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The Effects of Hydration on Athletic Performance & Hydration Strategies for Athletes

What is Hydration?

Hydration refers to the process of maintaining an adequate balance of fluids in the body. Hydration status has three main conditions in science, referred to as hypohydration, euhydration and hyperhydration, each of which are outcomes and defined in the table below. We therefore define dehydration as a process of moving from hyperhydration or euhydration, to hypohydration. 


Hypohydration

This condition occurs when there is a deficit of body water, leading to potential impairment in physical and cognitive performance.

Euhydration

This is the state of normal body water content where the body's fluid balance is optimal for physiological function.

Hyperhydration

This state happens when there is an excess of body water, which can dilute electrolytes and potentially lead to conditions like hyponatremia.


Water makes up 50-70% of the human body, with a fundamental role in numerous physiological functions. It is distributed between intracellular (65% inside cells) and extracellular (35% outside cells). The water content of various tissues and organs varies considerably, with fat containing roughly 10% water and muscle up to 75% water. With water making up such a large proportion of body mass, it’s often an obvious target for athletes needing to lose weight rapidly, equally fluctuating body fluid can cause mass confusion and frustration among serial dieters. 

Water is essential to life, and adequate hydration is required for the body to function properly; it supports cellular processes, regulates temperature, and facilitates the transport of nutrients and waste. Dehydration, even at mild levels, can have significant negative impacts on health and performance. Physically, it can lead to fatigue and impaired coordination, whilst mentally, it can result in cognitive decline, reduced concentration, and mood disturbances. Ensuring sufficient fluid intake is vital for maintaining optimal health, physical endurance and mental clarity, whilst preventing the adverse effects of dehydration.

Dehydration is caused when our fluid balance in the body is inadequate. It is constantly changing, as we lose water through urine, sweat, skin loss, expired air and faeces. The rates of this water loss can change dramatically from person to person, and within different environmental conditions. We obtain water through fluids, food and metabolic water (Jequier & Constant, 2010).

Exercise is the main challenge to maintaining hydration and fluid balance, particularly in hot and humid environments. Even a small reduction in the body’s water levels, around 2% of body weight (1.6 kg for an 80 kg individual), can lead to noticeable declines in both mental and physical performance. Euhydration is generally well maintained by behavioural and biological controls, such as thirst. Generally, even small fluid losses of 1% loss of body mass are compensated for within 24 hours as a result of the body’s intricate regulatory mechanisms (Jequier & Constant, 2010). However even thirst is not reliable enough to maintain hydration during prolonged exercise (Kenefick, 2018). The balance of body fluids is essential for maintaining peak performance and overall health.


How does the body process water?

When we drink water, the body absorbs it primarily through the gastrointestinal tract. The process actually begins in the mouth, where small amounts are absorbed, but most absorption occurs in the small intestine. Once in the small intestine, water passes through the intestinal walls into the bloodstream via osmosis, a process driven by the concentration gradients of electrolytes and other solutes which we will discuss in more detail later. From the bloodstream, water is distributed to cells and tissues throughout the body, where it performs various functions such as maintaining cell structure, facilitating biochemical reactions, and regulating body temperature.

The Role of the Kidneys in Hydration

The kidneys play a crucial role in managing water balance by filtering blood, reabsorbing needed water, and excreting excess water and waste products as urine. This regulation ensures that the body's hydration levels remain stable. It is managed by hormones such as vasopressin and antidiuretic hormone. These neuroendocrine responses help to regulate fluid balance by driving biological reactions such as thirst stimulation and urine output. Research has indicated that vasopressin is elevated when we consume less than 1.8 litres per 24 hours; this signals the body’s need to conserve water by reducing urine output. On the other hand, drinking large volumes of water in a short period reduces vasopressin leading to increased urine output (Armstrong & Johnson, 2018). 

