How Much Fluid Should I Drink On The Bike?

 With temperatures starting to rise and the competitive season well underway for many riders, now is a good time to consider your performance nutrition strategies and, in particular, your hydration practices around your key sessions/competitions.

As athletes, our daily fluid needs can vary considerably due to the heightened fluid losses that occur during exercise through sweat. If you’ve ever weighed yourself before and after a hard session, you’ll know that there can be considerable weight loss. Given the general rule of 1kg of weight loss equals roughly 1kg of fluid loss. It’s not unheard of to see losses in excess of a couple of litres per hour, particularly when exercising hard in hot conditions.

Whilst there is a general rule that a 2% loss of body weight (So 1.4kg of loss for a 70kg rider) through dehydration is the threshold beyond which there begins to see a negative impact on endurance performance. This rule is a little oversimplistic.

The impact of dehydration on performance will be influenced by factors like the exercise intensity a rider is riding at and the environment that a rider is riding in. For example, in cooler conditions, where excess heat is less of an issue, a larger fluid deficit can occur before dehydration impacts performance, particularly if a rider is performing at lower exercise intensities. In fact, there is some argument that the weight loss associated with fluid loss can even be performance-enhancing under certain circumstances. In contrast, if a rider is riding at high exercise intensities in very hot conditions, fluid losses less than 2% of body weight may negatively impact performance. A rider’s individual tolerance to dehydration may also play a role here too.

So how much should I actually drink?

Unfortunately, with fluid, due to the huge variability that can occur on a day-to-day basis, in terms of an individual athlete's fluid needs, there is no one-size-fits-all approach. With the dangers of drinking too much, blanket advice can not only be suboptimal for performance, but can be dangerous.

When it comes to fluid intake, we are trying to manage two key things.

1. Drinking enough to prevent dehydration. Or at least prevent us becoming dehydrated enough for it to negatively impact on our performance or our health, which as alluded to, will depend on your individual circumstances.
2. Not drinking too much. Drinking fluid at a rate in excess of our needs can lead to a rider gaining weight and result in fluid overload. This can cause a condition called hyponatremia. This is where the sodium within the blood becomes diluted and results in brain swelling, which can, in extreme circumstances, be fatal.

Finding the balance between the two can be a challenge, and how much to drink is specific to the individual’s circumstances. There are generally two camps for how to approach your hydration strategy.

Drink to thirst – This is as it sounds: where you basically drink, when you’re thirsty. It’s a relatively simple and safe strategy that is unlikely to lead to drinking too much and, therefore, prevent hyponatremia, but it can be problematic in that it can lead to dehydration as a result of the delay in thirst response to fluid losses. It also relies on having a constant availability of fluid which logistically isn’t always the case during rides/competition where it may not be practical to carry large volumes of fluid and there can be large distances between water stops.

 Drinking to a plan—This involves drinking a set amount based on a pre-determined amount of fluid, typically to first prevent drinking too much and second drink enough to prevent fluid losses exceeding amounts likely to negatively impact performance. This approach requires additional work ahead of an event to help an athlete develop an individualised hydration strategy through developing an understanding of their individual fluid needs are likely to be when it comes to the event they are targeting. Drinking on a plane can be a challenge as it may require fluid to be consumed at a rate that may be uncomfortable or requires extensive work pre-race to develop a tolerance.

What about electrolytes?

As we’ve talked about in a couple of previous blogs, due to the hypotonic nature of sweat (i.e. it has less sodium in it than the water component of blood) as we sweat during exercise, the concentration of sodium within the body actually increases and unless we can realistically replace over 70% of our fluid losses, which isn’t always practical due to the stomach issues associated with consuming large volumes of fluid) and are exercise being over 4hours in duration, you can simply add salt to taste. There isn’t an inherint need for it

For more on how to develop your own fuelling and hydration strategy, check out fuel the ride academy.

• Coach Ben