Rehydration

Marcin Lewandowski

Water plays many important roles within the body, and hydration refers simply to the amount of fluid present. If you have too little fluid in your body – or too much – this can prevent your body working optimally. It’s the single largest constituent of your body (60% if you’re male, or 50-55% if you’re female). Crucially, it’s also 70% of your muscle mass. Fluid ingestion is critical to the safe, effective functioning of the body. It plays a critical role in our bodily functions and regulates body temperature.

Fluid leaves the body in several ways, most notably through urination and sweating. Sweat rates can range between 0.5 to 2.0 litres per hour depending on the sport you’re playing and the environment in which you’re playing.1-5 There is no ‘one size fits all’ recommendation for fluid intake since sweat rates vary from person to person.

Good hydration is essential for health and wellness and the body water content is usually maintained within 1-2% of the ideal level on a daily basis.

To maintain a high level of sporting performance, it’s critical you stay properly hydrated. Loss of fluid by as little as 2% of body mass (that’s 1.4 kg for a 70kg individual) can reduce both physical and mental performance.6-14

Physical performance impairments occurring from lack of proper hydration include

  • Reduced stamina
  • Reduced sprint performance
  • Reduced pace 

Mental performance impairments occurring from lack of proper hydration include

  • Reduced concentration, attention and reaction time
  • Reduced visual / motor skills and accuracy (hitting the target or scoring a goal becomes harder to achieve)
  • Reduced judgement

After you’ve exercised, you should start rehydrating as soon as possible. If you’re doing continuous bouts of exercise – from circuits at the gym to competing in a triathlon – don’t forget to rehydrate properly between each one, otherwise you’ll start your next exercise session in a dehydrated state, which is likely to damage your overall performance.

  • Ideally you’ll drink 150% of the fluid you’ve lost during a session in the hours after.11
  • Aim to drink 1.5 litres of fluid for each kilogram of your bodyweight lost as sweat.11 To calculate this, simply weigh yourself before and after a training session.

REMEMBER - Always weigh yourself barefoot and wearing minimal clothing.

References
  • 1Murray B. 2007. Hydration and Physical Performance. Journal of the American College of Nutrition, Vol. 26, No. 5, 542S–548S.
  • 2Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS. American College of Sports Medicine Position Stand: Exercise and Fluid Replacement. Med Sci Sports Exerc. 2007; 39(2): 377-390.
  • 3Coyle EF: Fluid and fuel intake during exercise. J Sports Sci 22:39–55, 2004.
  • 4Maughan, R.J. and R. Murray, 2001. Sports Drinks: Basic Science and Practical Aspects. CRC Press LLC, Boca Ranton, FL, USA.
  • 5Rehrer NJ, Burke LM: Sweat losses during various sports. Aust J Nutr Diet 53:S13–S16, 1996.
  • 6Murray B. 2007. Hydration and physical performance. J. Am. Coll. Nutr., 26: 542S-548S.
  • 7Grandjean A. & Grandjean N. 2007. Dehydration and Cognitive Performance . Journal of the American College of Nutrition, Vol. 26, No. 5, 549S–554.
  • 8Fallowfield, J.L., Williams, C., Booth, J., Choo, B.H. and Growns, S. (1996). Effect of water ingestion on endurance capacity during prolonged running. Journal of Sports Sciences, 14, 497–502.
  • 9McConell, G., Stephens, T. and Canny, B. (1999). Fluid ingestion does not influence intense 1-h exercise performance in a mild environment. Medicine and Science in Sports and Exercise, 31, 386–392.
  • 10Cheuvront SN, Carter R, Castellani JW, Sawka MN. 2005. Hypohydration impairs endurance exercise performance in temperate but not cold air. J. Appl. Physiol., 99: 1972-1976.
  • 11Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS. 2007. Exercise and fluid replacement. Med. Sci. Sports Exerc. 39: 377-390.
  • 12Sims ST, Rehrer NJ, Bell ML, Cotter JD. 2007. Preexercise sodium loading aids fluid balance and endurance for women exercising in the heat. J. Appl. Physiol., 103: 534-541.
  • 13Lieberman H. 2007. Hydration and Cognition: A Critical Review and Recommendations for Future Research. Journal of the American College of Nutrition, Vol. 26, No. 5, 555S–561S.
  • 14Cian C, Koulmann N, Barraud P, Raphel C, Jimenez C, Melin B: Influence of variations in body hydration on cognitive function: effect of hyperhydration, heat stress, and exercise-induced dehydration. J Psychophysiology 14:29–36, 2000.

This information is not medical advice and should not replace consultation with your health care provider or nutritionist before starting a new exercise program or eating plan.