Matching your hydration needs to your run isn’t always easy. Overdo it before a race and you risk stomach discomfort or a loo stop. Run when your fluid reservoirs are too low, however, and your performance will be reduced and your run will feel harder.
Studies have shown that during prolonged exercise a two per cent loss of body mass can result in around a 20 per cent decrease in performance levels in temperate climes (like the UK) and up to a 40 per cent decrease in hot temperatures.
‘Water is needed to regulate body temperature and allow muscle contractions to take place,’ explains dietitian and sports nutritionist Linia Patel, a spokesperson for the National Hydration Council. ‘Drinking water before, during and after helps you to run more efficiently and recover better from sessions.’
Side effects linked with mild dehydration during exercise include increased feelings of effort, poor mental performance and cramp. Here’s what to quaff and when, for everything from 5K to a marathon.
For peak performance you should make sure you aren’t dehydrated or thirsty before starting a run, even if it’s only a 5K. ‘A tried and tested way to gauge your hydration status is to check the colour of your urine,’ says Patel. ‘Apart from you first pee of the morning, you should be looking for urine that’s a pale straw colour.’ With a 5K you probably won’t need to take fluid on board during the run itself, although you should listen to your body and do so if you feel the need. Water should be your drink of choice, as isotonic drinks don’t come into play until you’re running longer runs, lasting one hour or more.
For a 10K run, being well hydrated beforehand is again your main focus, with how much you drink during your run dependent on your thirst and the prevailing conditions. For this distance, plain water continues to be an effective fluid replacement, according to Patel. Sip, rather than gulp large amounts if you’re drinking while running and be aware you’ll always need more water in hot weather or at high altitude. However, drinking more than 750ml during a run that takes no more than an hour would be excessive for most people’s needs, even in warm conditions.
When the distances start getting serious, the need for adequate hydration is even more crucial. ‘Half-marathon and marathon runners have average sweat rates of 1 to 2.5 litres per hour,’ says Linia Patel. ‘Females may lose a greater proportion of body water volume, despite sweating less in the same conditions, while smaller athletes may sweat less due to a reduced body surface.’
A general guideline for hydrating before a long distance run is to drink around 5ml water per kg of body weight two to four hours beforehand (say 250-350ml for an average female), leaving time for your body to excrete what you don’t need before you run. In the 10-20 minutes before you set off, some further regular sips of water can be a good idea.
During the race itself, a rough guideline is to take in 3-4ml of fluid per kg body weight (say 150ml – 250ml) every 20 minutes or so, although you may want to wait until you have the first few miles under your belt before getting started with this regimen, depending on how you feel. As for what to drink, isotonic drinks can be a better bet than water for half and full marathons, or alternatively you may want to stick to water and add in some gels.
Whatever fluid strategy you go with, the most important thing is to make sure you’ve practised it several times before a big race day to find what works for you.