Influence d'une supplémentation en vitamines sur le rendement de la locomotion après une épreuve d'ultratrail

Aim. – The purpose of this study was to study changes in gross efficiency of locomotion after a prolonged trail running race (3000 m up and 300 m down). The second purpose was to investigate the effectiveness of supplementation in vitamin on gross efficiency variability.Materials and methods. – Twenty-two well-trained endurance runners took part in this study. They had to perform four sub maximal tests before, 24, 48 and 72 hours after the race in order to estimate gross efficiency of locomotion and a maximal contraction test in the same period. They were divided in two groups either with supplementation (Isoxan Endurance ^®) or without (placebo).Results. – In both groups we have observed a decrease in gross efficiency 24 and 48 hours after the race (respectively before and 24 hours after: 20.02 ± 0.2 vs 19.4 ± 0.1%, P < 0.05) and a decrease in Maximal Voluntary Force. Within this framework these alterations were significatively less important in the group with supplementation.Conclusion. – Results of this study confirm the classically observed decrease in efficiency during prolonged exercise. In our study supplementation in vitamin (according to the recommended daily allowances) are associated with a less important decrease in efficiency and maximal force suggesting a possible effect of supplementation on muscular function. Further works are necessary to validate this hypothesis especially after eccentric contractions.     

Effet de la posture sur le choix de la fréquence de pédalage préférée en montée

Purpose. – The aim of this work was to study the effect of the posture on the preferred pedalling frequency during uphill cycling.Methods and results. – Ten trained cyclists performed two pedalling trials of three minutes at 80% of maximal aerobic power on a treadmill with a slope of 4%. Two postures (seated and standing pedalling) were studied in a randomized order. During the first minute of each trial, the subjects had to choose their preferred pedalling frequency with adjusting their gear and then kept this rate until the end of the trial. The preferred pedalling frequency was significantly (P < 0.05) lower in standing (73 ± 7 rpm) than in seated pedalling (80 ± 9 rpm).Conclusion. – We suppose that cyclists choose a lower pedalling frequency during standing pedalling in order to generate greater peak pedal force and to decrease the number of lateral sways of bicycle and vertical elevations of pelvis, which increase energy cost.     

Variation de la fréquence cardiaque au cours du décathlon

Objective. – The goal of this study is to evaluate the cardiac activity during exercise and recovery throughout an intermittent event such as the decathlon.Methods. – Heart rate (HR) was recorded continuously (5 s interval) using cardiofrequencemeter in 6 athletes (age: 25.0 ± 3.7 years; weight: 72 ± 5.4 kg; height: 178 ± 9.1 cm) participating to a regional decathlon championship.Results. – The races are the most demanding on a cardiovascular point of view (HR: 170–200 beats/min (bpm)). They are followed by the jumps (HR: 140–170 bpm) and the throws (HR: 110–140 bpm). Between each event, HR progressively decreases as a sign of recovery period. During the throws and the jumps, HR drops between each attempt but this drop is blunted during the pole vault and the high jump events, revealing a more intense state of stress. The night period is important for the cardiovascular recovery with a stability of HR during sleep.     

Influence du cycle menstruel ou de la prise d'un contraceptif oral sur la performance lors de l'épreuve de Wingate

Objective. – Evaluate the performance during a Wingate test in 14 non-training young women with (CO+) or without oral contraceptives (CO–) at the beginning and the end of menstrual cycle.Methods and results. – During a Wingate test, the power peak (PP), the mean power (PME), as the fatigue index (IF) and lactate concentration do not differ significantly according to the period from the cycle (j5–j9 and j19–j27) and the studing group. Compared with the group CO–, the women CO + are bigger with an upper lean mass and develop a greater PME, but this difference disappears from the moment when PME is reported to the weight in kilogram or to the lean mass.Conclusion. – These results suggest that the hormonal cycle or the grip of an oral contraceptive do not affect the measured performance during a test of Wingate.     

