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The Effects of Dehydration on Physical & Cognitive Performance

Introduction

Dehydration is defined as the state of losing more fluid than what you take in. It has been found to significantly affect both physical and cognitive performances. This article will present some of the most prevalent bodies of research on the effects of dehydration on performance and cognitive function. 

We will begin by focusing on the impact of dehydration on aerobic and anaerobic performance, following which we’ll present multiple studies which look into its effects on strength, power and prolonged effort training. 

We will then discuss the issues surrounding dehydration and its effects on recovery, muscle soreness and perceived rates of exertion, following which the data around dehydration and its effects on cognitive function will be presented.

The Effects of Dehydration on Athletic Performance

Dehydration’s Effects on Aerobic Performance

Dehydration has been found to affect various types of physical performance. Aerobic performance, which is defined by cardiovascular efficiency and endurance, is notably affected. Research by Cheuvront et al. (2003) indicates that 2% dehydration (indicated by a 2% loss in body mass) can reduce aerobic performance by up to 10%, negatively impacting endurance activities such as long distance running and cycling. 

Dehydration’s Effects on Anaerobic Performance

Anaerobic performance, which involves short bursts of high intensity activity such as weightlifting or sprinting, has been found to also suffer as a result of dehydration, with studies showing decreased strength and power output. A study by Judelson et al. (2007) found that dehydration resulted in a 4.8% reduction in peak power output during anaerobic exercise. 

Intermittent sprint performance, which is instrumental for performance in sports such as football and basketball, has also been found to be impaired due to reduced energy and increased perceived exertion. According to a study by McGregor et al. (1999), a degree of 2% dehydration led to a significant decrease in sprint performance and increased fatigue in soccer players. 

Further research has looked at how high intensity performance, demanding quick recovery and sustained effort, declines as dehydration affects muscle function and thermoregulation. For instance, a study by Sawka et al. (2007) showed that dehydration significantly impairs high intensity exercise performance, with most notable effects on muscular endurance and strength.

Dehydration’s Effects on Strength, Power & Prolonged Effort Training

Dehydration is known to have a substantial negative impact on strength, power and resistance training performance, particularly in prolonged, intense workouts such as CrossFit and Hyrox. Strength and power output have been shown to be particularly affected, with research by Judelson et al. (2007) showing a significant 3% decrease in strength during resistance training when dehydrated. 

Being in a state of dehydration has been proven to impair muscle function in strength training workouts, whilst also reducing the ability to sustain high intensity efforts. A study by Schoffstall et al. (2001) found that dehydration led to a significant decline in muscular endurance and power during resistance exercises. The research looked specifically at ten weight trained males carrying out a bench press one rep max (1RM). They found that passive dehydration of just 1.5% loss of body mass adversely affected 1RM performance. This adverse effect was then overcome following rehydration and a 2 hour rest period.

Further research on CrossFit Athletes, who combine high intensity strength and conditioning workouts, has shown a negative impact on performance from dehydration. A study by Hayes and Morse (2010) demonstrated that just 2% dehydration resulted in decreased performance in CrossFit workouts, affecting both strength and endurance components. 

Dehydration & Endurance Activities

Numerous studies have consistently demonstrated the negative effects of hypohydration (dehydration) on endurance activities. For instance, Goulet (2012) conducted a meta analysis showing that dehydration significantly reduces endurance performance by approximately 2-7%, depending on the severity and duration of dehydration. However, methodological variables such as the method of inducing dehydration, the type of exercise performed, and environmental conditions may also influence these findings. 

Sawka et al. (2007) highlight that dehydration impacts cardiovascular function, thermoregulation, and muscle metabolism, which are critical for endurance performance. Furthermore, Kenefick (2018) pointed out that studies using exercise induced dehydration versus passive dehydration methods might yield different results due to varying stress levels on the body. 

The research tells us that rehydration reverses these negative effects of dehydration. Montain et al. (1999) found that rehydrating with 150% of the total body mass lost through sweat improved endurance performance by 6-8%. 

Dehydration’s Effects on Recovery

Recovery is crucial for maintaining performance in sustained, and dehydration hinders this process by reducing the rate of muscle glycogen resynthesis and increasing muscle soreness. 

A study by Cheuvront et al. (2003) and again in 2014 showed that adequate hydration is essential for effective recovery, as dehydration prolongs the recovery time needed between training sessions.

Dehydration also impairs protein synthesis, which is required for muscle repair and growth. Further studies on recovery demonstrate that muscle protein synthesis rates are reduced when participants were dehydrated by just 2% body mass (Tipton et al., 2001). Research from Waldegger et al. (1997) confirmed that a reduction in cell volume correlates with a catabolic environment, which favours muscle protein breakdown, rather than anabolic environment.

The findings reviewed support that proper hydration is therefore critical for maintaining performance and recovery in strength, power and resistance training.

Dehydration & Muscle Soreness

Fluid balance and dehydration has  been found to significantly impact muscle damage, soreness, and protein synthesis. Research indicates that dehydration exacerbates muscle damage and delays recovery. A study by Casa et al. (2010) found that dehydrated athletes experienced increased muscle soreness and higher levels of creatine kinase, a marker of muscle damage, compared to well hydrated counterparts.

