Epidemiologic study of young soccer player's injuries in U12 to U20.

AIM: The aim of this study was an epidemiological report of the injuries to young soccer players from pretraining centres (12 to 15 years: U12-U15) and training centres (16 to 20 years: U16-U20). METHOD: Over 3 years, 618 injuries were analysed, concerning an average of 137 players per season (66 and 71 players in U12-U15 and U16-U20, respectively). The injuries were diagnosed by a physician. Numerous injury-related information were documented: player, player's age category, date of the injury, site of the injury, injured side, type of injury, circumstances: training vs. match and contact vs non-contact, number of days of play missed, severity, and player's position. RESULTS: The injury rate was higher in matches than in training sessions. Non-contact injuries accounted for 77.0% of the injuries for U12-U15 and 65.6% for U16-U20. The injuries were mainly to the thigh and hip in pretraining players (23.3% and 19.0%, respectively), and to the thigh and ankle in training players (32.1% and 20.3%, respectively). Contact injuries occurred more frequently during matches, presumably because of the higher intensity of play. The analysis of match injuries by position indicated that for U12-U15, during the matches, lateral defenders were injured most often: 30.4%. For U16-U20, axial midfielders and axial defenders were most subject to injuries during the matches (26.6% and 23.1%, respectively). CONCLUSION: These results may help to improve the programming of training. Between the first and third seasons of this study, a decrease in injuries during both matches and training sessions: from 174 to 107 (decrease of 38.5%).

Force-velocity profile: imbalance determination and effect on lower limb ballistic performance.

This study sought to lend experimental support to the theoretical influence of force-velocity (F-v) mechanical profile on jumping performance independently from the effect of maximal power output (P max ). 48 high-level athletes (soccer players, sprinters, rugby players) performed maximal squat jumps with additional loads from 0 to 100% of body mass. During each jump, mean force, velocity and power output were obtained using a simple computation method based on flight time, and then used to determine individual linear F-v relationships and P max values. Actual and optimal F-v profiles were computed for each subject to quantify mechanical F-v imbalance. A multiple regression analysis showed, with a high-adjustment quality (r²=0.931, P<0.001, SEE=0.015 m), significant contributions of P max , F-v imbalance and lower limb extension range (h PO ) to explain interindividual differences in jumping performance (P<0.001) with positive regression coefficients for P max and h PO and a negative one for F-v imbalance. This experimentally supports that ballistic performance depends, in addition to P max , on the F-v profile of lower limbs. This adds support to the actual existence of an individual optimal F-v profile that maximizes jumping performance, a F-v imbalance being associated to a lower performance. These results have potential strong applications in the field of strength and conditioning.

Comparison of the decrease in strength between hamstrings and quadriceps during isokinetic fatigue testing in semiprofessional soccer players.

An imbalance in the agonist/antagonist ratio has been identified as a pathologic factor. Using an isokinetic dynamometer, several studies have investigated the loss of quadriceps strength due to fatigue, but few have explored this phenomenon in the hamstrings. This study assessed the decline in strength of the hamstring and quadriceps muscles with fatigue. The goal was to determine whether a divergence in the decline in strength occurs that would affect the hamstring to quadriceps ratio of endurance. Twenty-seven professional soccer players were selected for endurance testing to evaluate fatigue on an isokinetic dynamometer. The decline in hamstring strength was significantly greater than that of the quadriceps after 15 repetitions for the dominant leg and after 40 repetitions for the nondominant leg. This study also revealed a decline in the endurance ratio compared with the maximal strength ratio in the dominant leg after 30 repetitions. In fatigue states, the decline in hamstring strength diverges from that of the quadriceps in both legs. This difference in resistance to fatigue provokes an imbalance that may affect the stabilizing function of the thigh muscles. These results can be considered as indicators of an increased risk of injury during exhausting effort.