Does Dehydration Affect Sport Performance?

Dehydration does not seem to affect simulated soccer performance.

For as critical as dehydration is supposed to be for performance, only a few studies have tried to determine its effects on the performance of actual sports.  A likely reason for this is that it’s quite hard to measure sport performance during a practice or game.  There are so many factors in play and not one metric can tell you if individual “performance” is increased or decreased.  When considering how hard it is to measure sport performance in the field, the next logical step would be to attempt to mimic the sport of interest in a clinical setting where the investigator has more control over the type/style/duration of exercise and can monitor work performed by a subject (literally: “performance”).

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Does Dehydration Affect Sprint Exercise Performance?

Dehydration is a fairly common buzzword known by recreational and elite athletes alike.  We know that it’s bad, and that we should prevent it, but why?  Does dehydration actually affect our body’s ability to do work?  Without worrying about all of the factors affecting sport performance for now, this post will look at whether dehydration imposes a physical limitation for us during exercise.

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Does Dehydration Affect Exercise Performance?

Dehydration Reduced 5000m and 10000m Runing Performance

Dehydration is a fairly common occurrence in competitive sports, and exercise in general.  Even moderate dehydration (losing 2% of your pre-exercise body mass) has been shown to impair exercise performance.  When moderate dehydration (~2% of pre-exercise body mass) was induced by giving athletes diuretics, 1500, 5000 and 10000m running speed decreased (-10, -19 and -18 metre/min), resulting in a slower race time (+0.2, +1.3 and +1.6 min) compared to when the same subjects raced without diuretics (1).

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Is Dehydration a Risk for Athletes?

Dehydration is consistently observed in athletes playing both team sports and individual match play.  Many studies have described fluid losses in sports such as running (1, 18, 25), cycling (6, 7), basketball (2, 5, 8), soccer (13-16, 21), American football (9-12, 22-24), tennis (3, 4, 17) and ice hockey (19, 20).

Athletes are at Risk of DehydrationThe results from these studies are surprisingly consistent.  First, the average athlete tends to start exercise already mildly dehydrated (USGa≈ 1.020).  They then dehydrate further (1-2% body massb), regardless of whether they are participating in a practice or game.  They will typically sweat 1-2 L/hr and replace only 67% of the sweat they lose while exercising.  Many athletes choose to replace these sweat losses with water, however sweat contains a large amount of sodium (1100-1600 mg/L), which is not replaced by ingesting water.  Note that the Recommended Daily Allowance for sodium in Canada and the USA is 1500 mg – an amount that can easily be lost in 1 hour of exercising.  The combination of moderate sweat rates and moderate high sweat sodium concentrations can result in large total sodium losses (1100-4800 mg) for many athletes.

Perhaps the most important idea to pull from these studies is that they underscore the how variable sweat loss, fluid intake, sodium loss and dehydration are between athletes.  Some players are genetically predisposed to heavy sweat rates and low sodium losses, while others are the exact opposite.  Importantly, some athletes exhibit moderate to large sweat losses, and moderate to large sodium concentrations, which make them at particular risk for the negative effect of dehydration.  These athletes should be particularly concerned with staying well-hydrated in order to avoid decreases in athletic performance.

a USG = Urine Specific Gravity.  This is a measure of the density of urine, a higher number means higher concentration, and more dehydrated and vice-versa.
b Dehydration is measured relative to body mass, and 1-2% body mass loss has been associated with reduced exercise performance.


