Les effets indésirables de la créatine exogène: de la fiction à la réalité

Summary

Objectives

For the last six years the consumption of exogenous creatine monohydrate has been extended more and more. Despite numerous publications on the ergogenic effects of this naturally occurring substance, there is almost no information on the deleterious effects of this supplement. The objectives of this review are to point out facts which are often in contradiction with allegations introduced by the media.

Topics

In athletes, exogenous creatine supplements amount to 20 g per day during five days followed by 1 to 10 g per day, every day, for weeks, months, and even years. Usually consumers do not report side-effects, with the exception of body weight increase. However, gastro-intestinal disturbances and muscle cramps have been reported occasionally. Liver and kidney dysfunction have also been hypothesized but real facts are missing for this. From a theoretical point of view, exogenous creatine supplementation suppresses its hepatic synthesis (maximum 2 g per day for vegetarians). Its destination is mainly (95–98%) skeletal muscle and all excess is excreted in urine (on average 60% of the supplement). Scientific publications on the undesirable effects of exogenous creatine are almost non-existent, but newspapers and the media do not hesitate to publish false information or wrong interpretations based on one individual case of an individual with nephropathy who, later on, consumed creatine monohydrate. In addition, we did not find any side-effects on renal function after short-term (five days), medium-term (nine weeks) or long-term (up to five years) creatine supplementation in small cohorts of athletes.

Future prospects

We have no intention to validate or not the supplementation of exogenous creatine by athletes, but apparently there are no real deleterious effects on the body of healthy consumers. Nevertheless, one has to be careful about individual reactions when excess food are taken up. We are convinced that regular biological check-ups are needed to avoid any abnormal reaction under creatine supplementation.     

Le questionnaire de surentraînement de la Société française de médecine du sport : reproductibilité à court termeOvertraining questionnaire of the Société française de médecine du sport (French Society of Sport Medicine): short term reproducibility

Purpose. – To assess the short-term stability, over time, of a slightly modified version of the overtraining questionnaire proposed by the SFMS.Methods. – Three or 7-day test–retest of the questionnaire was completed in 30 high level athletes. In a first stage analysis, the score obtained during the first test was compared to and correlated with that obtained during the second one. Then, in a second stage analysis, the individual reproducibility of each item was assessed using a similitude index: a value of 100% meant that all the athletes gave an identical response for the two trials.Results. – Scores were not different between the two tests and intra-class correlation coefficients were r = 0.82. Overall reproducibility of the similitude index was quite good even if six items of 52 displayed a lower similitude index (around 80%).Conclusion. – The short-term reproducibility of the overtraining questionnaire is quite good. This result reinforces its reliability and warrants its use in a longitudinal follow-up framework aimed to detect precociously an overtraining syndrome.     

Effets en miroir de l''entraînement et du surentraînement sur la fonction somatotrope et la balance glucidolipidique à l''exerciceEffects out of mirror of the drive and overtraining on the somatotropic function and the glucido-lipidic balance with the exercise

Objective. – To confirm the assumption whereby overtraining would have opposite effects on the utilisation of the substrates and the somatotropic function.Exposed facts. – The drive has different effects according to its characteristics and its level. It seems y to have two types of drive: that which amplify the aptitude to oxidize lipids (low powers) and that which accroit the aptitude to oxidize glucides (high powers and/or intermittent exercise). Overtraining reverses these two effects. The somatotropic axis has an evolution parallel with these processes and seems implied in those.Conclusion. – This diagram deserves to be confirmed by additional studies.     

Intérêt du questionnaire de surentraînement de la Société française de médecine du sport lors d’un suivi de sportifsOvertraining questionnaire of Société française de médecine du sport for a continuous observation in a sport population

Aim. – Verify the sensibility of a standardised overtraining questionnaire during a weekly observation in a sport population.Methods and results. – The experiment was carried out in 12 athletes, 20–23 years old, students at the University in Licence STAPS, with a standardised overtraining questionnaire given every week during 8 weeks. Results were analysed individually and for the total population. Those showed that overtraining questionnaire could allow individualised training programs, and could provide some pertinent information on sleep quality and physical condition for each athlete. For the coach, the overtraining questionnaire permits to identify some fatigue state, consecutively to training variations. On the total population, the analysis of overtraining questionnaire showed some items more reliable than other.Conclusion. – This questionnaire was very interesting for coaches, allowing a good individualisation of the training program. Nevertheless, this questionnaire presents intricate statistical analysis when given at high frequency.     