Water Storage & Retention

The body does not store water in the same way it stores fat or glycogen. Instead, it maintains a balance through continuous intake and excretion. Factors such as physical activity, environmental conditions, and dietary intake can impact water balance. For instance, increased physical activity or hot weather can lead to greater water loss through sweat, necessitating higher fluid intake to maintain proper hydration. Conversely, a high-sodium diet can cause the body to retain more water to help maintain electrolyte balance. Thus, regular and adequate fluid consumption is essential to support the body's water needs.

Other than its impact on physical health and performance, we also know that fluid balance can impact metabolic processes and even weight management (Roumelioti et al., 2018). Some research has suggested that increasing fluid intake can promote weight loss and improve body composition through thermogenesis (Vij & Joshi, 2013) or increased fat burning (Thornton, 2016).

The Role of Sweating during Exercise

Sweating is a bodily process which plays a key role in thermoregulation during exercise by dissipating heat through evaporation, which helps to maintain core body temperature. Roughly 75% of the energy produced by muscle contraction is heat, so these thermoregulatory mechanisms are absolutely critical (Wendt et al., 2007). However, in hot and humid environments this heat exchange is difficult, so core temperature remains elevated and performance can suffer significantly. Performance in the heat can decline by as much as 30%, primarily due to hyperthermia-induced changes to cardiovascular, central nervous system and muscle function alterations (Periard et al., 2021).

Excessive sweating can lead to significant fluid and electrolyte losses, negatively impacting hydration status and potentially impairing performance and health (Sawka et al., 2007). Roughly 99% of sweat is water, although sweat also contains electrolytes, including sodium, chloride, potassium, calcium, and magnesium. The composition of sweat can vary significantly from one individual to another due to factors such as genetics, diet, acclimatisation to heat, fitness level, and hydration status (Baker, 2017). Some people may lose more sodium in their sweat, while others may have higher concentrations of other electrolytes. This variability shows the importance of personalised hydration strategies, especially for elite athletes, which we will discuss in more detail later in this article.

How do you Measure Hydration Status?

The interesting thing about hydration is that there is currently no single method of assessing hydration status that is entirely reliable. Instead, a combination of methods can be employed for a greater degree of accuracy. Methods can range from invasive techniques like neutron activation analysis to non-invasive ones like observing urine colour and body mass. It should be noted though that salivary and urine assessments, while convenient, lack general accuracy in measuring hydration.

Currently, the best and most practical measure of hydration status is a combined assessment of body mass change and urine concentration (specific gravity or osmolality and colour) (Barley et al., 2020). In a practical sense for amateur athletes, monitoring body mass each morning and assessing urine colour and thirst throughout the day can be considered an okay measure. Also assessing body mass before and after training sessions is important to evaluate hydration level at these times; pre-training as hydration is key for performance, and post-training as hydration is required for optimising recovery.

The Impact of Dehydration on Athletic Performance

Dehydration presents a range of symptoms depending on its severity. Mild to moderate dehydration includes signs like thirst, dry mouth, reduced urine output, dark urine colour, dry skin, headache, dizziness, and fatigue. In a sporting context, dehydration can negatively impact performance, increase the risk of muscle cramps, increase muscle damage and pain perception, and prolong recovery. Severe dehydration is more critical and includes extreme thirst, very dry skin, lack of sweating, rapid heartbeat, sunken eyes, low blood pressure, confusion, and fainting. Severe dehydration requires immediate medical attention to prevent serious health complications.

In sports settings, an athlete is generally considered dehydrated when they lose more than 2% of their body weight due to fluid loss. So if an 80 kg individual were to lose 1.6 kg through sweat then this would be considered dehydrated. This level of dehydration can impair physical performance, cognitive function, and thermoregulation. Dehydration obviously exists on a continuum of severity, with coma and death becoming a real risk at >10% body mass loss. 


Why is Hydration Important in Sports?

Impact on Cognition & Perceived Exertion

As we have discussed, dehydration can negatively impact metabolism, cells, tissues and organs significantly, none more so than the brain. Although generally speaking, mild dehydration of around 2% body mass loss does not critically impair cognitive function, including complex attention, executive function, learning, and memory (Goodman et al., 2019). One meta-analysis has demonstrated that more severe dehydration, of 3-5% body mass loss resulted in significantly impaired cognitive performance. Symptoms included mood disturbances, fatigue, and increased perceived exertion (Dube et al., 2022). Mood has been consistently shown to be affected by even mild dehydration, which is an important factor to consider in day-to-day life. 

