The effect of thigh muscle activity on anterior knee laxity in the uninjured and anterior cruciate ligament-injured knee

Massimo G. Barcellona, Matthew C. Morrissey*, Peter Milligan, Andrew A. Amis

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    21 Citations (Scopus)


    Purpose: The main purpose of this study was to describe the nature of the relationship between hamstring muscle activity and anterior knee laxity.

    Methods: This was a cross-sectional study. Anterior knee laxity was measured at 133N and manual maximal forces using the KT2000 knee arthrometer, in 8 ACL-injured and 13 uninjured individuals. Electromyographic activity of the lateral hamstrings was measured during laxity testing. Subjects contracted the hamstrings during anterior knee laxity testing at eight predetermined levels of maximal voluntary isometric contraction.

    Results: Volitional contraction of the lateral hamstrings reduced anterior knee laxity logarithmically for both the 133N and manual maximal tests in both the ACL-injured and uninjured knees. A simple linear regression model, with the log of percentage of maximum lateral hamstrings activity as the sole predictor, explained approximately 70–80 % of the variation in anterior knee laxity. Both ACL-injured and uninjured subjects reduced anterior knee laxity at the same rate with increases in muscle activity. However, initial lateral hamstrings muscle activity had a greater effect on percentage anterior knee laxity scores in the ACL-injured as compared to the uninjured knee.

    Conclusions: Lateral hamstrings activity reduces anterior knee laxity in a nonlinear manner, whereby the initial lower level of activation produces the greatest change in anterior knee laxity. Therefore, hamstrings muscle activity must be monitored during anterior knee laxity testing.

    Original languageEnglish
    Pages (from-to)2821-2829
    Number of pages9
    JournalKnee Surgery, Sports Traumatology, Arthroscopy
    Issue number11
    Publication statusPublished - 1 Jan 2014


    • Anterior cruciate ligament
    • Arthrometer
    • Electromyography
    • Tibial anterior laxity


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