Influence des paramètres anthropométriques sur la performance en aviron au niveau national

Introduction. – L'objectif de cette étude est d'observer l'influence des paramètres anthropométriques sur la performance en aviron, chez des rameurs de niveau national et international.Synthèse des faits. – Les mesures anthropométriques ont été réalisées sur 88 rameurs (dont 11 évoluant au niveau international) lors des championnats de France de 2002. Ces mesures ont été corrélées aux performances réalisées sur ergomètre et en bateau. Des différences significatives sont mises en évidence entre les caractéristiques anthropométriques des rameurs de niveau national et international. Ces caractéristiques semblent être reliées directement aux performances ergométriques et non à celles réalisées en bateau.Conclusion. – L'influence des caractéristiques anthropométriques sur la performance en aviron pourrait être modifiée en fonction des niveaux de compétition.Aim. – Observe the influence of anthropometrics characteristics on rowing performance, at national and international level.Results. – Anthropometrics measurements of 88 rowers (included 11 international rowers) were realized during the national championships, data were correlated to ergometer and boat performances. Significant differences appear between anthropometrics characteristics of national and international rowers. Anthropometrics parameters seem related to ergometer performance but not to boat performances.Conclusion. – The influence of anthropometrics characteristics on rowing performance could be modified by the competitive level.     

Fécondité féminine et activité physique intense et répétéeFemale fertility and intensive physical activity

Aims – To estimate the effects of intensive physical activity on female fertility.Current knowledge – Since twenty to thirty years ago, women have regularly participated in intense physical sports. The first Olympic Marathon for women took place at Los Angeles (United-States) in 1984 and many clinical studies concerning the incidence of menstrual disturbances among sportswomen, were concomitant of the dramatic increase in female participation in endurance sports, either as recreational or professional sportswomen. Most of these studies were focused on secondary amenorrhea. Later, etiological studies have shown that a range of disturbances, from an apparently normal menstrual cycle, irregular menstruation, oligomenorrhea to the complete blockage of the ovarian function were observed.Points of views and plans – It is very likely that the physiological process leading to menstrual troubles among sportswomen include disturbances of GnRH pulsatility at hypothalamic level. It has been shown that a session of training at an intensity greater than 60% during at least 40 min leads to the secretion of neuromediators able to interfere with GnRH pulsatility. Repetitiveness of daily sessions of training (i.e., more than five sessions a week) associated with marginal energy intake or strictly vegetarian food may contribute to disturb the hypothalamo-pituitary-ovarian axis in female athletes.     

Composante lente de VO2 chez l''enfant prépubère lors d''exercices rectangulaires d''intensité élevéeThe slow component of VO2 uptake kinetics during high-intensity exercise in prepubertal children

Aim – The aim of the present study was to investigate the VO2 uptake slow component in prepubertal children of different aerobic capacity during high intensity exercise.Method – Twenty three (12 well-trained and 11 untrained) prepubertal children took part in two constant-power tests performed at intensities corresponding to 80% of the anaerobic threshold and 90% of maximal aerobic power. VO2 kinetics during both constant-power tests was determine using a monoexponential + linear term model.Results/conclusion – Our results demonstrated the existence of a slow component during heavy intensity exercise in prepubertal children, as previously described in adults. The magnitude of this slow component did not differ between trained swimmers and untrained children exercising at the same relative intensity, provided that the whole VO2 response was considered.     

L''hémorhéologie permet-elle de comprendre le « paradoxe de l''hématocrite » lors de l’entraînement et du surentraînement ?Does hemorheology explain the paradox of hematocrit in training and overtraining?

