Sex-Related Differences in Neuromuscular Control: Implications for Injury Mechanisms or Healthy Stabilisation Strategies?

Sex-related differences in neuromuscular activation have been previously identified and are thought to be an underlying contributor to the ACL injury mechanism. During dynamic tasks evaluating the role of muscle action as it relates to joint stability is difficult since individual muscle contributions to force generation are confounded by biomechanical factors of movement. The purpose of this study was to examine sex-related differences in knee muscle action during a weight-bearing isometric exercise and identify the stabilising role of these muscles. Healthy young adults stood with their dominant leg in a boot fixed to a force platform. A force matching protocol required participants to modulate normalised ground reaction forces in various combinations of anterior-posterior, medial-lateral loads while maintaining a constant joint position. Normalised electromyographic data of eight muscles crossing the knee joint were displayed in polar plots. Patterns were quantified with an orientation analysis and mean activation magnitudes were computed. Females demonstrated symmetrical activation patterns with significantly greater activation in the rectus femoris (p=0.037), lateral gastrocnemius (p=0.012), and tensor fascia lata (p=0.005) compared to males. High between-subject reliability (ICC=0.772-0.977) was observed across groups suggesting we have identified fundamental sex-related differences in knee joint stabilisation strategies. (c) 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:310-317, 2014.