It’s important to stay hydrated, whether you’re competing for the Olympics or doing some Olympic style shopping however a lot of myths surround hydration and the best way to ensure optimum levels without over drinking. Andy Blow is the founder of Precision Fuel and Hydration and he shares his expertise on how to stay hydrated during times of extreme heat or activity while debunking hydration myths too.
At what severity does hydration affect performance?
The ACSM Guidelines suggest that dehydration of up to 2% body mass loss is acceptable, but dehydration beyond this point is likely to be detrimental to performance and health.
A number of scientific studies have illustrated that too great a level of uncorrected dehydration can impact physical performance to a certain extent.
Some level of fluid loss is acceptable, but defining an exact level of dehydration that negatively affects performance is proving elusive as there is no one-size-fits-all solution to this complex problem and athletes will respond to environmental conditions, intensity and duration of exercise differently.
For example, some can tolerate higher levels of dehydration whilst other athletes cannot. As a result, athletes should always respond to the dictates of thirst and aim to start exercise well hydrated.
Body mass changes (identified using a set of scales) should be used as a measure for estimating sweat losses during exercise. It should be noted that peeing or going to the toilet will influence this data. Within this, one kilogram of body mass loss is said to be equal to one litre of sweat. It seems clear that aiming to replace all of your sweat losses during exercise is unnecessary and challenging for those with higher sweat rates.
The sweet spot is likely to be highly individual and may even be slightly different for the same athlete on different days, in different climates, but generally speaking, dehydration of between 2-4% of body weight loss is said to be the cut off before it becomes detrimental to performance.
Is pre-loading with fluid necessary?
The concept of pre-loading refers to an athlete’s intake of sodium and water prior to a training session or event.
Drinking a strong electrolyte drink of ~1500 milligrams of sodium per litre of water to optimise an athlete’s hydration status before sessions or races, can significantly improve performance.
The consumption of additional sodium with fluids before exercise and the onset of sweating is effective in promoting acute fluid retention and consequently improving performance, particularly in the heat.
By doing this, and starting hydrated, the reservoir of fluid available to draw from is significantly larger than if you are starting dehydrated. This ‘pre-loading’, maximises your blood volume, helping with general cardiovascular function and increasing the body’s ability to dissipate the heat produced by muscles. Consequently, this reduces fatigue and helps maintain performance for extended periods.
Drink to thirst or to a schedule?
There are many scenarios where just drinking water to thirst is sensible (ie., day-to-day hydration). Additionally, for athletes engaging in short training sessions/races in cooler conditions, drinking to thirst is likely sufficient. But this isn’t always the case and will depend on the goals of that session whether that’s health or performance- focused.
There are some issues associated with recommending ‘drinking water to thirst’ to all athletes in all scenarios.
When sweating, fluids lost will increase the concentration of sodium in the body, which increases your drive to drink. Listening to your body and responding with fluids is beneficial, but if you don’t get it quite right, the consequences can be detrimental. For example, when exercising for long periods of time in hotter climates, even if an athlete drinks ‘moderately’, increased rates of fluid and sodium loss will increase the likelihood of hyponatremia.
Whilst most individuals do realise and sense thirst, when racing or training hard, an athlete’s perception of thirst may be blunted or masked by a host of factors, therefore exclusively relying on biofeedback may not support their hydration sufficiently.
With increasing evidence available to suggest that supplementing with electrolytes has a positive effect, it would be naive to suggest that drinking to thirst is always adequate.
Athletes should devise a hydration strategy that is suitable for the environmental conditions, exercise duration, intensity and individual rates of sweat loss, and should be tweaked on the move based on biofeedback and sense of thirst.
Are electrolyte tabs really necessary?
Supplementing with electrolytes in one way or another is highly beneficial for endurance athletes. Sodium, as the major electrolyte found in sweat, plays a key role in the functioning of the human body, by maintaining fluid balance and cognitive function.
It also plays a role in the absorption of nutrients in the gut, nerve transmission and muscle contractions. As sweat (and sodium) losses accrue, blood volume is reduced, which increases the strain on the cardiovascular system, making it harder to pump blood around the body.
Additionally, fatigue and the likelihood of cramping will increase if sodium losses go uncorrected or significant imbalances between fluid and sodium are allowed to occur.
