Master of Science (Exercise and Sport Studies)

Anterior cruciate ligament (ACL) injuries occur commonly in non-contact sports, particularly in female athletes, and there are many contributory risk factors. The increased participation of females in sports in recent years has exacerbated the problem. Of the risk factors, the way in which athletes perform sports maneuvers, particularly landing and cutting maneuvers like cross-cut and side-step, holds greatest potential for modification. High varus/valgus and internal/external rotation moments at the knee encountered during sports maneuvers have been established as a risk factor to ACL injury. Plyometric and balance training have been suggested as effective measures to help reduce ACL injury risk; although it is not known which program is superior. The purpose of this study was to evaluate the relative effectiveness of an eight-week plyometric and balance training program on young female netball athletes in terms of reducing varus/valgus, and internal/external rotation moments at the knee, which may have implications on ACL injuries. In addition, the peak vertical joint reaction forces were evaluated to see if they were within safe levels as recommended by earlier research, as excessive joint reaction forces can contribute to ACL rupture.

30 secondary school female netball athletes were assigned to either a plyometric, balance, or control training group. Peak knee joint reaction forces and moments at the knee joint were measured before and after the program for three maneuvers – cross-cut, landing, and side-step. Group differences in peak knee joint reaction force, varus/valgus and internal/external rotation moments were evaluated. Results were analyzed with repeated measures ANOVA individually with speed of approach, playing experience and training group as between- subjects factors. Chi-square analysis was performed on the independence of peak vertical knee joint reaction force, varus/valgus moments, and internal/external rotation moments with speed of approach separately, using playing experience as a layer variable.

No significant group differences were found in magnitude of peak vertical knee joint reaction force and varus/valgus moments for all three maneuvers. The plyometric group showed an increase of 32% in varus/valgus moments post-test for cross-cut, and reductions of 16% for landing, 15% for side-step. The balance group demonstrated an increase of 23% for landing and a decrease of 9% for side-step. Varus/valgus moments were significantly related to speed of approach for the cross-cut maneuver in both novices and experienced athletes (novices: χ = 6.199, p = .013; experienced athletes: = 6.24, p = .012).

The control group landed with greater internal/external rotation moments than the balance group (p = .028). Comparing pre- and post-test results, the plyometric group showed a decrease of 17% in magnitude of internal/external rotation moments for the sidestep. The balance group demonstrated an increase of 16% for cross- cut. Internal/external rotation moments were significantly related to speed of approach during pre-test landing (= 6.533, p = .011).

Although the plyometric and balance training did not contribute much to reduction of peak knee joint reaction forces, there were small reductions on varus/valgus moments in both trained groups for side-stepping maneuvers. Plyometric training also shows potential for reducing internal/external rotation moments for the side-step. balance group (p = .028). Comparing pre- and post-test results, the plyometric group showed a decrease of 17% in magnitude of internal/external rotation moments for the sidestep.

he purpose of this study is to provide a biomechanical analysis of the techniques used by Singaporean female shot putters at both national and college levels. The performance of four women shot putters was examined. Video data were captured using two Panasonic 50 Hz cameras and throws of each shot putter were digitized and analyzed using a Peak Motus three dimensional motion analysis system. Seven variables were examined in this study. The variables were release parameters (angle, height, velocity and horizontal release distance), knee angles and temporal parameters (transition phase and completion phase).

The national athletes threw (17.10m ± 0.40m) about twice as far as the college shot putters (9.17m ± 0.56m). Despite the superior performance of the national athletes over 'the college athletes, the release angle and height of the national athletes were similar to that of the college athletes. This implies that release angle and height might not be accurate indicators for performance. The national athletes, however, displayed higher release velocities than the college athletes and these velocities were in agreement with published studies on elite athletes. The college athletes' low release velocity could have been attributed by their high release angle and release height. This can be explained with the theory of interaction of release parameters of a projectile motion. The college athletes released the shot at a higher percentage of body height as compared to the national athletes. Release distances of the national athletes were only half of the college athletes. A possible biomechanical explanation for this discrepancy was the national athletes needed the distance to counteract the body's forward momentum and to balance the body. They released the shot at a faster velocity compared to the college athletes. Another explanation was because the national athletes' data were collected during competitions, in an effort to avoid fouling, it is possible that the national athletes released the shot too early and therefore sacrifice their released distances. The college athletes' data were collected during training where the direct pressure on foul throw was absent and so they may have performed better with the release distance.

The college athletes also displayed larger knee angles at rear foot touchdown, and a longer duration in the completion phase than the national athletes. Large knee angles at rear foot touchdown do not enhance performance as it limits the use of the legs for force generation. One of the key features of a good shot putting technique is that of a short or possibly no transition phase. Comparing this variable between the two groups of shot putters, the college athletes displayed a shorter transition phase. In fact, the transition phase of the college putters compared well with reported values of published studies. This showed an area of weakness among the national athletes in the area of an inefficient glide. Instead of gliding close to the surface, the national athletes probably went up and down while moving across the throwing circle. A comparatively longer completion phase was found in one of the college athletes. This might imply that the athlete was 'slow' in delivering the shot. This slowness could possibly be an indication of lesser leg strength and power.