Is the knee joint more vulnerable to injury in unplanned cutting tasks? An EMG vector field analysis of high-level female athletes

Objectives: Neuromuscular activation and peak external knee abduction moments (pKAM) are risk factors for anterior cruciate ligament injuries during sidestep cutting. This study aimed to: 1) compare thigh muscle activity between preplanned and unplanned sidestep cuts, 2) assess rank correlations of mean thigh muscle pre-activity in both cuts, 3) investigate the relationship between pKAM and thigh muscle activity in 31 experienced female handball players.

Methods: Four-component (vastus medialis, vastus lateralis, semitendinosus, biceps femoris) electromyogram vector fields were compared from 100 ms before ground contact until toe-off using Statistical Parametric Mapping. Spearman's rank correlation coefficient was used to assess rank correlations of mean pre-activity of individual muscles between cuts. Relationships between pKAM and the four-component electromyogram vector fields were assessed using Canonical Correlation Analysis.

Results: Four-component muscle activity differed before ground contact and push-off, mostly due to activity differences in muscle pairs. Individual analyses showed lower vastus medialis activity in unplanned cuts right before ground contact. High pre-activity rank correlations were found for vastus medialis and lateralis, moderate for semitendinosus, and none for biceps femoris between preplanned and unplanned cuts. Canonical correlation analyses indicated no relationship between muscle activity and pKAM.

Conclusion: The knee might be more vulnerable to injury in unplanned tasks due to lower muscular pre-activity. Muscle activity does not vary with pKAM, suggesting passive structures must absorb higher loads with increasing pKAM. Differences in vastus medialis pre-activity and inconsistencies in biceps femoris pre-activity ranking highlight areas for targeted neuromuscular training to better protect the knee against external loads.