In brief: To study the effects of diuretics on performance and neuromuscular function, the authors examined 46 male athletes before and after a 48-hour weight loss regimen. One group took a diuretic (furosemide, 1.7 mg-kg1), one group exercised, and one group served as a control. During maximal cycle ergometry the diuretic group had marked decreases in VO2, O2pulse, work load, ventilation, and tidal volume compared with the control group.Electromyographical examination showed striking differences in nerve reactivity after diuretic use. Therefore, taking diuretics to achieve a rapid weight loss may be hazardous. Athletes can lose a similar amount of weight through exercise, which has fewer side effects.