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Biomedical subjects

G Cometti

Publications and source records attributed to G Cometti.

16 recordsLinked to original sources
PubMed2001

Isokinetic strength and anaerobic power of elite, subelite and amateur French soccer players.

Information about the influence of different practice levels on physical characteristics of a large number of soccer players is lacking. Therefore we assessed muscular strength and anaerobic power of elite, subelite and amateur soccer players to clarify what parameters distinguish the top players from the less successful. We tested 95 soccer players from the French first division (elite), second division (subelite), and amateurs and determined the isokinetic strength of the knee extensor and flexor muscles at angular velocities from -120 degrees x s(-1) to 300 degrees x s(-1). Vertical jump, 10 m sprint, 30 m sprint and maximum ball speed during shooting were also measured. The elite players had higher knee flexor torque than the amateurs at all angular velocities (p < 0.05), except at 300 degrees x s(-1). The hamstring/quadriceps ratios proposed with two different methods were significantly lower in the amateur group than in the elite group (p < 0.05), except at 300 degrees x s(-1). Maximum ball speed during shooting and speed over 30 m sprint were not different between elite, subelite, and amateur players while speed over a 10 m sprint was significantly slower in amateur players and faster in the elite group (p < 0.05). Although performance in soccer is not determined only by measurable variables, professional players differ from amateurs in terms of knee flexor muscle strength and short-distance sprinting speed. Based on these findings we conclude that hamstring strength is extremely important in soccer players for joint stabilization during various tasks, notably in eccentric action. Further, short-sprinting performance may mirror actual game situations at high level and could be an important determinant of match-winning actions.

Adult↗
PubMed2000

The effects of electromyostimulation training and basketball practice on muscle strength and jumping ability.

The aim of this study was to investigate the influence of a 4-week electromyostimulation training program on the strength of the knee extensors and the vertical jump performance of 10 basketball players. Electromyostimulation sessions were carried out 3 times weekly; each session consisted of 48 contractions. Testing was carried out before and after the electromyostimulation training program (week 4) and once more after 4 weeks of normal basketball training (week 8). At week 4, isokinetic strength increased significantly (p < 0.05) at eccentric and high concentric velocities (between 180 and 360 x s(-1)); this was not the case for low concentric velocities (60 and 120 degrees x s(-1)). Electromyostimulation training increased also isometric strength at the two angles adjacent to the training angle (p < 0.01). Squat jump increased significantly by 14% at week 4 (p < 0.01), whereas counter movement-jump showed no change. At week 8, gains in isokinetic, isometric strength and squat-jump performance were maintained and the counter movement jump performance increased significantly by 17% (p<0.01). Electromyostimulation as part of a short strength-training program enhanced knee extensor strength and squat jump performance of basketball players.

Adult↗
PubMed1999

Velocity-specific training in elbow flexors.

The purpose of this study was to show that velocity-specific training may be implicated in modifications in the level of coactivation of agonist and antagonist muscles. Healthy males (n = 20) were randomly placed in to two groups: one group trained using concentric contractions (n = 12), the other was an untrained control group (n = 8). The training group underwent unilateral resistance training at a level of 35 (5)% of a one-repetition maximal contraction of the elbow flexors, executed at maximal angular velocity. Training sessions consisted of six sets of eight consecutive elbow flexions, three times per weak for a total of seven weeks. The velocity of the ballistic movements executed during training were measured using an optoelectronic measuring device (Elite), both at the beginning and at the end of the training period. Subjects were tested pre- and post-training during isokinetic maximal elbow flexions with constant angular torque (CAT) at 90 degrees (0 degrees = full extension), and at different velocities (60, 120, 180, 240 and 300 degrees x s(-1)) for concentric actions, and -60 and -30 degrees x s(-1) for eccentric and isometric contractions at 90 degrees. In order to verify the levels of activation of the agonist biceps brachii (BB) muscles and antagonist triceps brachii (TB) muscles during maximal voluntary activation, their myoelectrical activities were recorded and quantified as root mean square (RMS) amplitudes, between angles of 75 and 105 degrees . The results show that mean angular velocities between elbow angles of 75 and 105 degrees were similar before [302 (32) degrees x s(-1)] and after [312 (27) degrees x s(-1)] the training period. CAT significantly increased measures at angular velocities of 240 and 300 degrees x s(-1) by 18.7% and 23.5%, respectively. The RMS activity of BB agonist muscles was not significantly modified by training. Post-training normalized RMS amplitudes of TB antagonist muscles were inferior to those observed at pre-training, but values were only significantly different at 300 x s(-1). In conclusion, in this study we attempted to show that an increase of CAT to 240 and 300 degrees x s(-1), though velocity-specific training, may be due, in part, to a lowering of the level of coactivation.

