Strength Training Increases Effect of Feedback-Technique Intervention

Strength Training Increases Effect of Feedback-Technique Intervention

Stephanie Doyle

July 14, 2008 (Orlando, Florida) — New research presented here at the American Orthopaedic Society for Sports Medicine Annual Meeting might ultimately provide clinicians with a foundation from which to design effective and efficient anterior cruciate ligament (ACL) injury-prevention programs.

"Despite the recent successes of some programs in the literature at prospectively reducing ACL risk, there are still a wide variety of areas that warrant investigation," lead researcher Daniel Herman, MD, PhD, from the University of North Carolina at Chapel Hill, told Medscape Orthopaedics. "The focus of my research has been to essentially pick apart these programs, component by component, to determine the mechanism or mechanisms by which they provide benefit. Hopefully, this will help provide clinicians with a foundation of knowledge that they can apply to the population with which they are working."

The ACL is a major stabilizing ligament of the knee. Typically, an ACL tear occurs after a sudden direction change. As much as 80% of ACL injuries are noncontact, and a large majority occur during the landing phase of stop-jump tasks, Herman said. Studies have repeatedly shown that females have a higher rate of noncontact ACL injury than males, and lower-extremity biomechanics is likely the most compelling factor accounting for the sex bias in noncontact ACL injury rates, he said.

The study specifically looked at the effects of augmented feedback instruction, with and without previous strength training, on the lower-extremity kinematics and kinetics of a top-jump task in female recreational athletes. In the study, 29 athletes were randomly assigned to complete 9 weeks of lower-body strength training and 29 received no strength training. A recreational athlete was defined someone who plays a sport, such as basketball, soccer, or volleyball, 1 to 3 times per week, or someone who engaged in such sports at the high-school varsity level and currently competes at least once a month.

The strength-training program used resistance bands and exercise balls. The quadriceps muscles were targeted with a knee-extension exercise, the hamstrings were targeted with a knee-flexion exercise, the gluteus medius was targeted with a hip-abduction exercise, and the gluteus maximus was targeted with a hip-extension exercise.

Athletes underwent video-assisted feedback training, which included reviewing video of stop-jumps and of an expert model. Feedback related to the standardized factors of optimal performance was provided.

Data were collected for both groups after completion of the jump-landing feedback-instruction protocol. Knee- and hip-joint angles and resultant forces and moments were calculated.

Results showed that video-assisted feedback coupled with the supplementary effect of strength training of the knee and hip musculature had a significant effect on the kinetics and kinematics of female recreational athletes.

In addition to significant muscle-strength gains, video-assisted feedback resulted in an increased capacity to improve jump-landing techniques, as demonstrated by reduced anterior shear force, and increases in hip- and knee-flexion angles. Increasing lower-extremity strength alone is not sufficient to alter lower-extremity biomechanics in female recreational athletes, but it might have a supplementary effect on other techniques, such as video-assisted instructional feedback, used to develop jump-landing strategies to decrease the risk for ACL injuries, the study showed.

"Since ACL injuries in females are relatively more common than in males, any research that may ultimately enable us to reduce these injuries is welcome," said Jeffrey H. Berg, MD, from Town Center Orthopaedic Associates, in Reston, Virginia, who was not involved in the study. "Past studies have revealed contradictory findings in regard to preactivity strength and jump training. This study shows us that the reason for this may be that the protective effect of a number of factors likely [correlate] in a more complex manner than previously [thought], and that any effective training needs to be comprehensive [and include] several different training modalities."

The study design and results do not indicate whether or not strength training and video-assisted feedback are necessary components of effective and efficient ACL injury-prevention programs; however, the results, in combination with the published literature, indicate that strength training and jump-landing instruction are necessary for achieving maximal efficacy with other techniques, such as balance and/or plyometric training.

Future research should focus on the effects of different types of strength training and feedback programs that can be accomplished in an efficient manner, Herman said. In addition, the effects of strength training and video-assisted feedback on different populations for varying lengths of time must be understood before evidence-based ACL injury-prevention programs can be designed for at-risk individuals.

Berg said that "the sports-medicine community awaits future prospective research to assess whether this combined training program can lead to a reduction in ACL injuries."

Herman said that more research is needed to determine how best to time these interventions, both within an athlete's career and within a given season.

"We also know very little about how long the protective effects may last. If an athlete participates in an injury-prevention program, does that last a season or does it endure multiple seasons," he asked. "We may need 'in-service' sessions to revisit and update the athlete's motion patterns."

Herman's advice for clinicians is to just "do it."

"The field is still evolving, but there is no evidence that these programs actually harm athletes, so at worst you are engaging in some patient education that this problem can in fact be prevented, and at best you are saving some from a major injury," he said. "You need to consider the characteristics of your population from a variety of perspectives — not only with regard to their strength, conditioning, and motion patterns, but also how much they are willing to do within, before, and between seasons. It has to be efficient as well as effective, or your athletes may not do it."

Funding was provided by the Vladimir Janda Award for Therapeutic Modalities from the Thera Band Academy (Hygenic, Inc.), and student grants from the National Athletic Trainers Association, District III; the University of North Carolina's Injury Prevention Research Center; and the University of North Carolina's Graduate School. The authors disclosed no relevant financial relationships.

American Orthopaedic Society for Sports Medicine (AOSSM) 2008 Annual Meeting. Presented July 12, 2008.