Dehydration can make exercise feel more difficult, as measured by the rating of perceived exertion index. A meta-analysis of 16 studies with 147 participants demonstrated that dehydration (with a body mass loss of 1.7-3.1%) increased RPE by 0.21 points for each 1% increase in dehydration. Notably, significant increases in perceived exertion are observed at body mass losses of 2.3 ± 0.5%, with a maximum difference of 0.81 points in RPE between hydrated and dehydrated states (Deshayes et al., 2022). On the topic of perception, research has also shown that dehydration can increase the perception of pain by as much as 44%, which is not beneficial during hard training or competition (Cleary et al., 2005). 

Another interesting thing about dehydration is that even being told you are dehydrated can negatively affect performance. Funnell et al., (2024) reported a 5.6% reduction in performance when participants believed they were dehydrated, despite actual hydration status being the same as those who were told they were hydrated. Another study led by James et al., (2017) found that hypohydration led to an 8% reduction in physical output compared to when they were well hydrated, despite the participants being blind to whether or not they were being provided with water (fluids were delivered through a nasal tube). These studies ultimately demonstrate that hypohydration can negatively impact performance through both physiological and perceptual or psychological mechanisms. 


Impact on Cardiovascular Function and Aerobic Performance

The cardiovascular system is also significantly impacted by dehydration. Research has shown that for every 1% loss in body mass due to dehydration, heart rate increases by an average of 3 beats per minute (b·min⁻¹). This increase in HR is consistent across various exercise intensities and highlights the additional cardiovascular strain dehydration imposes (Adams et al., 2014). This is an important consideration for those who assess heart rate and other physiological parameters during training. 

With regards to the practical consequences of these changes to cardiovascular function, research has demonstrated that runners who complete a 3 km time trial on a treadmill were 6% slower than when they completed the same time trial in the hydrated state (Funnell et al., 2023). Both 5 km and 10 km running performance is also impaired by hypohydration, with 6.7% and 6.3% slower run times respectively (Armstrong et al., 1985). 

Similarly, a meta-analysis concluded that hypohydration, with an average body mass loss of 3.6%, decreases aerobic exercise performance by 2.4%, peak oxygen consumption by 2.4%, and oxygen consumption at lactate threshold by 4.4% (Deshayes et al., 2020). In cycling, another meta-analysis found that fluid consumption to maintain hydration status improves performance during moderate-intensity cycling (>1 to ≤2 hours) by 2.1% and during long-duration cycling (>2 hours) by 3.2%. 

Conversely, during high-intensity, short-duration (1-hour) cycling, fluid intake can impair performance by 2.5% (Holland et al., 2017). This suggests that in certain contexts where optimising the power-to-weight ratio can be of benefit to sport performance, such as sprint cycling, reducing body mass slightly through dehydration might actually be advantageous. This is perhaps specific to sprint cycling, as research has shown that sprint speeds are slower when dehydrated (Baker et al., 2007; Davis et al., 2015; Gamage et al., 2016)  


Impact on Muscular Function, Glycogen Breakdown, and Technical Skill in Sport

Muscle is roughly 75% water, so it is no surprise that muscle function is impacted by dehydration. A meta-analysis confirmed that hypohydration significantly reduces muscle endurance by 8.3%, muscle strength by 5.5%, and anaerobic power by 5.8%. Anaerobic capacity and vertical jump height are impacted to a lesser extent, with only a 3.5% decrease (Savoie et al., 2015). 

Interestingly we also know that dehydration can accelerate the rate of glycogen breakdown during intense exercise, so you are more likely to fatigue earlier and also prolong the time it takes for glycogen to be restored after exercise, meaning recovery takes much longer. This will certainly have a negative impact on prolonged and repeated high-intensity sports such as Hyrox and team sports (Lopez-Torres et al., 2023).