Everyone loses a different amount of sodium in their sweat (and this is largely genetically determined), with some athletes losing more than 2,000mg of sodium per litre of sweat. So, if you’re a salty sweater and you have a high sweat rate, your losses in long, hot races can only be adequately replaced through supplementation.
The source of this sodium supplementation is relatively unimportant (e.g. tablets, drink mixes, capsules) but replacing proportionally to an individual’s losses is key.
Common hydration myths that need to be debunked?
“My urine is clear – I am definitely hydrated!”
This is a common misconception that you are optimally hydrated if your urine is a clear colour. Although the colour of your urine can help you understand how your hydration status fluctuates on a daily basis, drinking fluids until your urine is clear is not the route to optimal hydration.
In some scenarios, athletes find themselves over-drinking to achieve clear urine, which can contribute to hyponatremia (the dilution of the body’s sodium levels). Additionally, there are other factors that can affect the colour of your urine including alcohol, tea, coffee, nerves and medications). In general, it’s more important to pay attention to how you feel rather than solely the colour of your urine.
“You can’t overhydrate.”
As mentioned within this, overhydration or the excessive consumption of fluids can be incredibly dangerous and lead to hyponatremia. More is not better when it comes to hydrating.
“Caffeine dehydrates you.”
Caffeine is widely regarded as a mild diuretic (a compound that causes your kidneys to produce more urine than usual). However, it has been observed that consuming coffee doesn’t actually cause increased fluid losses, when you consider the amount of liquid consumed and retained form the coffee itself. Individual responses to caffeine differ based on the body’s ability to metabolise the stimulant, so the effects may vary depending on your genetic makeup. With this in mind, caffeine shouldn’t be considered as a drink used to rehydrate you and is not the optimal choice. But there’s no evidence suggesting it dehydrates you either.
How to ensure optimum hydration while training/racing?
There is no one-size-fits-all hydration strategy during training and racing, and with varying sweat rates and sweat sodium concentrations, each athlete’s needs are individual. That being said, there are a number of ways to encourage optimal hydration.
For shorter races or training sessions (up to ~90 mins), drinking is not as much of a concern and listening to thirst cues within the session will likely be sufficient to prevent your mouth from drying out. You will lose fluid during the session but should be able to replace this easily post-exercise through ‘normal’ food and drink, and the low level of dehydration you will incur will not be enough to impact performance.
For longer sessions (more than ~90 mins) the need for fluids becomes more apparent and the volume of this is largely driven by an athlete’s sweat rate. As a result of the variability in sweat losses as discussed, a ‘one-size-fits-all’ recommendation on how much to drink is unlikely to work for everyone. Listening to your body and drinking to the early signs of thirst are a good idea but not sufficient. Beyond this, it’s sensible to evaluate your strategy, and drink relative to your losses.
Here are some rough guidelines to go off, but sweat losses should be measured before calculating an intake to limit more than a 2-4% loss of body mass and subsequent dehydration.
In cooler conditions, or where sweat losses are minimal, ~500 millilitres of fluid per hour should be sufficient for most people. In warmer conditions, or scenarios where sweat rates are higher, up to ~750ml/hour could be required. In very hot or humid conditions and/ or when sweat rates are considerably high, you may find you need >1L/hour of fluids. In addition to this, adding sodium to the fluids you are consuming is critical to support performance and prevent the onset of dehydration.
It’s worthwhile for athletes to measure their sweat rate, set some guardrails and then begin experimenting and being flexible depending on the session or race. The intensity, duration, weather conditions and the overall goals of the session will impact sweat rates. In conditions where sweat rates are likely increased (hotter weather, high intensity), sodium replacement should also increase, so it should be advised that athletes experiment with both their fluid and sodium intake to find a balance that best suits them.
For athletes doing longer and/ or hotter training sessions, or those with heavy sweat losses, getting their sweat tested can also be a really useful way to optimise their hydration strategy.
How to avoid overhydration?
A significantly increased fluid intake can lead to an entirely separate set of issues as a result of hyponatremia (low blood sodium levels caused by inadequately replacing the sodium lost when sweating, and further dilution by drinking plain water).
Hyponatremia occurs when the sodium and fluid in the body are out of balance (ie., too much water and/ or not enough sodium). With dramatic shifts in the body’s electrolyte/fluid balance, the body’s cells start rapidly taking in water with the aim to reduce the amount of water in the bloodstream, consequently causing them to swell. An extreme intake of water can be highly detrimental, (intentionally over drinking or even just sipping extra water prior to a race).
