BACKGROUND: Implicit (IF) and explicit (EF) feedback are two motor learning strategies demonstrated to alter movement patterns. There is conflicting evidence on which strategy produces better outcomes. The purpose of this study was to examine the effects of reduced IF and EF video feedback on lower extremity landing mechanics. METHODS: Thirty participants (24 +/- 2 years, 1.7 +/- 0.1 m, 70 +/- 11 kg) were randomly assigned to three groups: IF (n = 10), EF (n = 10), and control (CG) (n = 10). They performed twelve box-drop jumps three times a week on the training sessions for six weeks. Only IF and EF groups received video feedback on the training sessions. IF was cued to focus their attention on the overall jump, while EF was cued to focus on position of their knees. 3D lower extremity biomechanics were tested on testing sessions with no feedback. All sessions were at least 24 h apart from another. Testing sessions included baseline testing (pretest), testing after 3 training sessions with 100% feedback (pst1), testing after 6 training sessions with 33.3% feedback (pst2), testing after 6 training sessions with 16.6% feedback (Pst3), and testing 1 month after with no feedback (retention (ret)). ANOVA compared differences between groups and time at initial contact and peak for hip flexion (HF, degree) and abduction angle (HA, degree), hip abduction moment (HAM, Nm/kgm), knee flexion (KF, degree) and abduction angle (KA, degree), knee abduction moment (KAM, Nm/kgm) and VGRF (N) (p < 0.05). RESULTS: A significant main effect for group was found between IF and EF groups for HA (IF -6.7 +/- 4; EF -9.4 +/- 4.1) and KAM (IF 0.05 +/- 0.2; EF -0.07 +/- 0.2) at initial contact, and peaks HA (IF -3.5 +/- 4.5; EF -7.9 +/- 4.7) and HAM (IF 1.1 +/- 0.6; EF 0.9 +/- 0.4). A significant main effect for time at initial contact for HF (pre 32.4 +/- 3.2; pst2 36.9 +/- 3.2; pst3 37.9 +/- 3.7; ret 34.1 +/- 3.7), HAM (pre 0.1 +/- 0.1; pst1 0.04 +/- 0.1; pst3 0.1 +/- 0.01), KA (pre 0.7 +/- 1.1; pst1 0.2 +/- 1.2; pst3 1.7 +/- 1), and KAM (pre 0.003 +/- 0.1; pst3 0.01 +/- 0.1) was found. DISCUSSION/CONCLUSION: We found that implicit feedback produced positive changes in landing mechanics while explicit feedback degraded motor learning. Our results indicate that implicit feedback should be used in programs to lower the ACL injury risk. We suggest that implicit feedback should be frequent in the beginning and not be reduced as much following the acquisition phase.

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