Should You Hyperhydrate Before a Race?

Performance nutrition coach Scott Tindal weighs the pros and cons of hyperhydration (also known as “water loading”) before a race or big training day.

Photo: Johnny Zhang

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Triathlons are among the most grueling endurance events, demanding peak physical and mental performance from athletes. Given the challenging nature of these competitions, athletes are constantly seeking ways to enhance their performance. One aspect that could be useful in targeting is the risk of dehydration and fatigue.

One strategy that has gained attention is hyperhydration, or intentionally over-hydrating before an event. A systematic review titled “The Effect of Pre-Exercise Hyperhydration on Exercise Performance, Physiological Outcomes, and Gastrointestinal Symptoms” delves into the research investigating this practice and provides insights into its pros and cons.

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What is hyperhydration?

Hyperhydration, often called “water loading” or “fluid loading,” is when athletes intentionally consume a larger volume of fluid before an event to enhance their total body water beyond normal levels. This approach aims to create a small fluid surplus within the body, effectively increasing an athlete’s fluid reserves before engaging in intense physical activity – such as a triathlon.

The concept behind hyperhydration is grounded in the belief that having a surplus of fluids can provide advantages in endurance performance, thermoregulation, and overall physiological well-being during the event. It is a valuable strategy when fluid losses cannot be compensated by fluid intake during exercise. It is important to note that water alone is not helpful in hyperhydrating. The use of sodium or glycerol has been investigated to improve total body water in athletes because of their osmotic capacity to induce water storage.

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Why do some athletes hyperhydrate?

Hyperhydration running cycling triathlon
Hyperhydration is one way athletes attempt to prevent or minimize the effects of dehydration before a big workout or race. (Photo: Getty Images)

Preventing dehydration

Dehydration concerns many athletes, especially during endurance events where fluid loss through sweat can be substantial. Hyperhydration is a preemptive measure to counteract fluid losses during the event, potentially reducing the risk of dehydration-related performance declines.


Adequate hydration helps regulate body temperature, a critical factor in endurance sports. Dehydration can result in vasoconstriction of blood to the skin to assist your cardiac function. In doing so, one of your main mechanisms of cooling is reduced. Hyperhydration could offset this by ensuring enough blood volume in your system to keep the heart working efficiently and reduce vasoconstriction. It has also been hypothesized that hyperhydration assists with central cooling. Every one-percent body weight loss results in an increase of core temperature by ~0.15-0.25C. This is one mechanism of how heat stress impacts the body and performance.

Endurance performance

Some studies suggest maintaining optimal hydration levels can positively influence endurance performance. This is related to the negative influence that reduced blood volume from dehydration can have on cardiac output. Less blood volume results in less cardiac output. For every 1% body weight loss comes a potential four beats/minute increase in heart rate. This is another mechanism of how stress impacts the body.

Mental focus

Proper hydration is vital for physical performance. It is also crucial for mental clarity and focus. Dehydration can lead to reduced focus and decreased accuracy in attention. Being dehydrated by just two percent has been found to impair performance in tasks requiring attention, psychomotor, and immediate memory skills, all of which are required to stay focused and safe during a workout or race. Hydrated athletes can experience enhanced confidence and a more positive mindset, contributing to overall race-day success.

Reducing fatigue

Hydration status can impact fatigue levels, as even mild dehydration can decrease energy and physical capacity. Hyperhydration may stave off early-onset fatigue during the event.

Reduced in-race drinking

Athletes might hyperhydrate to minimize the need for fluid intake during the event. This can be particularly useful when access to fluids might be limited, or if athletes are concerned large amounts of fluid in-race will cause gastrointestinal distress.

While hyperhydration offers several potential advantages, it’s essential to consider the individual variability in responses to this practice. Factors such as an athlete’s body size, sweat rate, training level, and personal preferences can influence the efficacy of hyperhydration and its potential drawbacks.

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Glycerol and sodium for hyperhydration

Glycerol and sodium are often used with hyperhydration strategies to enhance fluid retention and maintain electrolyte balance. Let’s look at how these two components assist in hyperhydration:


Glycerol is a sugar alcohol used as an osmotic agent. You can purchase Glycerol from food manufacturing suppliers as it is a thickener and sweetener food additive. Glycerol can attract and hold water, effectively increasing the total body water.

