping down water an hour before your run ideal – your gut can only absorb so much water and you’ll end up heading out bloated and uncomfortable – not to mention making needing a bathroom break more likely during your run.

Instead, aim to stay continuously hydrated as part of your day to day lifestyle. For most people that means drinking around 1.5 to 2 litres of water daily (around 6 glasses of water).


Runs under 30 minutes:

Unless it is very warm, or you are running at high intensity you shouldn’t need to take on fluid during your trail run. Rehydrate with water after your run.

Runs 30-60 minutes:

As above, but rehydrate after your session with water and a carbohydrate based sports drink

Runs 60 minutes plus:

Take a sports drink containing water, carbohydrates and electrolytes. You should aim to rehydrate approximately every 20 minutes, taking on 30-60gm of carbohydrate per hour.


Again, these principles are a rough guide only, and you should take account of individual factors such as how much you sweat, the weather and exercise intensity to find a formula that works for you.

While you should aim to replace 80-100% of lost fluids, it’s important to know that it’s possible to overhydrate, potentially leading to the dangerous condition hyponatremia – or “water intoxication” where the body’s sodium levels become dangerously low.

As a guide, you can use the “pee test” whereby your urine should be the colour of pale straw. You can also work out your rough sweat rate by weighing yourself before and after your run. While you should aim to replenish fluids lost on your run, if you’re gaining weight, you’re more than likely taking on too much.

Hydration Packs

How to best to carry fluids on a trail run? Ideally, you need to be able to take on water quickly and easily without needing to stop, causing zero interruption to your run.


Probably the best option for trail runners because they are so easy to carry, hydration packs are backpacks containing a bladder with an easy-grab hose and valve allowing you to take on water quickly and easily while you run. Some also feature extra storage capacity, allowing you to take extra clothes, nutrition and other supplies for long runs, and range from 20 litre backs through to super-light hydration vests which store a bladder only – making them ideal for lightweight, distraction-free running.


Sitting on the waist, these belts allow you to store multiple water bottles on the run. Many packs also feature extra storage for key essentials such as your keys, phone and gels, while keeping your hands free as you run. These packs are designed with an anatomical fit, to minimise movement and bounce while you run.


You can also opt for a running-specific hand held water bottle. These are designed with an easy grip and some include a wrap around strap for extra security. The negative side to a hand held bottle, is that your hands aren’t free, which can be important when you’re running over uneven trails and rough terrain with an increased likelihood of tripping or falling.


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