1.  Armstrong LE, Costill DL and Fink WJ. Influence of diuretic-induced dehydration on competitive running performance. Med Sci Sports Exerc. 17(4): 456-461, 1985.
2.  Baker LB, Dougherty KA, Chow M and Kenney WL. Progressive dehydration causes a progressive decline in basketball skill performance. Med Sci Sports Exerc. 39(7): 1114-1123, 2007.
3.  Bergeron MF. Voluntary fluid intake and core temperature responses in adolescent tennis players: sports beverage versus water. Br J Sports Med. 40(5): 406-410, 2006.
4.  Bergeron MF, Maresh CM, Armstrong LE, Signorile JF, Castellani JW, Kenefick RW, Lagasse KE and Riebe DA. Fluid-electrolyte balance associated with tennis match play in a hot environment. Int J Sport Nutr. 5(3): 180-193, 1995.
5.  Carvalho P, Oliveira B, Barros R, Padrão P, Moreira P and Teixeira VH. Impact of fluid restriction and ad libitum water intake or an 8% carbohydrate-electrolyte beverage on skill performance of elite adolescent basketball players. Int J Sport Nutr Exerc Metab. 21(3): 214-221, 2011.
6.  Davis JM, Jackson DA, Broadwell MS, Queary JL and Lambert CL. Carbohydrate drinks delay fatigue during intermittent, high-intensity cycling in active men and women. Int J Sport Nutr. 7(4): 261-273, 1997.
7.  Davis JM, Welsh RS and Alerson NA. Effects of carbohydrate and chromium ingestion during intermittent high-intensity exercise to fatigue. Int J Sport Nutr Exerc Metab. 10(4): 476-485, 2000.
8.  Dougherty KA, Baker LB, Chow M and Kenney WL. Two percent dehydration impairs and six percent carbohydrate drink improves boys basketball skills. Med Sci Sports Exerc. 38(9): 1650-1658, 2006.
9.  Godek SF, Bartolozzi AR, Burkholder R, Sugarman E and Peduzzi C. Sweat rates and fluid turnover in professional football players: a comparison of National Football League linemen and backs. J Athl Train. 43(2): 184-189, 2008.
10.  Godek SF, Bartolozzi AR and Godek JJ. Sweat rate and fluid turnover in American football players compared with runners in a hot and humid environment. Br J Sports Med. 39(4): 205-211; discussion 205-211, 2005.
11.  Godek SF, Godek JJ and Bartolozzi AR. Hydration status in college football players during consecutive days of twice-a-day preseason practices. Am J Sports Med. 33(6): 843-851, 2005.
12.  Horswill CA, Stofan JR, Lacambra M, Toriscelli TA, Eichner ER and Murray R. Sodium balance during U. S. football training in the heat: cramp-prone vs. reference players. Int J Sports Med. 30(11): 789-794, 2009.
13.  Kurdak SS, Shirreffs SM, Maughan RJ, Ozgünen KT, Zeren C, Korkmaz S, Yazici Z, Ersöz G, Binnet MS and Dvorak J. Hydration and sweating responses to hot-weather football competition. Scand J Med Sci Sports. 20(Suppl 3): 133-139, 2010.
14.  Maughan R, Shirreffs S, Merson S and Horswill C. Fluid and electrolyte balance in elite male football (soccer) players training in a cool environment. J Sports Sci. 23(1): 73-79, 2005.
15.  Maughan RJ, Merson SJ, Broad NP and Shirreffs SM. Fluid and electrolyte intake and loss in elite soccer players during training. Int J Sport Nutr Exerc Metab. 14(3): 333-346, 2004.
16.  Maughan RJ, Watson P, Evans GH, Broad N and Shirreffs SM. Water balance and salt losses in competitive football. Int J Sport Nutr Exerc Metab. 17(6): 583-594, 2007.
17.  Morante SM and Brotherhood JR. Thermoregulatory responses during competitive singles tennis. Br J Sports Med. 42(9): 736-741, 2008.
18.  Nicholas CW, Tsintzas K, Boobis L and Williams C. Carbohydrate-electrolyte ingestion during intermittent high-intensity running. Med Sci Sports Exerc. 31(9): 1280-1286, 1999.
19.  Palmer MS, Logan HM and Spriet LL. On-ice sweat rate, voluntary fluid intake, and sodium balance during practice in male junior ice hockey players drinking water or a carbohydrate-electrolyte solution. Appl Physiol Nutr Metab. 35(3): 328-335, 2010.
20.  Palmer MS and Spriet LL. Sweat rate, salt loss, and fluid intake during an intense on-ice practice in elite Canadian male junior hockey players. Appl Physiol Nutr Metab. 33(2): 263-271, 2008.
21.  Shirreffs SM, Aragon-Vargas LF, Chamorro M, Maughan RJ, Serratosa L and Zachwieja JJ. The Sweating Response of Elite Professional Soccer Players to Training in the Heat. Int J Sports Med. 26(2): 90-95, 2005.
22.  Stofan JR, Osterberg KL, Horswill CA, Lacambra M, Eichner ER, Anderson SA and Murray R. Daily fluid turnover during preseason training in U.S. college football. Int J Sport Nutr Exerc Metab. 17(4): 340-351, 2007.
23.  Stofan JR, Zachwieja JJ, Horswill CA, Murray R, Anderson SA and Eichner ER. Sweat and sodium losses in NCAA football players: a precursor to heat cramps? Int J Sport Nutr Exerc Metab. 15(6): 641-652, 2005.
24.  Stover EA, Zachwieja J, Stofan J, Murray R and Horswill CA. Consistently high urine specific gravity in adolescent American football players and the impact of an acute drinking strategy. Int J Sports Med. 27(4): 330-335, 2006.
25.  Welsh RS, Davis JM, Burke JR and Williams HG. Carbohydrates and physical/mental performance during intermittent exercise to fatigue. Med Sci Sports Exerc. 34(4): 723-731, 2002.