Purpose. – Doping with EPO increases both hematocrit and performance. On the opposite, training reduces hematocrit due to plasma volume extension and overtraining both increases hematocrit and decreases performance. This apparent paradox seems to be explained by a new concept proposed interpreting the interactions between viscosity factors and blood flow.Facts. – Viscosity factors exert a non linear “all or none” effect that can be described according to the “ percolation theory”. Blood viscosity has no hemodynamic relevance by its own, but viscosity factors (hematocrit, red cell deformability and aggregability, plasma viscosity) can result according to flow conditions in self-potentiating phenomena of quick transition between a state of high fluidity and a state of red cell aggregate clumping. In muscle, this model predicts that: (a) during exercise the only viscosity factor that could influence flow is plasma viscosity; (b) at rest all viscosity factors (including high hematocrit) may induce a self-potentiating “viscidation” process.Conclusion. – According to these concepts, supraphysiologic hematocrit values are probably unable to disturb muscular perfusion at exercise, but are likely to promote self-potentiated stasis at rest and thus to increase the risk of thrombosis.     

Activité physique et remodelage osseux : étude chez une population de jeunes gymnastesPhysical exercise and bone turnover: a study in young girl gymnasts

Aims – Intensive exercise is known to improve the bone mass acquisition. One of the main explanations consists in the mechanical strains exerted on the skeleton. Little is known about the effects of physical exercise on the bone remodelling process.Methods and results – The bone remodelling rate evaluated in a group of young female (24 gymnasts and 21 controls), using a bone resorption marker, the CrossLaps peptides CTx. We measured in our subjects the bone mineral density at the whole body and at six regional sites. The bone density was statistically higher in the gymnasts compared to the controls at all the specific sites. The CTx level corrected by urinary creatinine was significantly higher in the gymnasts, reflecting a faster bone remodelling rate.Conclusion – Intensive physical activity could improve the bone mineral acquisition probably by a stimulation of the bone remodelling activity.     

Influence de l''hydratation sur la sécrétion d''hormone de croissance induite par l''exerciceHydration influence on exercise-induced growth hormone secretion

Aim – Study was then to investigate hydration influence on exercise-induced GHh secretion.Methods and results – Seven healthy men underwent a submaximal rectangular cycling exercise for 30 minutes to 150 watts during two sessions. A first one without any water intake and a second one with ingestion of spring water corresponding to the volume of water lost during the first session. Plasma volume decrease was significantly higher during the first session (p < 0.05). Total GH secretion was significantly lower during this session (p < 0.05).Conclusion – A moderate dehydration decreases exercise-induced GH response. Thus, hypovolemia may exert a negative feed back on GH secretion, during exercise.     

Effets du repas précompétitif sur la perception de l'effort et sur la glycémie lors d'un exercice de pédalage

The first purpose of the present study was to investigate the effect of three different preexercise meals on perceived exertion and glycaemia during a one-hour bicycle exercise at 80% VO₂ max. The second purpose of this study was to determine the relationship between glycaemia and perceived exertion. Eight athletes (age: 24.6 ± 2.7 years, weight: 78.0 ±6.8 kg, height: 182.6 ± 9.9 cm) completed three assessment sessions, each being preceeded by one of the following meals, ingested 3 h before exercise: 400 mL of water, 400 mL of water and 75 g of glucose, and 100 mL of water and 375 g of potatoes. The subjects 'perceived exertion were measured at times 6, 15, 30, 45, 60 min and glycaemia at 0, 30, 60 min of the exercise. The results showed that perceived exertion (RPE and ETL) of each meal increased as a function of time (P <- 0.05) whereas glycaemia did not differ except for the glucose meal between 30 min and 1 h(P < 0.02). There was no significant difference in ratings of perceived exertion among any meal whereas glycaemia was different between the three conditions only at the beginning and the middle of the exercises (P < 0.04 and P < 0.02, respectively). Moreover, the vectorial angles between the variables ofperceived exertion and the glycaemia are close to 90 °. These results would suggest that perceived exertion does not seem to be affected by the three preexercise meals used in our study. Perceived exertion is not correlated to glycaemia changes during one-hour high intensity exercise. The results would, therefore, suggest that glycaemia is not a contributor signal of perceived exertion in this study. It seems that physiological factors other than glycaemia may have mediated the perceptual intensity at exhaustion. The respiratory-metabolic signals of exertion which are most pronounced at high relative exercise intensity are suggested to influence the perceptual signal of exertion.     

