Hydrate and make sure you achieve peak sporting performance

Hydrate or die - science in sport

Johanna Shiu continues to look at fitness and performance, this month she considers a vital topic, hyrdation. With so many people training for stand up paddle distance races, taking part in a race or even just out for a recreational paddle hydration is an important topic to understand.

The Hows and Whys of Hydration

Unfortunately, summing up briefly the ins and outs of hydration during SUPing isn’t easy, but do read on, as the knowledge could make or break your performance.

The issue of how hydration affects sporting performance is pretty well covered these days, so you may already know the following:

  • You’re generally considered “dehydrated” after a fluid loss of 1 percent of body weight (eg, 750ml for a 75kg [165lb] person)]
  • You don’t just sweat water, you also lose electrolytes (things such as sodium, potassium and calcium that regulate all sorts of processes in the body, including muscle contraction)
  • With dehydration, the body’s blood volume decreases, there is an imbalance in electrolytes and the ability to get rid of the heat generated by the body is impaired
  • As body temperature increases, heart rate goes up, your body relies more on carbohydrate as a fuel rather than fat, and exercise feels harder
  • The increase in body temperature increases your chances of getting heat cramps, heat exhaustion or heat stroke
  • Even when exercising in the cold, dehydration can still occur

Doing the maths

Sweating is good! We need to do it to get rid of the heat generated as a by product of burning up fuel to exercise. But, for every percent of body weight lost in sweat, performance can decline by around 2 percent. Generally, above 2 percent of body weight can make body temperature and heart rate go up. Above 4 percent loss of fluid, physical performance can be seriously impaired.

In hot and strenuous conditions, it’s possible to lose up to about 1.5 litres of sweat every hour. So, for the 75kg athlete, 2 hours of exercise might mean a fluid loss of 3kg, representing 4 percent loss of body weight. This potentially means an 8 percent drop in performance.

What affects how much you sweat?

Lots of things, including

  • The air temperature
  • How long you exercise for
  • How hard you’re exercising
  • How big you are (the more body area you have, the more you will sweat!)
  • How fit you are (contrary to popular belief – the fitter you get, the MORE you tend to sweat. The body gets conditioned to using sweating as a way to cool down)
  • What you’re wearing – you’ll probably get more hot inside a “dry” wetsuit than a wet one, but be able to sweat less in the dry one (dunk yourself in the sea before you set off)
  • Other environmental conditions: high humidity = less ability to evaporate sweat, so body keeps producing more but is unable to cool down; strong wind = sweat evaporated away from the body more easily

How to get fluid into you

Fluid first of all enters your stomach when you drink it, from where it passes down into the intestines (gastric emptying) and from there, is “pulled” across into the body to hydrate you. All sorts of factors, many of which are complicated to explain, affect how quickly gastric emptying and how rapidly absorption of fluid from the intestines can occur.

Plain water is not particularly well absorbed from the intestines across into the body. Putting electrolytes into the fluid helps the water get dragged across the intestinal wall into the body.

Putting carbohydrate into drinks can also help fluid move from the intestines into the body, but on the flip side, it slows the rate at which fluid leaves the stomach and enters the intestines.

Keeping hydrated

Before exercise
It’s tempting to tactically dehydrate to avoid the need for the call of nature while out SUPing, however, do this at your peril!! You know now how much dehydration can affect your performance and potentially your health.

First of all, make sure that you are well hydrated before you start out on your training or race. Ideally, have your last big drink about an hour before the start of the event, then take regular swigs of fluid for the time leading up to it, having about 200ml 15-20 minutes before (as reference, a standard drink can is 330ml). Having a full “tank” of fluid inside the body is the most effective way to make your body absorbs the fluid you then drink.

What you drink at this time should prioritise getting fluid into you, so could be as simple as plain water, but could also contain some electrolytes to maximise the amount of fluid that is actually absorbed into the body. It could also contain a low carbohydrate concentration to help with keeping your energy levels topped up, if this is a priority to you. Drinks that contain little or no carbohydrate are called hypotonic.

During exercise
The general consensus is that fluid intake should match fluid loss to maintain performance and that this can be achieved by including carbohydrate and electrolytes in the drinks consumed. SUPers are quite lucky, as taking on fluid while paddling isn’t uncomfortable on the guts or difficult to achieve compared to some sports (eg, marathon running or long-distance swimming), so there’s no excuse not to do it.

DO NOT take on sports drinks that you’ve never tried before during a competition. A horrible flavour can be a shock and make you feel sick or not want to drink it, but at worst, a carbohydrate/electrolyte concentration that you’re not used to can give you gut ache and diarrhoea!

If your SUP session is less than about 30-45 minutes and you’re not competing, you can probably get away with not taking on any fluid, but over this amount of time and definitely if it’s hot weather, you need to take drinks with you.

For exercise under an hour, your drink doesn’t need to contain carbohydrate, as you shouldn’t need to take on energy for this duration. However, having some electrolytes in the drink will help you to absorb it and you may decide that a low concentration of carbohydrate will help to make the drink palatable.

For medium-length/medium-distance exercise, your drink may need to meet the twin aims of replacing electrolytes and fluid, as well as providing some carbohydrate. In this case, you will want to have an isotonic drink. This should have a carbohydrate concentration of around 5 to 7%. There is a wide array of sports drinks available to buy that will meet your requirements.