What Causes Dehydration during Exercise?

There are 2 things that cause dehydration - sweating and not drinking enough.  Sweating is an automatic response to exercise and there is very little that you can do about it, but you have a lot of control over how much you drink!

 

Sweating
Salt build-up is an effect of excessive sweating that can lead to dehydration

We sweat when we get hot, because our bodies like to operate between 36-39°C (96.8-102.2°F for my American friends).  We all know from personal experience that we get hot when we exercise, but why?  What is quite amazing is that only 20% of the energy we use while exercising is devoted to actual motion – to the exercise itself.  The remaining 80% gets lost as heat!  We are terribly inefficient organisms when it comes to exercise.

Heating the body with exercise does have some benefits: it helps loosen tight muscles, makes body fluids less viscous, and increases the activity of all the enzymes that we need in order to produce energy in the muscles.  Still, wasting 80% of our energy as heat seems like overkill and we could probably get by with only 20-40% spent on heat production.  Unfortunately there is very little we can do about it.

We’ve responded to this inefficiency over time, by evolving a system that lets fluid out onto the skin to help cool it.  When sweat evaporates from the skin, the process of evaporation “steals” energy (heat) from the skin.  We can lose heat in other ways: radiation and/or convection to the environment, conduction through the skin to a colder surface, but we lose much more heat with evaporative heat loss.  It is the most efficient method that we, as humans, have to dissipate heat.

 

Drinking

The downside of this strategy that we‘ve chosen to combat increases in body temperature is that we lose body water.  There is nothing we can do to regain the fluid that we lose as sweat.  Sweat can’t be reabsorbed, spraying yourself with a hose won’t help you replace that water either – even swimmers can get dehydrated!

Fluid ingestion can restore the fluid you lose as sweat - preventing the negative effects of dehydrationThe only way that we can account for this fluid loss is by ingesting some other fluid while

exercising.  In an ideal world you would be able to gauge how much sweat you lose, and replace an equal volume of fluid (along with the ions and minerals that go with it).  In theory, from your body’s point of view everything would stay the same in these circumstances.  This is much harder than it sounds though – in my experience recreational athletes, all the way up to elite athletes, will only replace 60-70% of the fluid they lose as sweat if they’re left to ingest fluids voluntarily.

Drinking enough fluid to compensate for the sweat we lose during exercise can be difficult, and in some cases you will need to practice ingesting fluid!  If you ignore fluid replacement, though, you will certainly have to deal with the negative effects of dehydration.