La fracture de fatigue : facteurs de risque et perspectives d'identification

Aim. – The purpose of this paper is to give an overview on the scientific information related to stress fracture risk factors and to present the recent contribution of bone microarchitecture analysis in this field.Current knowledge. – Stress fractures are common overuse injuries sustained by athletes and military recruits and cause considerable interference with training. Although several risk factors have been comprehensively assessed in numerous studies, no consensus emerged. Hence, to date, there is still no general screening tool available to identify individuals at risk.Prospects. – Stress fracture prevention requires identification of particular bone characteristics that predispose to this injury. Bone texture analysis, identifying microarchitectural properties, seems to offer new prospects in the identification of stress fracture susceptibility. A recent study revealed that the bone texture indicator Hmean is lower in stress fracture cases than in controls (0.7651 ± 0.027 vs 0.7877 ± 0.016; P < 0.005).     

Relation entre la puissance maximale anaérobie mesurée lors de l'épreuve charge–vitesse,la détente verticale et le 5-jump test chez le garçon entraîné

Purpose. – The aim of this study was to investigate the relationship between maximal anaerobic power measured by force-velocity test and performances in vertical jump and in 5-jump test in young boys.Methods. – 18 trained boys participated in this study (mean age 12 ± 0.4 years). They performed three anaerobic tests: force-velocity test, vertical jump test and 5-jump test. Anthropometric measurements were made to estimate the muscle volume of the lower limbs. Peak anaerobic power (Watts, Watts/kg and Watts/l of muscle) was measured during a force-velocity test on a Monark ergocycle. Performances were measured during vertical jump test with a force platform and during the 5-jump test.Results. – We found a significant correlation between the peak anaerobic power measured during force-velocity test (W) and body mass (r = 0,80; P < 0,001). The peak power (W, W/kg) was also correlated to muscle volume (r = 0.89; P < 0.001; r = 0.63; P < 0.01 respectively). Furthermore, peak anaerobic power (W/kg) was significantly correlated with performance in vertical jump (r = 0.64; P < 0.01) and with the 5-jump test (r = 0.74; P < 0.001). Vertical jump was also correlated to the 5-jump test (r = 0.63; P < 0.01).Conclusion. – This study shows significant correlations between peak anaerobic power, body mass and muscle volume in trained young boys. Furthermore, correlations observed between the Force-velocity test and performances in both vertical jump and the 5-jump test suggest that the 5-jump test is a good tool to estimate muscular anaerobic power of legs and a very practical means of selection and/or orientation of young people to explosive sports.     

L'IGF-1 induit une augmentation de la taille et du contenu en myosine des myotubes humains

Introduction. – In this study, we tested the ability of IGF-1 (insulin-like growth factor-1) to increase the size of human myotubes in culture.Synthèse des faits. – IGF-1 treatment induces hypertrophy of human myotubes characterized by a dose dependant increase in the mean number of nuclei per myotube, in the size of the myotubes and a significant increase of 96,4 ± 50,48% (P = 0,002) of the ratio myosin/émerine.Conclusion. – In this study, we showed that IGF-1 induces an increase in the size of human myotubes in culture and increases myosin synthesis, thus mimicking the hypertrophy described in vivo. This model will be used for further analysis of the molecular mechanisms involved in this hypertrophy.     

Intensité de l'activité et récupération post-match chez l'arbitre de rugby

Objective. – To evaluate the impact of a rugby match in term of energetic demand and the post-match recovery during the days following a rugby match in national level referees.Results and discussion. – A rugby match corresponds to an intense aerobic activity, with a total distance covered of 7,532 ±1,081 km and a mean heart rate 160 ±11 in 35 ±4 years aged referees. During the match, the salivary cortisol level rises to 3 fold pre match level, showing a high physiological constraint. During the five following days, awakening cortisol levels were similar to basal one, meaning that this activity does not induce recovery difficulties in the subjects of this study.     

Validation du système Optojump en tant qu'outil d'évaluation de la force-vitesse (puissance) des membres inférieurs

Purpose. – The aim of this study was to examine Optojump system efficiency to analyse lower limbs explosive strength.Methods and results. – Twenty untrained subjects were randomly assigned to 2 groups: either an experimental group (N =10) or a control group (N =10). They performed vertical jumps using different techniques and sprints. Reproducibility of jumps and sprint, evaluated by Optojump system, was appreciated after correlation analysis . The experimental group took part in a plyometric training for six weeks. Jumps and sprints showed an excellent reproducibility (mean coefficiant of variation =3.6%). Plyometric training increased (P <0.001) counter movement jump (+19.6%), counter movement jump free arms (+14%) and drop jump (+27.9%) performances.Conclusion. – This study demonstrated the accuracy and validity of the Optojump system to analyse lower limbs explosive strength.     