Research has also indicated that dehydration can negatively affect technical performance and sport-specific skills. In basketball, dehydration has been reported to reduce shooting accuracy, and impair reaction time and vigilance (Baker et al., 2007; Hoffman et al., 2012). In football, dribbling, reaction times and memory are all negatively impacted (McGregor et al., 1999; Bandelow et al., 2010). In hockey, decision-making (MacLeod & Sunderland, 2012) and in cricket, bowling performance are all impaired when athletes are dehydrated (Devlin et al., 2001).  

Hydration for Athletes

Research suggests that up to 71% of adults consume less than the current fluid intake recommendations (Armstrong & Johnson, 2018). There is also research to suggest that up to 56% of professional athletes (Chapelle et al., 2020) and approximately 70% of collegiate athletes are dehydrated before practice, indicating a gap between guidelines and actual practice (Kostelnik & Valiant, 2023). So, dehydration is a real concern affecting many people. 

The current gold standard recommendation for fluid intake is approximately 1 ml of water per kcal of energy expenditure under average conditions, increasing to 1.5 ml/kcal to account for variations in activity and environment. This equates to about 2.5 to 3.7 litres per day for men and 2 to 2.7 litres per day for women. Factors such as age, climate, and physical activity significantly influence these requirements of course (National Research Council, 1989).

Athletes specifically are recommended to calculate individual sweat rate during training prior to competition and consume sufficient fluids to offset that loss through sweat, limiting dehydration to less than 2% body mass loss to prevent performance impairments. As previously discussed, sweat rates and sweat composition vary widely among athletes, ranging from 0.5 to 3.0 L/hr, and fluid needs can increase by 1 to 6 L/day during intensive training. High-risk events like long-distance running and walking require more meticulous hydration strategies, including personalised fluid intake plans and electrolyte replacement (Casa et al., 2019). 

Sweat rate is relatively easy to calculate, using the below formula. An online sweat rate calculator has been developed by Jay et al., (2024) and the prediction model displays high accuracy, with mean absolute errors of 0.03 L/hr for running and 0.02 L/hr for cycling.

As we touched on earlier, sweat is not purely water, so it is important to also consider replacing the electrolytes, particularly the sodium element, lost in sweat, especially during prolonged exercise in hot environments. The composition of sweat varies considerably, with intraindividual (day-to day) variability of around 5 - 7% and also significant regional variability across different locations on the body of 80 - 120%. 

Interindividual variance has been reported from anywhere from 10 mmol to 90 mmol/L of sweat (Baker, 2017). Endurance athletes have been reported to lose around 43 ± 8 mmol/L of sweat or 1546 mg of sodium per hour (Rivera-Brown & Quinones-Gonzalez, 2020). Thankfully the assessment of sweat sodium composition is becoming more accessible and practical, and equally valid and reliable, thanks to wearable tech such as Flowbio. The function of sodium and consequences of significant sodium losses have been discussed at length in our other blog post, but here we will discuss the importance of sodium relative to hydration status and fluid balance. 

Studies have consistently demonstrated that drinks with a higher sodium content improve fluid retention compared to lower sodium levels (Millard-Stafford et al., 2021). In fact, pre-exercise sodium loading has been reported to be more effective than hyperhydration with glycerol and water at increasing plasma volume (Perez-Castillo et al., 2023). Drinks with a higher sodium content result in a 36% greater rehydration rate than those with no sodium (Ly et al., 2023). Drinks with a higher sodium content also result in increased voluntary fluid intake compared to plain water, through an increased thirst drive. Specifically, higher sodium concentrations resulted in a 29% increase in fluid consumption, enhancing rehydration efficiency and reducing the risk of dehydration after exercise (Wemple et al., 1997). Further research has shown that high-sodium drinks significantly reduce urine output compared to low-sodium drinks, with a 40% improvement in fluid retention (Jones et al., 2010). Be sure to take a look at our hydration drinks, which contain 500mg of sodium. 

