ORIGINAL ARTICLE Vahur O È oÈ pik á Mati PaÈ aÈsuke á Saima Timpmann Luule Medijainen á Jaan Ereline á Tamara Smirnova Effect of creatine supplementation during rapid body mass reduction on metabolism and isokinetic muscle performance capacity Accepted: 18 December 1997 Abstract Well-trained subjects n 6 were studied before and after losing a mean 3.0%±4.3% of body mass to determine whether muscle performance could be maintained or even enhanced by dietary creatine sup- plementation. During a 5-day period of loss of mass the subjects were randomly assigned to a creatine or placebo supplemented diet. All the subjects were measured be- fore and after loss of mass on both supplements for isokinetic peak torque (PT) and work at peak torque (W PT ) of knee extensors, also for intermittent high in- tensity working capacity of the same muscle group. The latter test consisted of submaximal isokinetic knee ex- tensions at an angular velocity of 1.57 rad á s )1 for 45 s at the rate of 30 contractions each min (submaximal work, W s max ) followed by 15-s maximal eort (maximal work, W max ). Total duration of the test was 3 min. Ha- ematocrit was measured and haemoglobin, ammonia, lactate, glucose and urea concentrations were analysed in blood samples obtained at rest and after cessation of muscle performance tests. The results indicated that creatine supplementation in comparison with placebo treatment during rapid body mass reduction may help to maintain muscle PT and W PT at high angular velocities, not in¯uencing W max and the rate of fatigue development during W max , but aecting adversely W s max . Within the limitations of the present study the reasons for the partially detrimental eect of creatine administration remain obscure, but it is suggested that impaired crea- tine uptake in muscle during body mass loss as well as creatine induced changes in muscle glucose and glycogen metabolism may be involved. Key words Intermittent intensity exercise á Ergogenic aids á Loss of body mass Introduction Athletes going in for sports with speci®c weight cate- gories such as wrestling, judo, karate, weight-lifting and some others often compete in a weight class below their usual body mass. Because of this, frequent cycles of rapid and extensive loss and regain of mass in these athletes have been reported to be common (Brownell et al. 1987; Steen and Brownell 1990). Athletes periodically lose mass believing their chances of competitive success will increase as a result. On the other hand, it is dicult to measure the in¯uence of the reduction of body mass on actual sports performance. At the same time several laboratory studies have re- vealed that loss of mass changes an athlete's metabolism and may decrease physical performance capacity (Houston et al. 1981; Kurachov et al. 1984; Horswill et al. 1990; Hickner et al. 1991; Maulli 1992; Rankin et al. 1996; O È oÈpik et al. 1996). It has been reported, how- ever, that some indices of working capacity may be maintained (Kurachov et al. 1984; McMurray et al. 1991) or even improved (Fogelholm et al. 1993) as a result of loss of mass. From a practical point of view, the most important issue is to ensure that the performance capacity of an athlete would be maximal not at the moment of weigh-in but just at the beginning of competition. In wrestling, for example, the athletes typically have 3±20 h to eat and drink ad libitum prior to their ®rst match. The compo- sition of the diet consumed at that time would therefore seem to be important. In the study of Rankin et al. (1996) they have shown that acute loss of mass via en- ergy restriction without dehydration impaired anaerobic performance in wrestlers. Performance tended to return to initial levels when the athletes were fed a 75% car- bohydrate diet over 5 h after loss of mass but did not recover when they ate a 47% carbohydrate diet. However, there are other sports like karate and judo, for example, where the competition usually begins very soon after the weighing of the participants. In these Eur J Appl Physiol (1998) 78: 83 ± 92 Ó Springer-Verlag 1998 Vahur O È oÈpik (&) á Mati PaÈaÈsuke á Saima Timpmann Luule Medijainen á Jaan Ereline á Tamara Smirnova University of Tartu, Institute of Exercise Biology, 18 U È likooli St., EE-2400, Tartu, Estonia