The Effects of Dehydration on Physiological Functioning

by Dave Coles MSc BA (Hons) PGCE
WJA 5th Dan, Senior Club Coach and 1999 u90kg World MasterAthlete Champion

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Previous research identified that many judoka use rapid weight-loss methods in order to make their fighting weight (Coles 1999). The most commonly reported methods of reduced fluid intake, the use of sauna/steam rooms, and exercising in sweat kit inevitably lead to dehydration, which can have a negative effect on performance.

During prolonged exercise in hot environments, water losses of up to 3 litres per hour have been reported, with 90 percent of this total loss occurring through sweating (Wilmore and Costill, 1994). For the judoka struggling to make their weight, each litre of sweat lost in the sauna, steam room or through exercising in sweat kit will be “rewarded” with approximately 1 kg of lost body weight. This may seem an attractive prospect as the judoka tries to make their weight, however in order to facilitate optimal physiological functioning, the body’s water and electrolyte content should remain relatively constant. Many investigations have been carried out into the effects of dehydration on physiological functioning. Dehydration has been shown to reduce blood plasma volume, this results in a decrease in the amount of blood pumped out by the heart, consequently the heart has to work harder in an attempt to maintain an adequate blood (oxygen) supply to the working muscles (Robergs and Roberts, 1997; Clarkson, 1998). Dehydration has been shown to decrease testosterone levels (Booth et al., 1993; Viscardi, 1998), increase blood lactate accumulation (Wilmore and Costill 1994), and impair the body’s ability to sweat, resulting is an increased risk of overheating (Armstrong, 1992; ACSM, 1996).

Armstrong (1992, p.29) suggests, “Dehydration results in reduced muscle blood flow, waste removal, and heat dissipation, all of which are necessary for sustained, high power muscle action in events such as boxing and judo.”

Taken to the extreme, rapid weight loss when achieved through dehydration can be fatal. Viscardi (1998) identifies that excessive dehydration can harm bodily functions, leading to kidney failure, heat stroke or heart attack, indeed in 1997, within a period of thirty-three days, three young American collegiate wrestlers tragically died whilst trying to ‘make their weight’ (Hickling, 1999).

Does re-hydration work?

After completing the weigh-in, judoka typically try to rapidly replace lost body fluids in an attempt to return to a normal state of hydration. However, the judoka is unlikely to eat and drink sufficiently because of the negative effects of fighting on a full stomach. In many cases the time between the weigh-in and first contest is usually insufficient for fluid and electrolyte balance to be fully re-established in muscles, or for the rehydration and replenishment of muscle and liver glycogen (ACSM, 1996; Yankanich et al., 1998; Clarkson, 1998). Horswill et al. (1990, p.470) state, “The period between the weigh-in and competition is probably not enough time for wrestlers, boxers, and judo athletes to replace muscle glycogen.” This is supported by Foster (1995, p.66) who identified that “The body takes from 4 to 48 hours to fully recover from moderate dehydration, which means there isn’t enough time between weigh-in and the match to ensure peak performance and health.”


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Dave Coles currently lectures in Physical Education, Sport and Recreation at Herefordshire College of Technology and can be contacted via [email protected]. All rights reserved. This HTML version was created and copyright © 2002 by Neil Ohlenkamp,, USA. Last modified September 23, 2002.