Background The activity of the gluteal muscles is important in preventing external valgus moment of the knee, which is a major factor in anterior cruciate ligament injury. Therefore, for the prevention of external valgus moment of the knee, we devised the resistive lateral leg reach exercise (RLLR), a single-limb squat with resistance which increases the load placed on the gluteal muscles.

Objective This study investigated the biomechanical and electromyographic characteristics of the support leg during RLLR by comparison to those during the lateral leg reach exercise (LLR), which is similar to RLLR but with no resistance applied.

Design Quasi-experimental study.

Setting Controlled research laboratory.

Participants 10 asymptomatic male college students.

Interventions A 3D motion capture system and force plate were used to perform motion analysis. Surface electrodes recorded Electromyography activity at each muscle site (gluteus maximus, gluteus medius, rectus femoris, vastus medialis, biceps femoris, adductor magnus) during the exercises.

Main outcome measurements External knee valgus/varus moment and internal hip abduction/adduction moment of the support leg were calculated using a software suite. EMG root mean squared amplitude was normalised to a percentage of maximum voluntary contraction (%MVC).

Results RLLR was characterised by a significantly larger internal hip abduction moment (43.7±16.0 Nm) and larger gluteus maximus activity (141±109%MVC) than those observed during LLR (26.1±12.7 Nm, 81±52%MVC, respectively).External knee valgus moment almost did not occur through the motion in RLLR, but did occur during LLR (12.6±9.0 Nm).

Conclusion RLLR serves to increase the load on the gluteal muscles and can be effective for the prevention of external knee valgus moment. It appears to be a promising exercise to prevent anterior cruciate ligament (ACL) injury and to use in rehabilitation training after ACL reconstruction.