ACL injuries occur during sports when the ligament is loaded with forces greater than it can withstand. They can lead to short-term consequences and long-term disability, including early onset osteoarthritis. (3) Injury prevention programs have been shown to be an effective way of reducing ACL injury risk through neuromuscular training. (3) However, despite early success in training programs, overall ACL injury rates have not diminished over time. (4) The level of adoption of and compliance in injury prevention programs remains low, as laboratory-based training methods require considerable time, equipment, and money. (4) To address current shortcomings, there is a need for ACL injury prevention methods that are more accessible and effective for athletes in the long term.

The lack of long-term effectiveness of neuromuscular training programs may be due to a lack of retention and transference of learned movements to the real-life sport. (1) Retention is shown in athletes’ ability to remember and execute learned motor skills after a period of time has elapsed, while transference deals with whether they can execute these skills under different conditions. (6) ACL injury prevention programs usually consist of practicing motor skills in a controlled, predictable environment, which stands in direct contrast to the highly unpredictable, complex environment of competitive sport. (5) Athletes need to be able to transfer motor skills from conscious control to automatic movements in order to minimize real-life injury risk. (4) Attentional focus and implicit learning may address this challenge in retention and transference of movement patterns.

Learning new motor skills can be done using either an internal focus of control, focusing on the movements themselves, or an external focus of control, focusing on the effects of movement. The latter type of attentional focus is found to improve the retention and transference of motor skills by recruiting automatic movement processes. As a result, the recruitment of these skills requires less attentional demands, leaving more attentional capacity available for other game factors. (5) Similarly, in contrast to explicit learning which emphasizes cognitive control over movements, implicit learning may improve anticipatory skills. (5) Research has shown that athletes are at higher risk of ACL injury during competitive game situations, where both psychological and physical pressure and fatigue play an important role in the degree of movement control. (2,4) In these situations, athletes need to be able to recruit low-risk movement techniques as automatically as possible.

How can ACL injury prevention programs apply these principles of motor learning to optimize training for at-risk athletes? Research has shown that biofeedback on exercises improves task performance and influences motor memory. In one study, task-based electromyographic biofeedback during gait retraining of stroke patients was shown to be more effective in maintaining treatment improvements 6 weeks after training compared to usual rehabilitation. (7) Another study using verbal and real-time visual biofeedback during treadmill gait training found significant reductions in knee hyperextension that persisted 1 month after initial training and that also transferred to overground walking. (8) While more research needs to be done to determine if these skills can be retained longer than 1 month, the initial results show improvements in transference. Real-time biofeedback can similarly apply to ACL injury prevention. So far, preventative training efforts have focused on drill behavior. The next logical step would be to give feedback during sports behavior to see if athletes’ retention and transference is improved. Here, wearable real-time feedback also has the advantage over traditional verbal training in being easily incorporated into team practice or training sessions while remaining individualized for the athlete. (1)

Do you see real-time feedback as the next step to improving retention and transference in ACL injury prevention?


1. Benjaminse, A., Gokeler, A., Dowling, A. V., Faigenbaum, A., Ford, K. R., Hewett, T. E., . . . Myer, G. D. (2015). Optimization of the Anterior Cruciate Ligament Injury Prevention Paradigm: Novel Feedback Techniques to Enhance Motor Learning and Reduce Injury Risk. Journal of Orthopaedic & Sports Physical Therapy, 45(3), 170-182. doi:10.2519/jospt.2015.4986

2. Shultz, S. J., Schmitz, R. J., Benjaminse, A., Collins, M., Ford, K., & Kulas, A. S. (2015). ACL Research Retreat VII: An Update on Anterior Cruciate Ligament Injury Risk Factor Identification, Screening, and Prevention. Journal of Athletic Training, 50(10), 1076-1093. doi:10.4085/1062-6050-50.10.06

3. Fox, A. S., Bonacci, J., Mclean, S. G., Spittle, M., & Saunders, N. (2015). A Systematic Evaluation of Field-Based Screening Methods for the Assessment of Anterior Cruciate Ligament (ACL) Injury Risk. Sports Medicine, 46(5), 715-735. doi:10.1007/s40279-015-0443-3

4. Benjaminse, A., & Otten, E. (2010). ACL injury prevention, more effective with a different way of motor learning? Knee Surgery, Sports Traumatology, Arthroscopy, 19(4), 622-627. doi:10.1007/s00167-010-1313-z

5. Gokeler, A., Seil, R., Kerkhoffs, G., & Verhagen, E. (2018). A novel approach to enhance ACL injury prevention programs. Journal of Experimental Orthopaedics, 5(1). doi:10.1186/s40634-018-0137-5

6. Retention of Sport Skills – IResearchNet. (2016, November 01). Retrieved August 20, 2020, from

7. Jonsdottir, J., Cattaneo, D., Recalcati, M., Regola, A., Rabuffetti, M., Ferrarin, M., & Casiraghi, A. (2010). Task-Oriented Biofeedback to Improve Gait in Individuals With Chronic Stroke: Motor Learning Approach. Neurorehabilitation and Neural Repair, 24(5), 478-485. doi:10.1177/1545968309355986

8. Teran-Yengle, P., Birkhofer, R., Weber, M. A., Patton, K., Thatcher, E., & Yack, H. J. (2011). Efficacy of Gait Training With Real-Time Biofeedback in Correcting Knee Hyperextension Patterns in Young Women. Journal of Orthopaedic & Sports Physical Therapy, 41(12), 948-952. doi:10.2519/jospt.2011.3660