How to start a long swim well hydrated

By Dave Colley | 8 Minute Read

Hydration isn't something that immediately comes to mind when thinking about swimming because drinking isn't something we tend to do when we're actually in the water (unless you're yet to perfect your technique and you're taking in plenty of lovely sea/river water...).

But starting hydrated is crucial to performing at your best during longer swims. 

You might not notice it, but you'll be sweating during the swim and - because you're not usually in a position to replace those fluid/electrolyte losses when you're in the water - it's important to start fully topped up. 

Drinking a strong electrolyte drink before longer swims can significantly improve your performance by boosting your blood plasma volume. ﻿This is often referred to as 'preloading'.

This'll give you a much bigger reserve of fluids and electrolytes to draw upon once you start sweating.

It can also help you avoid cramping up mid/post swim.


What to do

If you want to test whether preloading improves your performance, follow this protocol before your next long swim session or B-race.

Don't just drink tons of water in the build-up to a swim. You'll just end up peeing most of it out and, if you're not careful, you can even end up diluting your blood sodium levels, increasing the risk of a swim-ruining condition called hyponatremia.

Ideally, drink a strong electrolyte drink (like PH 1500, which has 3x more sodium than typical sports drinks) the night before events lasting more than about 90 minutes- 2 hours.

Drink another strong electrolyte drink about 90 mins before you get into the waterDrink the electrolyte supplements in water you’d have drunk anyway to ensure you don’t overdo it.


The science behind 'preloading'

Once you begin sweating you're generally going to be fighting a losing battle against fluid and electrolyte loss, which is why starting off properly hydrated can be extremely beneficial. When you're properly hydrated you have a larger reservoir of fluid to draw from over time than if you're dehydrated.






But it can also be a problem for full-time athletes when training two or more times a day, or at times when they’re just under a very high total training load. That's because uncorrected dehydration from a prior training session can make it’s presence felt when the next session gets underway. This blog addresses how to optimise your recovery by hydrating properly.






I’ve written about the common tendency to over-drink before races in the past and the bottom line is that it's a very real problem that can potentially lead to hyponatremia (i.e. low blood sodium levels caused by inadequately replacing the sodium lost when sweating and further dilution by drinking plain water or weak sports drinks), something that can be pretty catastrophic for health and performance if it goes unchecked.



Carb loading is a no brainer. But, can you do the same with water?

The idea of carb loading - i.e. maximising the amount of glycogen you have stored in your muscles and liver before a strenuous activity - is one that's well researched and essentially universally accepted as a performance-enhancing tactic.

OK, so sports scientists love to argue over exactly what and how much you should eat, and when exactly to shove it in your cake hole, but few sane athletes would argue with the principle that consuming additional carbohydrate calories (often combined with a tapering off in training load) in the final days before an event is a good idea.

That's because you can store up and subsequently use a lot of this energy later on when you need to dig deep and burn through large amounts of fuel during a long or hard effort.

With hydration things are less clear cut than with carbs.  As we've seen, many athletes do tend to increase fluid intake prior to important events or hard training sessions, with the vague notion that having more in the tank should result in better performance. But many unfortunately over do it in the process and this is harming their performance.

But, can you actually store fluid over and above being normally hydrated and, if so, does it help to do so?

The answer has a lot to do with not just how much water you drink, but with how much sodium you consume with that water as it’s this electrolyte that plays a key role in retention of fluid in the body and in the bloodstream in particular. For more on why sodium is crucial to staying hydrated and maintaining your performance, you may want to read this blog.

In a nutshell though, without the right amount of sodium in your pre-exercise drinks, drinking lots of water will do you a fat lot of good. The importance of sodium to hydration and maintaining your performance was further proven by research conducted at NASA at the end of the 20th century.




On top of the work by NASA, there have been a number of scientific studies conducted into the idea of athletes ‘preloading’ with sodium and fluids prior to exercise in the last few years and the key findings from this work were summarised in a paper back in 2013.

This review article essentially came to the same conclusion as NASA that sodium preloading with a drink strong enough to stimulate fluid retention in the blood stream, but not so strong that it caused other knock on issues, does seem to improve endurance performance. 

As I mentioned, a higher blood volume means an easier time for your cardiovascular system when you’re exercising and also a bigger reservoir of fluids available to ‘lose’ through sweating if you need to cool down, as is the case when working your muscles hard and producing lots of metabolic heat.

However, due to the mechanisms that control fluid and electrolyte balance in the body, any attempt to preload with plain water inevitably just leads to more trips to the bathroom as your body tries it’s best to avoid an excessive dilution of your blood sodium levels, which would lead to hyponatremia if unchecked.


What strength drink is right for preloading?








In the end we settled on a strength of 1,500mg/l (32oz) for our preloading drinks and these are available in as all-natural PH 1500 drink mixes as well as low-calorie effervescent tablets.


Enjoy the swim!

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