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).
The 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.