Strategies of muscular support of varus and valgus isometric loads at the human knee

In this paper we studied how subjects activate their muscles in response to static varus and valgus loads at the knee. The muscles' contributions to t he external moments were estimated using an EMG driven biomechanical model of the knee. The individual muscle activation and loading patterns were exa mined to identify the strategies that the nervous system uses to support va rus and valgus knee moments. It was found that the (1) co-contraction of th e hamstrings and quadriceps. and (2) activation of the gracilis and tensor fascia lata increased with the increasing magnitude of the varus and valgus moments. These 2 activation patterns provided positive support of valgus a nd varus loads at the knee The sartorius appears to be activated to provide positive support of valgus loads at the knee. whereas during varus moments this muscle increases the varus load on the knee, i.e. provides negative s upport. Generally, the hamstrings and quadriceps co-contraction contributed to most of the muscular support of the varus and valgus moments. In additi on, co-contraction supported 11-14% of the external moment in pure varus an d pure valgus respectively. It appears that there are activation strategies with the specific purpose to support varus and valgus moments, albeit smal l, which suggest dual goals of the neuromotor system during the support of varus and valgus moments. (C) 2001 Elsevier Science Ltd. All rights reserve d.