Suivi de l’entraînement de nageurs de haut niveau par questionnaire de fatigue, dosages hormonaux et variabilité de la fréquence cardiaqueTraining follow up by questionnaire fatigue, hormones and heart rate variability measurements

Introduction. – A short questionnaire of fatigue, urinary cortisol/cortisone ratio and heart rate variability were measured in 14 elite swimmers during heavy, light and moderate training periods.Results. – The questionnaire was strongly related to the variations of training and performance (r > 0.70). Correlations were lower with the hormonal ratio and insignificant with the heart rate variability.Conclusion. – The questionnaire and the hormonal ratio were good markers of the variations of training and performance contrary to the heart rate variability.     

Adaptations mécaniques et neurophysiologiques induites par la sollicitation musculaire excentrique : l''effet protecteur

Objectifs. – Présenter la notion d'effet protecteur induit par la sollicitation musculaire excentrique et aborder les différents types d'adaptations pouvant rendre compte de ce phénomène.Actualités. – La réponse du complexe neuromusculaire à une séance de renforcement musculaire excentrique est conditionnée par le type de sollicitation réalisée au préalable. Les dommages musculaires sont en effet moins marqués et la récupération de la contractilité musculaire plus rapide si des sollicitations excentriques sont effectuées quelques jours à plusieurs mois avant la séance.Conclusion. – L'effet protecteur semble préférentiellement résulter d'une adaptation du tissu contractile à la contrainte mécanique. La prise en compte de l'effet protecteur doit permettre d'optimiser la programmation de l'entraînement de la force et de la rééducation fonctionnelle.Objectives. – To present the eccentric contraction-induced protective effect, as well as the different kind of adaptations possibly involved in this phenomenon.Topics. – The effects of an eccentric exercise session on the neuromuscular system depend on the contraction type performed previously. A repeated eccentric exercise does not induce the same negative effects on force production capacity than a first bout. Indeed, strength recovery is improved and eccentric exercise-induced ultrastructural damages are less pronounced after a second exercise bout performed 5 days to 6 months after the first one.Conclusion. – The protective effect seems to be mainly related to contractile adaptations to eccentric muscular solicitation. Strength training and rehabilitation programs could be improved by taking into account this protective effect.     

Effets de l'entraînement sur les potentiels aérobie et anaérobie de jeunes nageurs. Exercice réalisé avec les brasEffect of training on aerobic and anaerobic capacity in young swimmers. Exercise performed with arms

Aims – Investigate the influence of exercise training on the aerobic and anaerobic capacities of young swimmers.Methods – Ten male swimmers aged 15.2 ± 3.8 years participated: five sprint specialists and five middle-distance specialists. Each subject performed, an arm ergocycle, two laboratory tests, a maximal incremental exercise test and a force–velocity test, once in February (T1) and then again in June (T2).Results – For all subjects combined (n=10), the results showed a significant increase in maximal anaerobic power (p < 0.01) between T1 and T2. Aerobic capacity did not change significantly between the two tests in either group.Conclusion – This study demonstrates the interest of evaluating aerobic and anaerobic capacity in young swimmers during arm exercise. The change in results over the 5-month period between the two tests indicates the importance of scheduling exercise tests during the course of athletic training programs.     

Taux sériques du propeptide aminoterminal du procollagène III chez des sportifs soumis à un entraînement régulier

Serum Procollagen III N-terminal Propeptide (PIIINP), a marker of bone matrix turnover, was measured in 36 sportsmen undergoing intensive training, including 23 adolescent gymnasts. All values are within the range of control values for age, suggesting that PIIINP is not modified by intensive training.     

Le « syndrome des jambes lourdes » chez les athlètes surentraînés est-il le reflet de désordres hémorhéologiques ?Is the feeling of heavy legs in overtrained athletes related to impaired hemorheology?

Introduction. – The aim of this work is to evaluate if the feeling of heavy legs in athletes is correlated with overtraining syndrome-related hemorheological disturbances.Results. – The subjects who quoted the item: “I have the feeling of heavy legs” had higher plasma viscosity and higher red cell aggregation parameters. The overtraining score was correlated positively with plasma viscosity, and aggregability parameters. The feeling of heavy legs was correlated with plasma viscosity and aggregability.Conclusion. – These findings suggest that the feeling of heavy legs in overtrained athletes is related to overtraining syndrome-related hemorheologic disturbances, namely mild plasma hyperviscosity and mild erythrocyte hyperaggregability.