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Hydration Tips For Training and Racing

Hydration can be confusing for runners at the best of times, let alone during summer or training for races! We asked expert running coach, Anna-Marie Watson, to share her top hydration tips for trail runners.



If you’re running less than 60 mins and are fully hydrated it’s unlikely you need to take a drink with you. Beyond an hour make sure to test out what electrolyte products work for you. Endurance runners typically use 700 mg sodium per litre of fluid (though the sodium content of sweat ranges from 115 mg to over 2,000 mg). If you’re covered in salt at the end of a run - it’s a sign you’re a salty sweater! 

The Sweat Test

Runners lose between 400 and 2,400 ml per hour of exercise dependent on age, sex, running intensity and environmental temperature. Let’s call it on average 1,200 ml. Get to know your sweat rate with an at-home sweat test. Weigh yourself (obviously naked!); head out for a one hour run at race pace; weigh yourself afterwards. 

Side note: Make sure to pee before you run and towel yourself dry afterwards. Work out your difference in weight where 1 gram equates to 1 ml water lost. This knowledge is helpful to plan your during and post-race hydration. It’s usually impossible to remain fully hydrated whilst racing though the key is to ensure you rehydrate within 90 mins to 2 hours. 

Work out how to carry water

Whether you carry soft bottles in the front of your race vest, a water bladder, water bottle in a waist belt; a hand held bottle and/or soft cup for aid stations. Think about:

  • The capacity you’ll need to carry 
  • Distance between water sources
  • Ease of drinking from bottles / bladder and refilling 
  • Choose whichever solution is comfortable alongside all your kit 


Top Tip: it’s handy to choose two different coloured Soft Bottles - one for water and one for electrolytes.

Week before a race 

Stay hydrated

Focus on your daily hydration and start each morning with a glass of water and carry a water bottle around with you. Drink 1.5L (minimum), though your needs vary depending on physiological factors (genes, metabolic rate and body size) THEN lifestyle factors also exert an influence, for example take into consideration your consumption of caffeine or soft fruit. 

Hydration awareness

Be conscious whether you feel thirsty and notice the colour of your pee - aim for pale straw coloured urine throughout the day. If it’s getting darker - drink! 

Race plan

Prior preparation and planning prevents poor performance. Based on your training knowledge and experience create a hydration strategy that you know works for you. Take into consideration the race route, identify aid stations and other possible opportunities to refill e.g. shop, cafe, or tap.

Check out Harrier's handy printable Race Plan template available as part of their How To Run An Ultra guide.

During your race 

Drink to thirst

Keep hydrating from the beginning to the end. Think little and often which equates to a minimum 50 ml to maximum 250 ml every 20 minutes. 

Dehydration awareness

Know the signs and symptoms beyond fatigue, energy and stamina loss which can happen during a race (!). Notice if your mouth is dry; dark yellow urine; decrease in urination; muscle cramps and headaches. Chronic dehydration involves rapid heart rate and breathing, low blood pressure and sunken eyes. 

Hydration isn’t over when you reach the finish line

Make sure to keep hydrating once you’ve crossed that finish line. It can be tempting to celebrate your success - though keep it to one beer.  

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