The precise amounts, practices and recommendations are covered in detail in other posts.  This post is simply intended to describe in general terms the purpose of drinking.

What is “Dehydration”?

Where is water in the body?

Dehydration is literally the removal of water from an organism.  When talking about sport performance, we are that organism, and so when you are dehydrated, your body simply contains less water than it normally does.  The definition really is that simple, but what comes next is a bit more complicated.  In order to understand how dehydration negatively affects performance, we need an idea of how and where water is stored in our body, and what it does for us.

 

How much water do our bodies normally contain?

On average, your body is 60% water.  This means that:

  • a 60kg person is made up of 36L of water (we assume 1kg = 1L).
  • a 70kg person is made up of 42L of water.
  • an 80 kg person is made up of 48L of water, etc.
This is a lot of water, and your first thought might be that the amount of sweat you lose while exercising for an hour would be trivial, in comparison.  Well, at first glance it is, but the negative effects of dehydration have a lot to do with where that water is stored in the body.

 

Where is that water?

If we stick with the example of a 70kg person (42L of body water), the first thing we notice when we look inside the body is that the water is split into 2 main compartments – inside the cells and outside the cells (also called intracellular and extracellular).

Inside – Roughly 2/3 of our total body water is located inside the cells in our body.  Brain cells, muscle cells, bone cells, liver cells etc. all contain water.  In total, 28L of our 42L is contained within our cells.

Outside – The remaining 1/3 of our body water (14L of our body’s 42L) is kept outside of the cells.  At first it’s hard to imagine there being much need for water outside of a cell, but this space can be broken down even further:

  • 11L of the fluid that is kept outside of our cells is located between the cells (called interstitial fluid). This fluid helps transmit signals and transport substances from one cell to another.
  • 3L of this fluid is kept in our arteries and veins as blood, and this is what carries nutrients and oxygen (via red blood cells) to the tissues.  This 3L is vitally important.  When compromised, it is one of the main reasons that dehydration negatively affects the body.

What does water do in our bodies anyways?

Water inside the cells:

  • Ensures enzymes and chemical processes function properly.
  • Helps maintain proper neural signal transmission.
  • Facilitates energy storage and replacement after exercise (i.e. liver and muscle glycogen)

Water outside the cells:

  • Maintains blood volume.
  • Provides constant supply of oxygen and nutrients to tissues.
  • Removes carbon dioxide and waste products from tissues.
  • Regulates body temperature through thermal sweating.
  • Cushioning and lubricating properties.

 

Water plays a pretty pivotal role in keeping our bodies working properly, and really – in life as we know it.  As I hinted above, the water contained within our blood is the most important fluid space when it comes to sport and exercise performance.

I’ll have much more on the specifics of how dehydration affects this fluid space, as well as some simple techniques that you can use the same day to combat dehydration.  In the meantime, I’d love to know what you think, or if you have any questions about water’s role in the body.  Just leave a comment below and I’ll do my best to help you out!

Welcome to EffectsofDehydration.com!

Severe effects of dehydration

If you’re reading this then you’ve probably got concerns about dehydration and how it affects your sport performance.

The effects of dehydration can range from:

  • mild tiredness
  • a lack of coordination
  • general mental and physical fatigue

To more severe consequences such as:

  • impaired thermoregulation
  • heat stress
  • impaired muscular and cognitive function
  • muscle cramps

It is very rare to experience consequences that are more severe than these during competition, but in extreme cases dehydration can be fatal.

 

My number 1 goal with this blog is to teach you how to hydrate properly.  I also want to help you understand how and why dehydration is a concern during competition.  In many cases the risk of dehydration is very small, and you don’t need to to be concerned.  In other cases dehydration can negatively affect your performance, but with the proper knowledge these negative side-effects can be avoided.

Please take a minute to leave a comment below and let me know what YOU want to know.  What dehydration-related problems are you currently facing?  What solutions have you tried in the past that have, or haven’t worked?  I’m really excited to help you in any way I can!

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