Créatine,exercice et synthèse protéique musculaire

Aims. – To evaluate the effects of creatine supplementation on the metabolism protidic during the exercise.Materials and methods. – Seven young healthy men performed on two occasions 20 × 10 repetitions of one leg extension-flexion at 75% one-repetition maximum, the resting leg being the control. Before one of the two experiments, the subject ingested creatine (21 g per day for 5 days). The subjects ate 21 g maltodextrin + 6 g protein per h for 3 h postexercise period. The subjects were perfused with [1-¹³C]-leucine and [2H5]-phénylalanine. Biopsy samples were taken from the vastus lateralis and arterial and venous blood samples were drawn. Proteins synthesis and breakdown were calculated for the rested and exercised leg. Creatine supplementation increased muscle total creatine by about 21% (p < 0.01). Exercise increased the synthetic rates of myofibrillar and sarcoplasmic proteins by two- to three-fold (p < 0.05) and the leg phenylalanine balance became more positive, but creatine was without any anabolic effect.     

Adolescents sportifs,offre et demande de substances pour améliorer la performance

Introduction. – Little is known about the main methods and means employed to supply adolescents with doping agents and others substances used to improve their sporting performance.Main facts. – A study in France among all the adolescent of the ‘Union nationale du sport scolaire’, using a self-completed questionnaire, furnished 6402 exploitable questionnaires, corresponding to 48.9% for the girls and 51.1% for the boys, both aged on average from 16.1 ± 2.2 years. These adolescents practise on average 10.0 ± 5.2 hours of sport per week. 21.9% participate on a national or international competition level. Of our respondents, 4.0% said they had been enticed into using products, which are prohibited for athletes. 10.3% of the adolescents stated that they had received substances to improve their performance at least once from an average of two different people. It was mostly a friend, their parents and the family doctor. In nearly half the cases (46.6%), the adolescent paid for the product.Conclusion. – It is necessary to better understand the ways in which this black market functions: for example; the initial sources of the products sold, the number and the ‘profiles’ of the dealers, the general organisation of the market and the sums of money involved.     

Plongée à l'air avec la table de décompression MN 90. Bilan de 12 années d'utilisation par la Marine française : à propos de 61 accidents de désaturation de 1990 à 2002

Objective. – Decompression MN 90 Table is used for air diving by military divers and both sports divers in France. In the aim to confirm MN 90 safety, we studied 61 decompression sicknesses observed in the French Navy for 1990–2002.Method. – Each year 1800 divers carry out 150 000 dives ± 10%. Divers are 1600 ship divers (dives less than 35 m-sub-water) and 200 mine clearance divers (dives up to 60 msw max). Each accident must be notified and data are recorded into a database.Results. – The total risk is estimated at 1 accident/30 000 dives. We observed no death and only 2 divers with persistent neurological deficits. We found spinal decompression sickness: 66%, cerebral 23%, inner ear 8% and joint bends 3%. Neurological accidents are purely sensitive for 65%. The evolution was favourable for 97% after early hyperbaric recompression at 400 kPa. One hundred percent respected the MN90 procedure. Water temperature, age, effort during diving, repetitive dive were not found as risk factors. A right-to-left shunt was present for only 30% of type II accident. The main result of the study is that 54% of accidents concerned only 200 mine clearance divers with a risk estimated at 1 accident/3000 dives for 45–60 msw depths.Conclusion. – MN90 decompression procedure is safe for a young population of trained military divers with a low risk of accident. The major risk factor seems to be the depth. Studies are necessary to optimize the decompression for deep air diving.     