Adult↗
PubMed1997

Effects of the type of recovery training on the concentric strength of the knee extensors.

The aim of this study was to examine the effects of specific concentric and eccentric training on concentric muscular strength following an initial standardized period of excessive training that combined concentric and eccentric actions. For a period of 12 weeks, 37 young elite female basketball players performed standardized training, which included concentric and eccentric actions at 70% and 110% of one-repetition maximum (1-RM), respectively. They were then divided into three groups that followed 12 week programmes which included concentric (C-E/C, n = 13), eccentric (C-E/E, n = 13) or a combination of both concentric and eccentric (C-E/-E, n = 11) exercises. The standardized and specific training programmes consisted of 16 and 8 sets of eight repetitions respectively, performed four times a week. Eleven players who did not participate in either the standardized or specific training programmes served as controls (n = 11). Following the initial 12 weeks of standardized training, the concentric strength of the knee extensors was evaluated isokinetically and using leg-press and squat-jump tests. Significant (P < 0.05) reductions in isokinetic torque, and leg-press and squat-jump performance, were seen. The C-E/C group showed significant (P < 0.05) increases in isokinetic torque, and leg-press and squat-jump performance, after 24 weeks of training when compared with pre-training values. Conversely, no significant differences were noted for the C-E/E and C-E/C-E groups. These findings confirm the mode specificity principle, as only the concentric specific training programme improved the concentric strength of the knee extensors.

Adolescent↗
PubMed1997

Concentric and/or eccentric training-induced alterations in shoulder flexor and extensor strength.

To examine the effect of specific concentric and eccentric training on muscular strength following an initial standardized period of excessive training, shoulder extensors and flexors were tested. The shoulder is a joint particularly susceptible to injury and requires a specific strength training program. For a period of 12 weeks, subjects performed training, including concentric and eccentric actions. Thereafter, they were divided into three groups that performed specific 12-week programs, including either concentric (C-E/C), eccentric (C-E/E), or a combination of both concentric and eccentric exercises (C-E/C-E). Following the initial period of training, significant increases (p < 0.05) in performance were observed for all experimental groups. The C-E/C group showed significant increases (p < 0.05) in performance after 24 weeks of training, especially at high concentric angular velocities. However, the C-E/E group showed significant increases (p < 0.05) only in their eccentric moments. No significant differences were noted for the C-E/C-E group. These findings seem to partly confirm the mode-specificity principle, as only the concentric-specific training program improved concentric and eccentric strength. Moreover, the velocity-specificity principle was strongly supported.

Adolescent↗
PubMed1996

Co-activation and tension-regulating phenomena during isokinetic knee extension in sedentary and highly skilled humans.

The aim of this study was to examine isokinetic torque produced by highly skilled (HS) and sedentary (S) human subjects, during knee extension, during maximal voluntary and superimposed electrical activation. To verify the level of activation of agonist (vastus lateralis, VL, and vastus medialis, VM) and antagonist muscles (semi-tendineous, ST), during maximal voluntary activation, their myo-electrical activities were detected and quantified as root mean square (rms) amplitude. Ten HS and ten S subjects performed voluntary and superimposed isometric actions and isokinetic knee extensions at 14 angular velocities (from -120 to 300 degrees*s(-1)). The rms amplitude of each muscle was normalized with respect to its rms amplitude when acting as agonist at 15 degrees*s(-1). Whatever the angular velocity considered, peak torque and constant angular torque at 65 degrees of HS were significantly higher (P <0.05) than those of S. Eccentric superimposed torque of S, but not HS, was significantly higher (P <0.05) than voluntary torque at -120, -90, - 60 and - 30 degrees*s(-1) angular velocities. For a given velocity, the rms amplitude of VL and VM were significantly lower (P <0.05), during eccentric than during concentric actions, in S, but not in HS. However, whatever the angular velocity, ST co-activation in HS was significantly lower (P < 0.05) than in S. We concluded that co-activation phenomenon could partly explain differences in isokinetic performances. Differences between voluntary and superimposed eccentric torques as well as lower agonist rms amplitude during eccentric action in S, support the possibility of the presence of a tension-regulating mechanism in sedentary subjects.