With the overconsumption of water, blood sodium levels are diluted, and plasma osmolarity is then decreased. This triggers the body to increase its urine production, flushing both fluid and electrolytes out of your system.
The best way to avoid this would be to measure your sweat rate and drink in relation to this, the environmental conditions and also your sense of thirst. It’s also important to replace an adequate proportion of your sodium losses through sweat using an electrolyte drink or capsules. Frequent urination is a key indicator that you might be drinking too much.
Does hydration cause or contribute to heat stress/exhaustion?
Heat exhaustion is usually identified by symptoms such as headaches, muscular weakness or cramps, and possible vomiting or nausea. Exercise-related heat exhaustion occurs primarily as a result of overheating, due to a limited fluid intake with excessive sweating. Heat stroke is a very serious form of heat-related illness that occurs when core body temperatures rise above 40 degrees Celsius (104 degrees fahrenheit). Individuals who have developed heat stroke actually stop sweating as the body’s thermoregulatory system struggles to function and it cannot cool down.
The risks of these two heat-related illnesses can be mitigated against through acclimation, in which the body adapts to the heat, allowing you to hold a higher work rate at a given temperature. Hydration also plays a key role in avoiding these issues; adequate fluid replacement will maintain plasma volume so that circulation and sweating can continue.
Does hydration need to be adjusted with age?
Ageing results in a number of physiological changes, including the decrease in muscle mass in the body. Muscle cells hold a large proportion of intra-cellular fluid (water locked inside cells) and with a decrease in muscle mass, total body water also declines. Although exercise can help reduce the loss of muscle mass with ageing to an extent, it’s almost impossible to prevent this and so a significant chunk of your fluid ‘reservoir’ is lost with ageing. This directly correlates with dehydration and makes older athletes more susceptible to this.
Additionally, older athletes tend to lose more water through urine. This is as a result of deteriorating kidney function which means that less concentrated urine can be produced and as a result, more free water is lost when you pee. This could also be compounded by a reduction in circulating hormones like aldosterone, which is responsible for helping retain water. So, less aldosterone increases the need to pee, and therefore increases the total water loss from the body.
Finally, ageing lowers your sensation of thirst meaning you want to drink less and consequently are, again, more susceptible to dehydration. The above three factors strongly suggest that older athletes need to be a bit more diligent with their hydration practices with a reduced margin for error and increased risk of dehydration.
It’s recommended for older athletes to pay close attention to both their fluid and sodium intake. By supplementing with sodium at times when your hydration levels may be challenged (e.g. during and after exercise), you can increase the drive to drink, and help your body balance fluids better. Consuming a strong electrolyte drink (~1000-1500 mg/L) will help ensure you stay hydrated during exercise. All that said, each athlete should be treated as an individual, and the biggest difference between younger and older athletes will be the need for a more proactive hydration strategy.
Should hydration be based on sweat rate?
Sweat rate varies considerably between individuals, and is impacted by several factors including ambient temperature, humidity, clothing, genetics and level of heat acclimation. Sweat rate measurements are usually carried out across a number of sessions in a range of conditions to design a hydration strategy.
With such variations in sweat rate (from <0.5 to >2.5 litres per hour), an individual’s hydration needs will vary considerably.
For example, if you are losing 0.5L of sweat per hour in cool conditions, it’s unlikely that you will benefit from drinking much more than to thirst as your net losses are unlikely to be significant.
However, if you are losing more than 1.5L/hour, during prolonged exercise, a more proactive approach to hydration will be important to prevent significant fluid and sodium depletion (and consequent dehydration). A more structured plan based on fluid loss testing will inevitably mitigate your sweat losses and support performance.
Even with sweat rate data, identifying exactly how much to drink isn’t as straightforward as you’d hope. Athletes often assume they need to replace 100% of their sweat losses (ie., if you lose 1kg of sweat, drink 1L of water). Research has since debunked this, and shown that this logic is fundamentally flawed. Measuring sweat rate should be used to get a decent ‘ball-park’ figure for how much sweat you’ll likely lose over a period of time in a given set of conditions at a certain intensity.
This is incredibly helpful in guiding your hydration strategy but it is also important to defer to your body’s signals to make adjustments in real time, ultimately aiming to limit dehydration to <4% body weight loss.