Relation entre la force isocinétique,le saut et le sprint chez le footballeur de haut niveau

Purpose – The aim of this study is to appreciate the relation between sprint, jump and knee isokinetic torque in high-level soccer players.Methods – Twenty soccer players (first french national division) were evaluated by sprint and jump tests. Extensors and flexors isokinetic torque was measured by a Cybex Norm dynamometer. Relations between sprints, jumps and isokinetic peak torque were appreciated after correlation analysis.Results – Jumps are correlated with the extensors concentric peak torque at the speed of 180° s⁻¹ when values were corrected by weight (Squat Jump: r = 0.507; Countermovement Jump: r = 0.649; Vertical Jump: r = 0.496). Sprints are correlated with the extensors concentric peak torque at the speed of 180° s⁻¹ when values were corrected by weight (10 and 20 m fixed departure sprint: r = −0.427 and −0.548; 10 and 20 m thrown departure sprint: r = −0.406 and −0.480). Furthermore, sprints with fixed departure are conversely correlated with the flexors eccentric peak torque at the speed of 60° s⁻¹ (r = 0.546 and 0.478) doubtless because a mechanism of knees protection.Conclusions – According to these causal relations, knee extensors and flexors strengthening is recommended for high-level soccer players with the aim of improving sprints and jumps.     

Rugby practice and skeleton: correlations between strength,bone mineral density,and biochemical markers of bone remodeling

Aim. – To investigate the relationships among muscular strength, bone mineral density (BMD) and biochemical markers of bone remodeling in healthy active male rugby players.Materials and methods. – BMD was measured by dual-energy X-ray absorptiometry. Bone formation was assessed by measurements of circulating osteocalcin (OC). Bone resorption was assessed by urinary levels of cross-linked C-telopeptides of type I collagen (CTX).Synthesis. – Positive significant correlations (P < 0.05 to P < 0.0001) were shown between strength and total and regional (spine, pelvis, and legs which are specifically stressed by this sport participating) BMD. In the same way, the OC, but not CTX, is highly correlated with the same regional and total BMD.Conclusion. – The correlation reported between the BMD and the bone osteogenic marker OC, implies that this positive bone adaptation may be linked to an improvement of the bone remodeling speed.     

Pratique sportive et conduite dopante d'un échantillon représentatif des élèves de Midi-Pyrénées

Objective – Estimate the phenomenon of doping in sport among french adolescents.Method – Our effective population was the students of the Midi-Pyrenees French Region in 1999 exception made of the high-level sport section. The data were gathered by an anonymous questionnaire filled by a representative sample of 1 506 girls and 1 420 boys aged from 13 to 20 randomly selected by a two stage sampling. Regionals estimations are given.Results – A sport-practice out of school concerned 85% of our sample. Nearly 3 000 students of our effective population (2% of this population) would consume a substance classified as a doping-drug for sport (sometimes innocently), and 8.6% of our athletes would consider to know a « friend consumming doping substances for sport-practice». The situation would be more worrying if we consider that more than 12 000 adolescents (8.7%) of the effective population would be tempted to consum suc a substance. The most cited doping substances were caffeine shape of tablet, beta 2 mimetics and cannabis. A total of nine students also declared a creatine consumption.     

Apports et statut en vitamines antioxydantes chez des athlètes d'endurance

Introduction. – This study compares the antioxidant vitamin intakes of endurance athletes engaged in an extreme running competition to the recommended dietary allowances. The daily energy intake and the macronutrients distribution have been also measured.Synthesis of facts. – The intake of vitamin E is insufficient for 95% of the athletes and 22% of them have a low intake of vitamin C, β-carotene and retinol equivalent. The total energy intake is also low (145.4 ± 10.6 kJ/kg per day).Conclusion. – The athletes of our study did not have a sufficient intake of antioxidant vitamins that could be partially explained by a low total energy intake.     

Concurrent validity of the ActiGraph GT3X+ and activPAL for assessing sedentary behaviour in 2–3-year-old children under free-living conditions

