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CLINICAL DEVELOPMENTS: A PHYSICAL THERAPY RESOURCE FOR PHYSICIANS
Volume 1, No.3:
EFFECT OF A NEUROMUSCULAR TRAINING PROGRAM ON THE KINETICS AND KINEMATICS OF JUMPING TASKS
Chappell JD, Limpisvasti O. Am J Sports Medicine. 2008; 36(6):1081-1086.
Abstract and Commentary by Carlee Uhrich, PT, Physical Therapy at Dawn
Females are more likely than males to suffer a non-contact ACL injury, and the reason for this remains unclear. One proposed reason is an altered motor control strategy, which is potentially modifiable through a specific training program. Cutting tasks, cross-cutting tasks, and land-and-jump maneuvers are examples of high-risk activities that have been studied extensively in the literature.
Because neuromuscular training prevention programs have been shown to be promising interventions, the authors compared the kinetics and kinematics of female athletes before and after completing a neuromuscular training program. Also investigated were performance improvements on specific tasks after the intervention. Six weeks of a neuromuscular training program was expected to decrease dynamic knee valgus moments, increase knee flexion angles, and increase hip flexion during the stance phase of both drop jump and stop jump tasks.
A total of 30 female collegiate athletes, all of whom had no history of knee injuries, completed the study. Initial data was collected with each subject completing one drop jump and one vertical stop jump task with no coaching on jumping techniques, and the tasks were performed according to protocols already established in the literature. Data was collected by 18 reflective markers which were attached at landmarks appropriate for collection of trajectories and from a force plate that recorded reaction forces of the right foot.
After the jumping tasks were completed, performance was measured by two vertical jumps for maximum height and three timed repetitions of a single leg hopping task. Each subject was instructed in a set of 10 exercises that focused on core strengthening, dynamic joint stability, balance, jump training, and plyometrics. For six weeks, the exercises were practiced daily for 10-15 minutes.
A decreased knee flexion angle is one proposed risk factor for ACL injury. For the drop jump tasks, both the knee flexion angle at foot strike and the maximum knee flexion angle during stance were significantly greater (P=.003) and (P=.006) respectively.
An excessive valgus moment is another proposed risk factor for ACL injury. Maximum knee valgus moment decreased, however the level did not reach significance. In the stop jump task, there was a decrease in maximum dynamic knee valgus after the training (P=.04).
Both the vertical jump and timed single leg hop tests were significantly improved, (P<.001) for both.
A neuromuscular training program can alter motor control strategies. However, further studies are needed to guide specific parameters regarding length and optimal initiation time for the training programs. Younger athletes may benefit more from a neuromuscular training program because motor control strategies are not yet as firmly established.
This study focused on two specific tasks which represent functional demands of sport and which allowed researchers to investigate suspected risk factors for a non-contact ACL injury. Previous studies have commented on the effectiveness of training programs, and the results have been encouraging. However, there are not many studies that specifically study the kinetics and kinematics of subjects pre and post intervention. This study showed that some risk factors were improved after the intervention, but not all. There are multiple risk factors. As more research is done, we will hopefully gain further insight into how and when to most effectively implement a neuromuscular training program.
There were weaknesses in this intervention from a motor control standpoint. The program was only six weeks, and the exercises were self-directed. The tasks measured were dynamic in nature, and so the type of practice in order to change neuromuscular control strategies needs to fit the demand of these tasks. Simple repetition of exercises would not train for the variability that would be encountered in sport.
Random practice with varying levels of feedback and task specific exercises should be considered in addition to the basic blocks of plyometric and core strengthening exercises. The neuromuscular system needs to be challenged over time in order for new control strategies to reach a more automatic level. Early, precise guidance and challenges may increase the efficacy of neuromuscular control training programs.
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