Adult↗
PubMed1996

Diurnal rhythm of the muscular performance of elbow flexors during isometric contractions.

The influence of time of day on elbow flexion torque was studied. Thirteen physical education students, 7 males and 6 females, made maximal and submaximal isometric contractions at 90 degrees of elbow flexors using a dynamometer. The torque developed was measured on each contraction. The myoelectric activity of the biceps muscle was also measured at the same time by surface electromyography (EMG) and quantified from the root mean square (RMS) activity. Torque and surface EMGs were measured at 6:00, 9:00, 12:00, 15:00, 18:00, 21:00, and 24:00 h over the same day. Oral temperature before each test session was measured on each occasion after a 30-min rest period. We observed a diurnal rhythm in elbow flexor torque with an acrophase at 18:00 h and a bathyphase at 6:00 h, in phase with the diurnal rhythm in oral temperature. However, the diurnal rhythm of temperature did not appear to have any influence on the torque. Links between neuromuscular efficiency and RMS/torque ratio were evaluated by measuring muscle activity along with torque. We also assessed variations in the level of maximal activity of the muscle under maximal voluntary contraction. Neuromuscular efficiency fluctuated during the day, with maximal and minimal efficiency at 18:00 h and 9:00 h, respectively, whereas activation level was maximal at 18:00 h and minimal at 9:00 h. The diurnal rhythm of torque was accounted for by variations in both central nervous system command and the contractile state of the muscle.

Adult↗
PubMed1995

Effects of electromyostimulation and strength training on muscle soreness, muscle damage and sympathetic activation.

Electromyostimulation (EMS) is known to develop muscular strength and hypertrophy. The aim of this study was to compare EMS exercise-induced damage with concentric (CONC) exercise-induced damage. Twelve male athletes were randomly assigned to concentric exercise (five sets of 6 voluntary contractions) or to EMS (30 contractions of 6 s duration, 20 s rest between contractions) on day 0 (D0). The load was 80% of the maximal isometric force. Criterion measures of plasma creatine kinase (CK) activity and lactate dehydrogenase (LDH) activity, and subjective ratings of muscle soreness and urinary catecholamines, were assessed 1 day before and for 3 days after exercise. Among the members of the EMS group, there were significant increases in catecholamine urinary excretion, especially adrenaline (on days D+2 and D+3), plasma CK activity (on day D+2) and plasma LDH activity (on days D+1 and D+2). The changes among the members of the CONC group were smaller and no significant difference was noted. Muscular soreness was greatest in the EMS group, with the peak occurring on day D+2. Comparisons of enzyme release, muscular soreness and urinary catecholamines suggest that EMS induces myofibre membrane damage and a significant increase in sympathetic nervous activity.

Adult↗
PubMed1995

Electrical stimulation and swimming performance.

The purpose of the study was to examine the influence of a 3-wk period of electrostimulation training on the strength of the latissimus dorsi m. and the swimming performances of 14 competitive swimmers divided into 7 electrostimulated (EG) and 7 control swimmers (CG). The peak torques registered during the flexion-extension of the arm was determined with the help of an isokinetic dynamometer at different velocities (from -60 degrees.s(-1) to 360 degrees.s(-1)). Performances were measured over a 25-m pull buoy and a 50-m freestyle swim. For EG, a significant increase of the peak torques was measured in isometric, eccentric, and concentric conditions (P < 0.5). The swimming times declined significantly (P < 0.01) by 0.19 +/- 0.14 s, for the 25-m pull-buoy, and by 0.38 +/- 0.24 s, for the 50-m freestyle. For CG, no significant difference was found for any of the tests. For the whole group, the variations of the peak torques, measured in eccentric condition (-60 degrees.s(-1)) were related to the variations of the performances (r = 0.77; P < 0.01). These results showed that an electrostimulation program of the latissimus dorsi increased the strength and swimming performances of a group of competitive swimmers.

Adult↗
PubMed1994

The influence of electrostimulation on mechanical and morphological characteristics of the triceps surae.

