Introduction:​ The forward lunge (FL) is a common weight bearing exercise that simultaneously trains the muscles crossing the hip, knee and ankle joint for strength and endurance. It is commonly used for rehabilitation, injury prevention and improving athletic performance. While the FL is an effective functional exercise, it trains movement primarily in the sagittal plane and previous research has shown that the hip extensors have relatively low activation compared to the knee extensors. Previous research has also shown that by altering the lunge and other lower extremity exercises (i.e., squat and deadlift) it is possible to increase the activation of the hip extensors and muscles that are involved in movements that occur in the frontal plane as well (i.e., abduction/adduction). The purpose of this study is to observe the changes in the kinetics and electromyographic (EMG) activity of the trunk and lower extremities due to variations of the forward lunge exercise.

Methods:​ Eleven recreational athletes were recruited to perform 4 different types of lunges. The 4 lunges completed were the FL, the FL while increasing flexion at the hip causing the trunk to be in a forward position (FLTF), a lunge in which the subject stepped at a 30º angle to widen the step (WSL), and a WSL while increasing flexing at the hip (WSLTF). Each lunge was performed 3 times with two different external loads (13.6 and 27.2 kg) for a total of 24 lunges. EMG electrodes were placed bilaterally on the lower back and abdominal muscles and also on muscles of the hip and thigh of the lead leg during the lunges. A total of thirty three retroreflective markers were placed on the subject and the dumbbells used for the external load. All lunges were done on two portable force platforms while an 8 camera motion capture system recorded the movement. A multivariate ANOVA was used to test for significant differences and interactions between variables.

Results:​ Peak internal hip adduction moment, peak external knee varus moment and peak external knee valgus moment were significantly greater during the wide step conditions compared to the straight forward step conditions (P <​ 0.001). Peak internal hip abduction moment was significantly greater in the straight forward lunges than during the wide step lunges (P <​ 0.001). Peak internal hip extension and L5/S1 extension moments were significantly greater during the lunges with the trunk forward compared to lunges when the trunk was upright (P <​ 0.001) and also with the high external load compared to the low external load (P <​ 0.001). There were no significant differences between any independent variables for the EMG data. There were no significant interactions between any of the independent variables.

Discussion:​ The increased hip adduction moment seen when the width of the step is increased may help to strengthen these muscles and prevent athletic injuries to this muscle group. However, the increased varus and valgus knee moments may make the wide step lunge a poor choice due to increased medial and lateral compression of the knee joint. The increased hip extensor moment seen during the lunges with the trunk in a forward position and higher external loads may help to strengthen these muscles and possibly reduce injury risk to the knee and lower back during athletic movements. However, the increased L5/S1 extensor moment seen with increasing external load and a forward position of the trunk may increase lower back injury risk during lunge exercises.