The mechanism by which glycerol assists in hyperhydration is through its osmotic effect. When ingested, glycerol moves into the body’s cells and bloodstream. As it does so, it draws water with it due to its osmotic properties. This leads to an increase in the body’s total water content, effectively creating a state of hyperhydration. Previously it was banned by WADA in 2010 for its role as a plasma volume expander. In 2018, this was overturned and is now an approved supplement with evidence to support its use in appropriate environmental conditions.


Sodium is an essential electrolyte crucial in maintaining fluid balance within the body. When sodium is present in the extracellular space, it encourages water from the intracellular space to the extracellular space, effectively expanding the body’s overall fluid volume. Sodium assists hyperhydration by influencing fluid retention. Sodium affects kidney function by promoting water reabsorption and reducing urine output via the stimulation of antidiuretic hormone (ADH). In this sense, sodium ingestion with fluids effectively retains consumed fluids, and is potentially more effective than glycerol. (For more on this, check out How Much Salt Do You Need While Training and Racing?)

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Does hyperhydration work? What the science says:

Hyperhydration triathlon running cycling how to hyperhydrate
The pros and cons of hyperhydration is an area of scientific inquiry for some sports nutrition researchers. (Photo: Getty Images)

Published in Sports Medicine, the aforementioned systematic review included 38 studies and 215 participants investigating the impact of pre-exercise hyperhydration on exercise performance, physiological outcomes, and gastrointestinal symptoms in triathletes. The participants were 90% male. Only one study included exclusively female participants. 16 of the 38 studies included did not have an exercise component. Because of these limitations, it is essential to consider all findings with an open mind and accept that this is not a black-and-white topic.

Enhanced hydration status

Pre-exercise hyperhydration significantly increases an athlete’s fluid balance, potentially reducing the risk of dehydration during the race. Two studies found high sodium doses, 164 mmol/L or 3772 mg/L, lead to a significant (44%) increase in fluid retention compared to lower sodium fluids (10 mmol/L or 230 mg/L). In those two studies, this translated to improved running performance until exhaustion at 32C / 89F at 70% VO2 max. The increased plasma volume resulted from the increased hydration status. The impact on the body is a reduced cardiac strain (improved venous return -> improved arterial pressure -> stabilizes stroke volume of heart → reduced heart rate) at constant workloads.

Time to exhaustion (TTE)

The improved cardiac function outlined likely contributed to the positive findings related to TTE. Seven studies investigated the impact of hyperhydration on TTE. Five of these studies did report a significant increase in TTE after both glycerol and sodium loading.  Cycling at 60% of maximal capacity after glycerol-induced hyperhydration resulted in improvements ranging from 14-25% in TTE during testing at 23-27ºC/73-80ºF

Time trial (TT) performance potential

Hyperhydration may improve endurance performance, although results are conflicting and equivocal. One study that simulated a triathlon found a 5.8% improved time trial (TT) performance in the glycerol-induced hyperhydration cohort. The running studies found no difference in TT performance when comparing glycerol or sodium to placebo. The cycling studies included in the review had varying results with no significant improvement in TT performance. However, most of the studies had limited duration (63-67 minutes), somewhat defeating the purpose of hyperhydration. One of the cycling studies investigating a 50-minute TT reported an 11.4% improvement in 30C/86F heat during steady-state cycling.  The benefits of hyperhydration appear to be related to a constant workload as opposed to variable efforts. This should be accounted for in practical terms when considering a race effort.


Adequate hydration assists in regulating body temperature, which is crucial during intense physical activity. Despite the potential for hyperhydration to induce cooling in the body, there is a lack of consensus for this claim — conflicting results with no impact through to 0.3-0.4C reductions in core temperature being reported for both glycerol and sodium-induced hyperhydration. The reduction in core temperature was more profound during constant work rate compared to variable work rates in the studies. Interestingly, despite one of the potential pros of hyperhydration being improved peripheral cooling, no studies found this to occur at any point during constant, variable, or mixed workloads. So, the idea of improved performance through skin cooling can be put to bed.

Gastrointestinal discomfort

26 of the 38 studies (68%) highlighted that pre-exercise hyperhydration can lead to increased gastrointestinal symptoms, including bloating, nausea, and discomfort. Reported symptoms were higher in the glycerol studies than the sodium studies, with the severity of symptoms, also reported to be worse in the glycerol groups than in the sodium and control groups. Diarrhea was reported to increase with increasing doses of sodium. This is particularly important for athletes who struggle with this issue during racing as it could be related to a high sodium intake in the consumed products. These symptoms can negatively impact an athlete’s ability to perform optimally, as gastrointestinal distress can be physically and mentally distressing.