Athlete Hydration Strategies

General recommendations for daily fluid intake were provided earlier in this post. More specific recommendations for fluid intake to maintain hydration and performance in athletes prior to, during and after exercise have been researched for many years now. The current consensus suggests that consuming 5-10 millilitres of fluid per kilogram of body weight 2 - 4 hours before exercise is sufficient to achieve euhydration in most athletes (Kostelnik & Valiant, 2023). Additional recommendations for fluid intake during and post-exercise have also been summarised in the table below (Casa et al., 2000). 


Time

Recommendation

Practical example for 80 kg athlete

Before exercise

Athletes should consume 5 - 10 mL per kg body mass 2 - 4 hours before exercise and an additional 200 - 300 mL (7-10 fl oz) 10 - 20 minutes before exercise.

400 - 800 ml of fluid with additional sodium 2 - 4 hours pre-exercise and 200 - 300 ml 10 - 20 minutes pre-exercise.

During exercise

Fluid intake should approximate sweat and urine losses, typically 200 - 300 mL (7-10 fl oz) every 10 - 20 minutes.

Calculate sweat rate and sweat sodium composition to meet unique requirements.

High intensity events greater than 70-minutes will require additional carbohydrate (Colombani et al., 2013).

Post exercise

Rehydration should aim to replace 150% of weight loss to account for ongoing fluid losses, ideally completed within 2 hours.

Assuming 1.6 kg weight loss

Consume 2.4 L of fluids with additional sodium within 2 hours of finishing.

 

The above recommendations do not provide any suggestions on the type or composition of fluids required to optimise hydration status and performance at each stage, but that will be covered at length within this post. Ultimately the current evidence suggests that a personalised approach to hydration is necessary to start exercise in a euhydrated state, prevent excessive dehydration (losses greater than 2-3% body mass), and replenish fluids post-exercise. Fluid needs vary based on individual sweat rates, exercise intensity, duration, and environmental conditions. Monitoring body mass changes day-to-day, before and after training, alongside observing urine colour, and thirst can help track hydration status (Belval et al., 2019). 

The optimal composition of electrolyte drinks to improve hydration before, during and after exercise has been studied for many years. The existing evidence suggests that drinks with higher sodium are most effective, through improved fluid retention and plasma volume maintenance (Perez-Castillo et al., 2023). Further research has supported that conclusion with higher sodium drinks leading to greater positive sodium and fluid balance, and reduced urine output (Shirreffs & Maughan, 1998; Maughan & Leiper, 1995). The reported reduction in urine output with higher sodium drinks is around 60% when compared to drinking water only (Merson et al., 2008). Adding sodium to rehydration beverages can significantly improve fluid balance. Specifically, rehydration within a 30-minute period post-exercise has been observed to be around 70% with sodium drinks, compared to only 50% with water (Maughan et al., 1994).

Many individuals choose to train first thing in the morning, with very little time between waking up and commencing a session. A study published by Logan-Springer & Spriet (2013) concluded that it’s possible to rehydrate in just 45 minutes with a high-sodium drink. 

During exercise carbohydrate-electrolyte sports drinks are often encouraged to optimise both hydration and performance. However, the existing evidence suggests that these carbohydrate-sports drinks are only beneficial when exercise exceeds 70 minutes at a high intensity assuming you are exercising in a non-fasted state (Colombani et al., 2013). If hydration during exercise is the only objective, then a sodium-rich drink is equally as effective (Schleh & Dumke, 2018).

Dehydration significantly increases the risk of muscle cramps both during and after exercise. The exact cause of exercise-induced muscle cramps has been and still is widely debated in the research. It would appear that every muscle cramp is unique and perhaps related to different factors. That said, cramps are commonly associated with neuromuscular fatigue, dehydration of greater than 2% body mass, and electrolyte imbalances, particularly deficits in sodium, potassium, and magnesium. Altered neuromuscular control from increased excitatory activity of muscle spindles and decreased inhibitory activity of Golgi tendon organs has been recently reported as a prime candidate (Maughan & Shirreffs, 2019). Maintaining hydration status and electrolyte balance reduces the risk of cramps. Research has shown that individuals who consume water only during prolonged, intense exercise and also have high sweat rates have a 50% increase in the risk of experiencing muscle cramps (Lau et al., 2021). This underlines the fact that water is not enough. 

