Biomechanical effects of a six-week change of direction technique modification intervention : implications for performance and anterior cruciate ligament injury risk

Background Change of direction (COD) technique modification is effective in reducing potentially hazardous knee joint loads that have the potential to load the anterior cruciate ligament (ACL); however, the implications for performance (i.e., completion time, ground contact time [GCT], exit velocity) remain unclear. Therefore, the aim of this study was to evaluate biomechanical effects of COD technique modification on COD performance and surrogates of ACL injury risk (i.e., multiplanar knee joint loads) during 45° (CUT45) and 90° (CUT90) side-step cutting. Design A non-randomized, controlled 6-week intervention study with a repeated measures preto- post design was used. 16 men (1 dropout) from multidirectional sports formed the intervention group (IG) who participated in two 30-minute COD technique modification sessions (with externally directed verbal coaching cues) per week, while 14 men (2 dropouts) from multidirectional sports formed the control group (CG) and continued their normal training. All participants performed six trials of the CUT45 and CUT90 task whereby pre-to-post intervention changes in lower-limb and trunk kinetics and kinematics were evaluated using 3D motion and ground reaction force analysis. Results Significant main effects for time (pre-to-post changes) were observed for CUT45 completion time, exit velocity, peak KAM and CUT90 completion time ( p ≤ 0.045, η 2 = 0.152-0.539), and significant interaction effects of time and group were observed for CUT45 completion time, GCT, exit velocity and CUT90 completion time ( p ≤ 0.010, η 2 = 0.239-0.483), with the IG displaying superior performance post-intervention compared to the CG ( p ≤ 0.109, g = 0.83-1.35). No significant interaction effects of time and group were observed for CUT45 and CUT90 multiplanar knee joint loads, with no statistically significant and meaningful reductions for the IG ( p ≥ 0.162, g = 0.06- 0.30). However, mixed responses were observed, with five to eight participants in the IG demonstrating increases or decreases in multiplanar knee joint loads during cutting tasks which exceeded the smallest worthwhile change. Conversely, the CG displayed significant increases ( p = 0.002, g = 1.21) in CUT45 peak KAMs post-intervention. Conclusions COD technique modification with externally directed verbal coaching cues resulted in significant and meaningful improvements in side-step cutting performance; primarily attributed to increases in COD velocity profiles, increases in propulsive forces over shorter GCTs, and decreased knee flexion. Based on IG group means, COD technique modification resulted in no statistically significant and meaningful changes in multiplanar knee joint loads. However, on an individual basis, considerable variation was observed in response to the intervention (i.e., positive and negative responders), with “higher-risk” athletes responding positively, and athletes initially considered “lowrisk” tending to increase their multiplanar knee joint loads to magnitudes not considered hazardous or “high-risk”.