Debate exists as to whether the vastus medialis oblique (VMO) can be activated to a greater degree than the vastus lateralis to produce preferential strengthening. This systematic review aims to determine whether preferential activation of VMO can be achieved by altering lower limb joint orientation or muscular co-contraction. A search of pertinent specialist journals and of the electronic databases AMED, CINAHL, the Cochrane database, EMBASE, ovid Medline, Physiotherapy Evidence Database (PEDro), Pubmed, and Zetoc from their inception to February 2008 was undertaken. All English-language clinical papers assessing the electromyographic activity of the human VM against the vastus lateralis (VL) muscles, in a neutral lower limb joint orientation, compared to a different hip, knee, ankle, and foot position; or with the addition of a co-contraction were included. Twenty papers reviewing 387 participants were reviewed. These reported principally that altering lower limb joint orientation or the addition of a co-contraction does not preferentially enhance VMO activity over VL. Nonetheless, the evidence-base presented with a number of significant methodological limitations. Accordingly, well-designed studies evaluating large samples of patients with patellofemoral joint disorders are required, to rectify the present limitations in the evidence-base, and to thoroughly investigate this topic.