ObjectivesActiGraph accelerometer cut-points are commonly used to classify sedentary behaviour (SB) in young children. However, they vary from 5counts/5 s to 301counts/15 s, resulting in different estimates and inconsistent findings. The aim was to examine the concurrent validity of ActiGraph GT3X + cut-points against the activPAL for measuring SB in 2–3-year-olds during free-living conditions.DesignObservational validation-study.MethodsSixty children were fitted with the activPAL and ActiGraph simultaneously for at least 2 h. Nine ActiGraph cut-points ranging from 60 to 1488 counts per minute were used to derive SB. Bland & Altman plots and equivalent tests were performed to assess agreement between methods.ResultsEstimates of SB according to the different ActiGraph cut-points were not within the activPAL ±10% equivalent interval (-4.05; 4.05%). The ActiGraph cut-points that showed the lower bias were 48counts/15 s (equivalence lower limit: p =  0.597; equivalence upper limit: p < 0.001; bias: -4.46%; limits of agreement [LoA]: -21.07 to 30.00%) and 5counts/5s (equivalence lower limit: p < 0.001; equivalence upper limit: p =  0.737; bias: -5.11%; LoA: 30.43 to 20.20%). For the 25counts/15s, 37counts/15s and 48counts/15s ActiGraph cut-points, the upper limits were within the equivalent interval (p < 0.001) but not the lower limits (p > 0.05). When using the 5counts/5s and 181counts/15s ActiGraph cut-points, lower limits were within the equivalent interval (p < 0.001) but not the upper limits (p > 0.05). Confidence intervals of the remaining ActiGraph cut-points lie outside the equivalent interval.ConclusionsAlthough none of the ActiGraph cut-points provided estimates of SB that were equivalent to activPAL; estimates from 48counts/15 s and 5counts/5 s displayed the smallest mean bias (˜5%).     

Effet de l'instruction sur la régulation de la raideur des membres inférieurs lors de sauts de contre-haut

Goal. – We tested in this study the possibility of influencing leg stiffness through instructions on the knee flexion in drop jump (30 and 60 cm).Method. – Twelve basket players were instructed to jump with three different instructions: 1) “jump as high as you can”; 2) jump high with a larger knee flexion at touch-down and 3) jump high with a smaller knee flexion at touch-down. The ground reaction force were measured with an AMTI force plate (500 Hz). The kinematics of the jump was recorded using two digital cameras (50 Hz).Results. – The results show that the ground reaction force pattern depended more on the instruction than on the height of the box. The active peak decreased from 6 times the body weight (BW) to 2.9 times BW. Bending the knee appears to be an efficient strategy to increase the leg stiffness [R =0.86; P <0.05].Conclusion. – The instructions high knee flexion decreases the leg stiffness. The same vertical jump performance could be achieved with different values of stiffness. The maximum knee flexion does not modify the vertical performance.     

Les records de profondeur en plongée libre : réflexions d'un physiologiste

Object – to study the progression of breath-hold depth records, and to find the factors of improvement, with the help of statistical methods.Results – in the “no limits” class, the depth of records as a function of time can be alined about a straigth line, with a regular slope (2.26 m year⁻¹), but close to the “psycological depth” of 100 m. The improving of the “no limits” records fit with an increase of the mean speed from 0.9 m s⁻¹ in 1976 (no previous figure) to more than 1.5 m s⁻¹ in 1999, due to the change of the diving position head up when going down, to the position head first in every case, going down or going up; the improvement results also in a better shaping of the weigh-brake-buoy kit. We subjected these facts to statistical analysis:

• •the study checks that the depth/time relation can be represented by a straight line with an error of 14%; a graph based on a curvilinear regression of exponential form with periodicity meet better (standard deviation: 0.052); the differential ratio from the logarithmic function is then 1.7%;
• •the speed/time diagram shows a good correlation; its slope points out a speed increasing by 2.83 cm year⁻¹;
• •the analysis of variance upon the quantitative variable depth with two factors (nationality, level of number of records) leads to hightly significant results, with a small residual.

A critical study of the factors restricting the depth of breath-hold records suggests the maximal depth is not yet reached; the limits appear to be still remote.     

Influence du tabagisme et du niveau de dépendance nicotinique sur l'endurance musculaire chez des sujets entraînés

Aim. – To evaluate the influence of tobacco smoking on muscular endurance according to the degree of nicotinic dependence among trained subjects.Methods and results. – Two groups of trained male students were tested. The first group consisted of 120 smokers, and the second of 126 non-smokers. All the subjects belonged to second division of Congolese football league clubs. Degree of nicotinic dependence was evaluated by Fageström test. Anthropometrics characteristics (height, weight, lean body mass) were evaluated before the test of evaluation of muscular dependence. Significant falls (P <0,05) of all the components of muscular endurance were observed among the smokers, compared to non-smokers. Beside, the degree of nicotinic dependence had an effect on these limitations, for two components out of three (P <0,001).Conclusion. – This study demonstrates that tobacco smoking leads an alteration in the muscular endurance capacities of sportsmen.