MUSCLE COORDINATION DURING SIDESTEP CUTTING. CAN THE COORDINATION BE INFLUENCED BY PROPHYLACTIC TRAINING?

Abstract

INTRODUCTION The incidence. of anterior cruciate ligament (ACL) injuries is reported to be high during the popular team sports like soccer, basketball, volleyball and team handball.The most highly risked movement in team handball is reported to be the sidestep cutting maneuver (Strand, 1990. Well-rehabilitated ACL-deficient athletes have been shown to have increased co-contraction about the knee joint (Walla, 1985). The aim of this study was to examine the effect of a prophylactic training program on the co-contraction of non-injured team handball players. METHODS 16 male subjects were divided into a test group (9 subj.) and a control group (7 subj.). The test group performed 5 different exercises under supervision, twice a week for 12 weeks. The exercises consisted of 1)one-legged squats, 2)ham-string pulls, 3)hip abductions, 4)one-legged 'coordination jumps' where the test subject should repetitively hit special marks on the floor without losing his balance 5)one-legged jumps to the side, and. The exercises were designed in a progressive manner in order to increase the strain on the athletes during the whole training period. All exercises are widely used at different stages of the rehabilitation of ACL-deficient patients. To measure the co-contraction EMG-electrodes were applied on 6 selected muscles, influencing the knee. The subjects then performed 10 repetitions of a sidestep cutting maneuver similar to their normal 'match-like' cutting maneuver on a forceplatform and the EMG-signals and the forceplatform signals were simultaneously stored on a personal computer. Maximal voluntary contractions and the corresponding EMG activity were measured for each muscle group. RESULTS The test group showed a significantly shorter ground contact phase after the training (p<0.05), but the coordination patterns did not change. The results showed no effect of the training on the co-contraction ratios during the sidestep cutting. The variation of the center of pressure during ground contact can be used as a measure of the balance. There was no changes in the variation of the center of pressure. The test group showed a great increase in the maximal number of repetitions in exercises 1)-3) and 5), but there was an increase in the MVC only in the hamstring muscles. CONCLUSION The results clearly demonstrated, that rehabilitation exercises cannot increase co-contraction about the knee joint in healthy athletes during sidestep cutting. This is contradictory to the effect on ACL-deficient athletes. One possible explanation is, that the stress imposed by the exercises on the other proprioceptive structures in an ACL-deficient knee is much larger than in a non-injured knee, because of the lack of mechanical stability. The neural input would therefore be much stronger, and possibly able to modulate the existing motor programs. REFERENCES STRANDT , TVEDTER , ENGEBRETSENL, TEGNANDER A: ACL-injuries in team handball. Tidsskr. Nor. Iregeforen. 1 10;22225. 1990. (Norwegian). WALLA DJ, ALBRIGHT JP, MCAULEY E, MARTIN RK, ELDRIDGEV, EL-KHOURYG : Hamstring control and the unstable anterior cruciate ligament-deficient knee. Arn.j.sports.med. 13;34-39.1 985.