Athletes with a History of ACL Reconstruction Exhibit Greater Inter-Limb Asymmetry in Impact Forces During the First Landing of a Drop Vertical Jump Compared to the Second Landing.

The primary objective of this study was to examine the degree of inter-limb asymmetry in impact force magnitudes and rates during the first and second landings of a drop vertical jump in adolescent athletes with a history of anterior cruciate ligament (ACL) reconstruction. We also compared the degree of asymmetry exhibited by the athletes who had undergone ACL reconstruction to a group of uninjured athletes. This study included 14 athletes who had undergone ACL reconstruction and 28 uninjured athletes, matched for age, sex, and sport. All athletes completed a double-leg drop vertical jump task. Peak vertical ground reaction forces (vGRFs) and loading rates were examined for both limbs during the first and second landings of the drop vertical jump. For the athletes who had undergone ACL reconstruction, peak vGRFs were 11.9% greater for the uninvolved limb vs. the involved limb during the first landing; however, peak vGRFs were only 2.4% greater for the uninvolved limb (vs. the involved limb) during the second landing. The athletes who had undergone ACL reconstruction exhibited greater asymmetry in peak vGRFs for the first landing compared to the uninjured athletes; however, there was no difference between the groups (ACL reconstruction, uninjured) for the second landing.

Instructions Promoting an External Focus Are More Effective for Altering Impact Forces in Female Runners.

CONTEXT: Previous studies have found that instructions promoting an external focus (EF) tend to be more effective for movement pattern retraining compared to instructions promoting an internal focus (IF), for a variety of movement tasks. However, few studies have examined how different types of instructions affect running mechanics associated with running-related injury risk. Therefore, the purpose of this study was to compare the effects of instructions promoting different attentional foci on impact forces during running. DESIGN: Cross-sectional study. METHODS: Twenty uninjured female recreational runners ran at a self-selected speed with their typical pattern (no instructions condition) on an instrumented treadmill that measured ground reaction forces. Next, they were given 2 sets of instructions intended to alter their running pattern; one promoted an IF and the other promoted an EF. Repeated-measures analysis of variance was used to compare impact peaks and loading rates across the conditions (no instructions, IF, and EF), with post hoc tests conducted in the case of a significant omnibus test. RESULTS: There were differences among the conditions in the impact peaks (P < .001) and loading rates (P < .001). Impact peaks were lower for the IF (P = .002) and EF (P < .001) conditions compared to the no instructions condition. Loading rates were lower for the EF condition compared to the no instructions (P < .001) and IF (P < .001) conditions; there was no difference between the IF and no instructions conditions (P = .24). CONCLUSIONS: Our findings indicate that instructions promoting an EF may be more effective at reducing loading rates during running compared to instructions promoting an IF. Clinicians should consider these findings when attempting to retrain a runner's running pattern.