The present study assessed the effects of training using electrostimulation of muscle (EMS) on the torque-angular velocity and torque-angle relationships, and the cross-sectional area (CSA) of the triceps surae. Twelve physical education students, divided into two groups (6 controls, 6 experimental), participated in the experiment. The EMS sessions were undertaken using a 'Complex-type' stimulator. Flexible elastomer electrodes were used. The current used discharged pulses lasting for 200 microseconds at a frequency of 70 Hz. The durations of contraction and rest were 5 and 15 s, respectively. The session lasted for 10 min for each muscle. The training regimen was three sessions per week for 4 weeks. Biomechanical tests were performed with the Biodex (Biodex Corporation, Shirley, NY, USA) isokinetic ergometer. Plantar flexions of the ankle over a concentric range of voluntary contractions were performed at different angular velocities (1.05, 2.10, 3.14, 4.20, 5.23 and 6.28 rad s-1) and maximum voluntary isometric contractions were held for 5 s at several ankle flexion angles (-30 degrees, -15 degrees, 0 degree and 15 degrees; 0 degree corresponds to foot flexion of 90 degrees relative to the leg axis). The peak value of the torque was recorded. Morphological tests consisted of measuring the CSA of the triceps surae on the right leg, 15 cm below the tibial protuberance, by a computerized tomography technique. The torque-velocity relationship was seen to shift significantly upwards after EMS training. The increase in the isometric torque observed after EMS training was greater in dorsiflexion than in plantarflexion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

[Effects of different types of training on torque/angular velocity relationship. Experimental study by isokinetic ergometry in high-level basketball players].

The purpose of this study was to examine the alterations of the Torque/Angular Velocity relationship in knee extensor and flexor muscles due to a long-term training programme. Thirty five young elite basketball players were tested before, after 12 weeks of a common weight-lifting programme (including concentric and eccentric actions) and after 24 weeks including only concentric (C-E/C group) or concentric and eccentric actions (C-E/C-E group). After 12 weeks, significant decrease in torque of knee extensor muscles was observed. In contrast, significant increases in torque of knee flexor and shoulder flexor and extensor muscles were noted. After 24 weeks, significant increases were noted in torque of all muscular groups, for the C-E/C group but not for the C-E/C-E group. It is concluded that training including concentric and eccentric actions have not the same effect on agonist and antagonist muscular groups. The alternation of the contraction mode influences straingthly the strength restoration.

Adolescent↗
PubMed1993

Effect of electrical stimulation training on the contractile characteristics of the triceps surae muscle.

This study aimed to assess the effects of training using electrical stimulation (ES) on the contractile characteristics of the triceps surae muscle. A selection of 12 subjects was divided into two groups (6 control, 6 experimental). The ES sessions were carried out using a stimulator. Flexible elastomer electrodes were used. The current used discharged pulses lasting 200 microseconds at 70 Hz. Contraction time was 5 s and rest time 15 s. The session lasted 10 min for each muscle. Training sessions were three times a week for 4 weeks. Biomechanical tests were performed using an isokinetic ergometer. Subjects performed plantar flexions of the ankle over a concentric range of movement at different angular velocities (60, 120, 180, 240, 300, 360 degrees.s-1) and held isometric contractions for 5 s at several ankle flexion angles (-30/-15/0/15 degrees-0 corresponded to foot flexion of 90 degrees relative to the leg axis). The force-velocity relationship was seen to shift evenly upwards under the influence of ES (P < 0.05). The increased force during the "after" test was greater (P < 0.05) for ankle angle positions of 15 degrees and -30 degrees, which demonstrated a link between the training angle and the gain in strength. No change was noted in the cross-sectional area of the muscle. The results showed that ES allowed the contractile qualities of muscle to be developed in isometric and dynamic conditions. Nervous mechanisms can account for most of these adaptations.

Adult↗
PubMed1988

Impairment of cytomegalovirus and host balance in elderly subjects.

The titres of IgG antibody against "late antigens", "immediate early antigens", and "early antigens" induced by cytomegalovirus (CMV) and IgM antibody against "late antigens" induced by CMV were analysed in 67 geriatric subjects by immunocytochemical techniques. The titres obtained were compared with those of an adult control population. Significantly increased titres of IgG antibody against induced antigens and a significant increase in CMV reactivated infections occurred in the elderly compared with control subjects. These findings indicate that the CMV and host balance in the elderly is disturbed, leading to activation of the CMV latent carrier state that follows primary CMV infection.

Aged↗