Drinking only water during prolonged, intense exercise not only increases the risk of cramps but hyponatremia too. Hyponatremia is a potentially fatal condition where sodium levels in the blood drop below 135 mmol/L due to excessive fluid intake or inappropriate antidiuretic hormone (ADH) secretion during prolonged physical activity. Endurance athletes, particularly women and inexperienced athletes are at greatest risk. As much as 30% of ultra-endurance athletes may experience hyponatremia to some degree during competition. The causes include overconsumption of water only during exercise with high sweat rates. In mild cases, hyponatremia can present as nausea, headache and confusion, but in severe cases can lead to cerebral edema, seizure and cardiac arrest. Prevention strategies are clear, consume electrolyte-rich drinks in place of plain water, educate athletes and monitor fluid intake, sweat rate and environmental conditions (Hew-Butler et al., 2017).


How to Rehydrate Quickly Post Exercise

Post-exercise studies have found that consuming a fluid volume equivalent to 150-200% of body mass lost during exercise significantly improves rehydration effectiveness. Again drinks with higher sodium content reduce urine output and improve fluid retention compared to those with lower sodium content. Optimal rehydration requires not only sufficient fluid volume but also an adequate sodium concentration to maximise fluid retention (Shirreffs et al., 1996) and minimise urine losses by as much as 50% compared with water (Ray et al., 1985). Higher fluid volumes (150%) significantly increase urine production compared to lower volumes (100%), suggesting that while larger fluid intake improves rehydration, it also accelerates fluid loss via urine (Mitchell et al., 1994). 

Drinks with higher sodium content are actively encouraged post-exercise as they have been shown to consistently improve hydration status (Gonzalez-Alonso et al., 1992). Higher sodium drinks have been shown to lead to a 2% increase in blood volume and significantly better maintenance of serum sodium levels, demonstrating the critical role of sodium in optimising rehydration after exercise-induced dehydration (Peden et al., 2023). 

Optimising post-exercise rehydration strategies is also of great benefit if exercising again later that same day. With significantly improved performance in a subsequent exercise bout when individuals consumed a high-sodium drink of up to 1.55 L per kg of body mass lost (McCartney et al., 2017). It is also likely that fluid is consumed with food in this recovery period. Research suggests that a high sodium solution leads to greater fluid retention (70%) compared to water (50%) alone, particularly when consumed with a meal (Evans et al., 2017).

Furthermore, it has been reported that dehydration can exacerbate exercise-induced muscle damage and prolong recovery. Likely a result of alterations in cell volume, ion flux, membrane disruption, impaired muscle contraction, reduced blood flow, and increased reactive oxygen species (ROS) production (King & Baker, 2020). Dehydrated individuals reported significantly higher levels of muscle soreness and reduced functional capacity, with a 20% reduction in quadriceps isometric strength at 0.5 hours and a 10.5% reduction at 24 hours post-exercise (Cleary et al., 2005). There is some evidence that dehydration may also impair glycogen synthesis and your ability to refuel rapidly post-exercise (Lopez-Torres et al., 2023), although this has been debated (Burke et al., 2017).

Conclusion

The optimal hydration strategy for you depends on a variety of factors. A personalised approach is recommended. That requires calculation, assessment and a degree of trial and error in practice. This article provides you with all the information you require to develop that personalised, optimal hydration strategy and also confirms that the sodium content within Cadence is optimal prior to and following exercise. 

Interestingly, research has also confirmed that the carbonation of a drink has no impact on its ability to hydrate (Lambert et al., 1992) nor does the beverage temperature. In fact performance improvements of up to 10% have been observed in studies involving cold beverages compared to warmer ones (Burdon et al., 2024). So you can comfortably enjoy an ice-cold Cadence™ Electrolyte Drink prior to and after training to optimise your hydration. 


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