If you’re considering a long-distance race, eg a 20 miler, this may take more like 4 to 5 hours. Fluid will be critical to your ability to complete let alone compete, but you may also need to be using your drink to replace lost energy stores. In this case, you have to trade off a little the speed at which you can absorb the fluid and up the carbohydrate content to a more hypertonic solution (between 8-20% carbohydrate). Some manufacturers include glucose polymers in hypertonic drinks. Research is variable, but use of polymers rather than free glucose can make the drinks more pleasant to drink, and can also help to increase their rate of absorption.

There’s now good evidence to suggest that some protein can also be useful (see Probing into proteinHow much protein?). ED: Along with some other stand up paddlers I have been using Science in Sport PSP22 and Rego, from my days as a distance runner and cyclist I know these guys produce excellent pre and post session products. Check them out.

Science in Sport PSP22 and Rego

Whatever drink you choose to have, try to take three to four sips of it every 10 minutes. This is the way to keep your fluid “tank” topped up and to maximise the rate of gastric emptying.


  • If replacing fluid is your priority – include electrolytes, but keep the carbohydrate content negligible to low
  • If replacing carbohydrate is important – up the carbohydrate level, but recognise that this decreases the rate at which water becomes available.

Rehydrating after exercise
Don’t just stop drinking once you’ve finished your training or competition…particularly if you’re intending to do another session later. Get drinking.

To replace lost fluids, you need to ideally drink approximately 1.5 times the amount of fluid you lost. Get to know how much fluid you lose by weighing yourself before and after a training session. Obviously, weigh yourself in the same DRY clothes or in the nude immediately before and immediately after your SUPing, then ADD on to any weight difference the weight of fluid that you drank during the session and that will tell you how much fluid you lost.

weight before = 72.5 kg
drink during SUPing = 1.2 litres (=1.2kg)
weight after = 71.2 kg

Total weight loss = (72.5-71.2)+1.2 = 2.5kg

If you’ve had a hard session and know you’ve lost a lot of fluids, then a suitable rehydration drink will include electrolytes to a) help the water get absorbed and b) replace the electrolytes you’ve sweated out. A low concentration of carbohydrate will also help with the fluid absorption and can help to replenish energy stores if you’re competing again either that day or the next.

Good news – low alcohol drinks can be part of a rehydration strategy!!! Up to around 2% alcohol will not affect your body’s ability to absorb the fluid you’ll be pleased to hear….however, not recommended if you’re competing again or driving home! Once you’re up to 4% alcohol, this slows down the rate at which you can rehydrate (but maybe you won’t care?!). 

Carrying fluids

Most people find camelpak-type setups the easiest way to take a decent volume of liquid with you, or there are good waistbelts out there for carrying drinks. Many SUPs now have cargo net-type storage or water bottle holders on them, although having to reach down for bottles etc can be fiddly and too much of an interruption to your paddling. Work out how you will carry your fluids and how much to carry BEFORE your race. Make sure any drink bladder valves/drink bottle necks etc are functioning properly and consider taking spare fluid on board rather than just the amount you calculate you need for your race if it’s a long distance one. It’s better to come back with spare drinks rather than come back dehydrated.

How to tell if you’re hydrated

Quite simply, get used to studying your pee! If you’re well hydrated, you should have very pale yellow urine that has little odour to it, and be producing a reasonable volume (ie, not just going twice per day!). As you get dehydrated, urine will become darker yellow, take on a stronger smell and the volume produced will get less and less. If it’s greenish or brownish, this is not good (and trust me, working with boxers previously, I’ve seen some this colour!)

However, bear in mind that some supplements and food items, definitely beetroot, can alter the colour of your pee. I’ve known at least three people now who have thought that they were seriously ill or dying, but in fact, they’d just eaten a lot of beetroot the night before!! Also, both asparagus and some supplements can change the smell of your urine.

If you don’t want to have to study your urine so much, keep drinking!!!

It’s worth bearing in mind that feeling thirsty is NOT a good indicator of how well hydrated you are. Generally, if you feel thirsty, you are probably already dehydrated.

Also, if you’ve got yourself dehydrated, depending on what you drink (ie, whether you have plain water or if you take on a properly-formulated sports drink), it will take up to 30 minutes to regain your full performance capacity.

And lastly…can you drink too much?

In short, yes, and this can lead to hyponatraemia. This condition, which is sometimes also referred to as water intoxication, means that you have a low sodium concentration in the body, which can interfere with how nerve impulses are transmitted and the way in which muscle contracts.

Hyponatraemia can be caused as a result of heavy sweating and drinking copious volumes of plain water. The problem is becoming increasingly common as more novices enter endurance events, particularly with conditions in which sweating is profuse…eg, a hot, long SUP race.

Unfortunately, the early warning signs of this may be similar to dehydration, including muscle cramps, nausea, disorientation, slurred speech and confusion, so people drink more water, believing that they are helping. However, drinking plain water without any sodium in it will increase the problem of hyponatraemia. At the most extreme, someone with this problem may experience seizures, coma or death. This is avoided by drinking fluids that include sodium or eating salty foods along with drinking water.