You’ve been training hard all year for the big event – it could be a marathon, a cycling race, or any long and hard fitness challenge – and the glycogen-loading plan is in place. But let’s not forget about hydration because it’s an equally important part of race day preparation and you’ll need to create your individual plan.

I use the guidelines below when preparing or helping others to prepare for an event. The idea is to prevent dehydration by good hydration before, during and after the event.

Before you start

You’ll need to drink at least 500-600ml (5-7ml per kilogram of body weight) of water or a sports drink 2-3 hours before the event starts.

Drinking this amount several hours before exercise allows for fluid absorption and allows urine output to return to normal levels before you start running, cycling or whatever.

Then, immediately before the race or event commences, drink 200-600ml (5-8ml per kg of body weight) of fluid.

Now it’s time to hit the road…

During the event

While you’re running or cycling you need to get into a pattern of drinking at regular intervals rather than large volumes in one hit – ideally at a rate that matches the rate of your sweat loss. 

Remember, thirst isn’t always a reliable gauge of your body’s need for water. The goal of drinking during exercise is meant to prevent dehydration, and by doing that you’ll avoid a reduction in sporting performance. 

Sports drinks are the best option during events that last longer than one hour. However, there is no advantage in drinking more than you need – in fact if you do you run the risk of exercise-associated hyponatraemia, an electrolyte imbalance that results when you drink too much fluid. 

To avoid dehydration and hyponatraemia, you need to drink approximately 200-300ml (3-4ml per kg of body weight) every 15-20 minutes. Remember your stomach can only empty 800-1000ml of fluid per hour, and your own requirements may be less than this. 

After the event

Fluid replacement after a bout of serious exercise should aim to fully replace any fluid and electrolyte loss accumulated during exercise. To estimate your own fluid requirements, it’s always good practice to monitor your weight before and after exercise sessions. To get a rough idea, each kilogram of weight lost during a workout is equivalent to approximately one litre of fluid.

Ideally, you need to replace 125-150% of this fluid deficit over the next 2-6 hours. For example, if you lost 1kg (1000ml), you will need to drink 1250-1500ml to fully rehydrate and to account for ongoing fluid loss through sweat and urine.  

Generally, you need to drink approximately 1-1.5litres for every 1kg of total weight loss over several hours.

Bottom line: Everyone is different and there is no one formula that fits all. Remember, preparation is key and it all begins in training to create an individualised hydration plan that takes into account your bodyweight, the intensity and length of the exercise you are doing, and the conditions on the day. Consult an exercise professional for a personalised plan if you need help.

Kathleen Alleaume is an accredited exercise physiologist and nutritionist and founder of The Right Balance