ABSTRACT

The parallel squat and the leg extension are both popular resistance exercises which are reported to enhance the overall strength of the quadriceps muscle group (Earle and Baechle, 2000). According to Signorile et al. (1994) if the parallel squat is exclusively used for quadriceps development it can cause a significant imbalance between the vastus lateralis and vastus medialis muscles. This may be an important issue as muscle imbalance between the vastus lateralis and vastus medialis is a contributing factor in patellofemoral pain syndrome and osteoarthritis of the knee (McConnell, 1986; Galtier et al. 1995; Edwards et al., 2008). As a result it has been recommended by trainers and coaches that the leg extension is a necessary addition to a weight-training programme in order to reduce this imbalance. Empirical studies supporting the assertion that there is a difference in muscle activity between the parallel squat and leg extension are sparse. Furthermore, there appears to be no scientific evidence that leg extension exercise can correct this imbalance. It appears that the notion that supplemental leg extension exercises are needed alongside the parallel squat is based on an unjustified coupling of data produced by previous unrelated studies and long-standing beliefs about the relative activity levels of the various quadriceps muscles (Signorile et al., 1994).