Sauna-induced dehydration is an effective way for athletes competing in weight class events to lose weight rapidly before competition, according to a new study from Spain. However, female athletes may find the weight loss benefits cancelled out by a decrease in explosive power.

Athletes competing in such events as weight-lifting, judo, karate, boxing, rowing and canoeing are sometimes faced with the need to lose weight in order to compete in their desired category. In theory, this should be accomplished gradually over a few months, but in practice body weight is sometimes just above the specified limit of a weight category, and drastic last-ditch measures are called for.

Methods commonly used (but not recommended) for dehydration-induced rapid weight loss include vomiting, laxatives, diuretics and sauna, all of which may have negative effects on mood, health and performance, mostly due to inadequate fluid replacement in the period between weigh-in and competition.

The Spanish study was set up to investigate whether sauna-induced dehydration is an effective way to shed body weight rapidly and whether the practice has any detrimental effect on strength and explosive power.

Six male and six female athletes, who were not familiar with ‘making the weight’ procedures, were tested on three occasions:

1. Before sauna;
2. After three consecutive 20-minutes sauna sessions at 70°C, separated by five-minute rest intervals;
3. After a one-hour rehydration period, during which the athletes ingested a carbohydrate drink at 2.5ml per kg of body weight every 15 minutes.

Testing focused on body composition, strength (row strength and handgrip strength) and jump capacity (squat jump, counter-movement jump and elastic capacity).

Sauna-induced dehydration was effective in inducing significant weight loss in men and women (1.8% and 1.4% respectively), but rehydration reversed the reduction only partially.

And, although male performance was unaffected by the weight loss, squat jump performance in women was shown to be impaired after rehydration by an amount which was linearly and directly related to the percentage loss of body weight.

The researchers speculate that this observed difference between men and women may be attributable to the influence of sex hormones on water metabolism and handling. In the light of this they advise that alternative rehydration schemes should be researched and devised for women.

Int J Sports Med 2003; 24:518-522