Additionally, Judelson et al. (2008) report that dehydration leads to a significant decrease in muscle strength and increased muscle soreness post exercise, hindering overall recovery. We can conclude then that proper hydration is therefore a key factor for minimising muscle damage, reducing soreness, and promoting efficient protein synthesis and muscle recovery post exercise. These findings really highlight the importance of maintaining fluid balance for maintaining proper muscle function and optimised athletic performance.

How Dehydration Affects Rate of Perceived Exertion

Fluid balance and dehydration significantly impact perceived exertion during physical activity. Research consistently shows that dehydration increases the perception of effort. For example, a study by Casa et al. (2010) found that athletes who were dehydrated reported higher ratings of perceived exertion (RPE) compared to those who were well hydrated, even when performing the same exercise intensity. 

Additionally, Sawka et al. (2007) demonstrated that dehydration of as little as 2% body mass increased RPE by 8 10%, highlighting the body's heightened sense of effort when fluid levels are low. Another study by Cheuvront et al. (2003) showed that during endurance exercise, dehydrated participants not only felt more fatigued but also perceived the exercise as more strenuous compared to their hydrated state. These findings highlight the importance of maintaining proper hydration to reduce perceived exertion, and improve exercise performance.

How Dehydration Impacts Muscle Cramping

Dehydration is often linked to muscle cramps, although the relationship is complex and not completely understood. Research suggests that dehydration can contribute to muscle cramping, particularly in hot and humid conditions. 

A study by Schwellnus et al. (2004) found that athletes who experienced muscle cramps had significantly lower levels of hydration compared to those who did not cramp. Another study by Miller et al. (2010) showed that electrolyte imbalances, often accompanying dehydration, can exacerbate muscle cramping by disrupting normal muscle function. 

More research, such as that by Bergeron (2008), indicates that whilst dehydration may increase susceptibility to muscle cramps, factors such as muscle fatigue and neuromuscular control also play significant roles. This suggests that maintaining proper hydration can help reduce the risk of cramps but may not be the sole factor. Ensuring adequate fluid and electrolyte intake is vital for preventing muscle cramps and optimising muscle function.

How Dehydration Affects Cognitive Performance

There are various studies which demonstrate that rehydrating following a period of dehydration significantly improves both physical and mental performance. A study by Shirreffs et al. (2004) highlights that participants showed improved attention and memory tasks after rehydrating following a period of dehydration. The review emphasises that the timing, volume, and type of fluid consumed are key for optimal recovery. 

Further research from Smith et al. (2012) found that dehydration levels of 2% body mass loss led to a notable decline in attention and short term memory. Another study by Gopinathan et al. (1988) reported that reaction time and psychomotor skills were adversely affected when participants were dehydrated by 2.8% of their body mass. It’s highlighted that the severity of cognitive impairment correlates with the degree of dehydration, with higher deficits observed in tasks requiring sustained attention and executive function. 

Furthermore, Cian et al. (2000) demonstrated that even mild dehydration (1-2% of total body mass loss) can reduce cognitive performance in complex tasks involving memory and attention, really showing the importance of maintaining hydration to preserve cognitive function, particularly during activities that induce sweating and fluid loss.

Fluid balance and dehydration has also been shown to significantly impact mood, concentration, and performance in the workplace. Research indicates that even mild dehydration can adversely affect cognitive functions and emotional states. For instance, a study by Ganio et al. (2011) found that dehydration of 1-2% body mass negatively influenced mood, causing increased fatigue, tension, and anxiety, while also impairing concentration and working memory. Another study demonstrates that individuals who are dehydrated have slower reaction times and decreased alertness (Benton and Young, 2015))

Further research reports that dehydration resulted in a significant decline in subjective feelings of alertness and an increase in the perceived effort to complete cognitive tasks (Pross et al., 2013). These findings show the importance of maintaining adequate hydration to support optimal mood, concentration, and overall performance, emphasising that proper fluid intake is required for sustaining productivity.

Conclusion

The research reviewed in this article presents the data showing the negative impact of dehydration on both physical and cognitive performance. Physiologically, dehydration has an acute negative impact on both aerobic and anaerobic performance, impairing strength, power, and endurance in high intensity workouts, whilst also hindering recovery and muscle function. 

Deficits in cognitive performance are also prevalent with dehydration, including decreased concentration, memory, and increased perception of effort, which notably affect performance and mood. 

Overall, the studies presented emphasise the significant role that staying hydrated plays for maintaining optimal physical performance, effective recovery, and cognitive functions, highlighting the need for consistent, adequate fluid intake to mitigate the adverse effects of dehydration.

Maintaining electrolyte balance, particularly with sodium, has been found to improve hydration  and thus performance through promoting better water retention and stimulating thirst, which helps maintain hydration better than just drinking water on its own (Del Coso et al., 2016). Further research shows that supplementation with salt and potassium may be beneficial for restoring electrolyte balance, thus aiding hydration following prolonged exercise efforts (Maughan & Shirreffs, 1997). If you’re looking to increase your electrolyte intake to help optimise your hydration, then be sure to take a look at our electrolyte drink.


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