Performance interference

The systematic review does not prove hyperhydration consistently enhances exercise performance. As noted, many studies found no significant improvement in the performance of TT or TTE when comparing hyperhydration to control. Whilst improvements in reduced heart rate were observed in several of the included studies, this did not translate to improved exercise performance. Some athletes might experience adverse effects on performance due to the discomfort caused by gastrointestinal symptoms and fluid overload.

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Considerations and recommendations for hyperhydration

Fluid imbalance

While the review focuses on hyperhydration, excessive fluid intake without proper electrolyte balance can lead to hyponatremia, a dangerous condition where blood sodium levels become dangerously low (read more about that here). This condition can have severe health consequences, and in extreme circumstances, death.

Individual variation

Athletes respond differently to hyperhydration. Some athletes benefit from the enhanced fluid reserves, while others may not.  Athletes should experiment with hyperhydration strategies during training to understand how their bodies react. Doing this under the guidance of a nutrition expert, such as a registered nutritionist or dietician, is advised.

Weight gain

Athletes must consider whether the weight gain and negative impact on running economy from hyperhydration outweigh the potential benefits. The duration of the event will often be the deciding factor in this decision.

Electrolyte balance

Hyperhydration should be paired with appropriate sodium intake to prevent imbalances that could lead to hyponatremia. Incorporating sodium-rich beverages or supplements maintains proper osmolarity levels. (See notes on how to do it below.)

Event type

Hyperhydration is rarely recommended or required when an event supplies adequate hydration opportunities. Most athletes do not need hyperhydration as their sweat rate does not warrant the intervention. Athletes should gain an understanding of their sweat rate through repeated measures of body weight losses during bike and run sessions across multiple intensities and environmental conditions. Using an app like Fuelin to track weight loss through sweat is one solution to gain a thorough insight into your hydration needs.

Race simulation

Practicing hyperhydration during training sessions that simulate race conditions can help athletes gauge its impact on their performance and comfort levels. For triathletes, this should involve the bike and run components of racing, ideally in combination with repeated brick sessions.

Testing and recording

Completing measurements of body weight before and after the sessions to calculate sweat rate loss and fluid requirements is essential to learning to hyperhydrate. Fuelin provides all the tools to enable this within their app.

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When and how to hyperhydrate

A hyperhydration strategy is best developed in tandem with a sports nutrition expert, as this person can help you dial in the formulation that is best for your unique needs. Hydration is not a one-size-fits-all approach – we know, for example, that men and women have unique hydration needs, even when competing in the same event. It’s also critical to practice this hyperhydraton plan by consuming the fluid the night before big workouts (like a long bike ride or brick) to see how your body tolerates and performs.

Sodium loading

The concentration of the fluid is the key element – you are attempting to mimic blood sodium concentration. This is, therefore, a very salty solution and may only be tolerable for a few athletes.

  • 10-25 ml/kg (4-10 ml/lb) fluid
  • 2-4 hours before exercise/event
  • 130-164 mmol/L  = 2990 – 3772 mg/L


  • 70 kg / 154 lbs athlete
  • 700ml fluid with 2093mg sodium (130 mmol/L) up to 1750 ml with 6601 mg sodium (164 mmol/L)
  • 2-4 hours before exercise/event

Glycerol loading

An analysis of the studies in this area indicates that endurance athletes intending to hyperhydrate with glycerol could use the following protocol.

  • Ingest glycerol 1.2 g/kg BW in 26 mL/kg/body weight of fluid 
  • Consume over 60 minutes, 
  • Consume 2 to 4 hours before exercise.” 


  • 70 kg athlete 
  • 84g glycerol in 1.8L of water 
  • Consumed over 60 minutes 
  • 2 to 4 hours before the event.
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Final thoughts on hyperhydration

Hyperhydration is a strategy that could be used to enhance athletic performance. Athletes aim to optimize their hydration status, thermoregulation, and endurance by intentionally increasing fluid reserves before an event. However, this approach has challenges, including the potential for gastrointestinal discomfort and electrolyte imbalances. Athletes considering hyperhydration should approach it cautiously. It is important to practice hyperhydration under guidance during training sessions.  This will provide insight into the impact on your body. Consulting with sports nutrition experts and tailoring hyperhydration strategies to individual needs can help athletes make informed decisions about integrating this practice into their race-day routines. Ultimately, the goal is to balance hydration optimization and minimize potential adverse effects on performance and well-being. For the majority of athletes, hyperhydration is not recommended or required.

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