Eur J Appl Physiol (1999) 80: 165-168.
INTRODUCTION: During the last few years, athletes expecting to improve their physical performance have consumed dietary creatine supplements. The only documented secondary effect seems to be an increase of the body mass and more specifically of the fat free mass. This change in body composition could be explained in two ways. Firstly, the increase of free creatine concentration in the cells could induce water retention and thus modify the relative volume of the intra-cellular compartment. Secondly, creatine in itself, could induce muscle growth. The purpose of this study was to test these hypotheses.
METHODS: Twenty five healthy male subjects (age 22.0 ± 2.9 years; height 179.7 ± 5.2 cm) volunteered to participate in this experiment. The subjects were divided into three groups. Seven subjects formed the control-group. They did not complete any training and did not consume any dietary supplement neither creatine, nor placebo. The eighteen other subjects were randomly divided into a creatine- and placebo-group. They were submitted to a controlled strength-training program.
Body water compartments were assessed by bio-impedance spectroscopy using a BODYSTAT® DUALSCAN 2005 apparatus which was validated in a previous study (Hannan et al. 1995). A current was applied to the subjects at frequencies of 5 kHz and 200 kHz, successively, and the respective impedance values were recorded. A program supplied by the manufacturer of the analyser estimated the sizes of TBW, ECW and ICW from the impedance values.
Then the participants warmed-up before measuring the isokinetic force. At the end of the training programme, the body water content and the isokinetic force were measured. Then, the subjects were instructed to stop the strength training-program but to continue the ingestion of creatine during three weeks after which the body water content and the isokinetic force were determined again.
RESULTS: The control-group did not show any significant variation of the mean force developed during a single squat, while both the placebo- and creatine-groups increased by 6%. This indicates that creatine ingestion during a training period does not induce a higher increase in isokinetic force measured during a single movement. No change nor in body mass, neither in body composition was observed both in the control- and placbo-group during the entire experiment while the body mass of the creative-group incresed by 2.9%. In the latter group, the 200 kHz impedance value decreased indicating an extension of the total body water content. On the contrary, the 5 kHz impedance value did not change significantly rejecting any modification of the extra-cellular compartment. Thus, the origin of the total body water increase can be attributed to an enlargement of the intra-cellular volume. The magnitude of the TBW increase could explain the 55% of body mass gain and the 30% of the ICW enlargement.
DISCUSSION: Data from the literature do not indicate any change of total body mass during short-term creatine supplementation. Most previous studies and the present results showed that medium-term creatine supplementation increases total body mass by 1-2 kg. The values of TBW, ECW and ICW reported here are in good agreement with those presented elsewhere using a dilution technique. The creatine-group increaed the absolute value of TBW and ICW, but not the relative value, which indicates that the body mass gain folliwing a medium-term creatine supplementation is not due to intra-cellular water retention but probably to dry matter growth accompanied with a normal volume of intra-cellular water. These observations on intra-cellular water are in good agreement and extend prevous observations, showing a gain in total body mass after creatine supplementation without any change in the percentage of total body water. Different hypotheses can be formulated to explain the link between creatine supplementation and gain in dry matter.
To summarize, the major finding of our study is to emphasize, for the first time, that body mass gain observed after medium-term creatine supplementation is not due to water retention in the cell but probably to dry matter gain.