Kinetical Analysis of Lower Limb Joints During Single-Leg Squats and Implication of Rehabilitation

Abstract

Background: The single-legged squat has become popular as an assessment technique and an effective exercise during treatment programs of several conditions. The aim of this study was to investigate the kinetic parameters of the standing leg of the lower limb joints and muscle activity during the unilateral limb squat with front (90-degree hip and knee flexion) and back (neutral hip and 90-degree knee flexion) positions of the non-stance leg. Methods: Fifteen participants (ten male and five female) with weight 71.14±11.86 kg and height average 168.99±8.88 cm performed walking trials and two types of the single leg squat with two postures. Hip, knee and ankle angles, forces, moments and powers were calculated using Plug-in-Gait model. Using Electromyography, muscle activities including rectus femoris, biceps femoris, vastus lateralis, gastrocnemius and tibialis anterior muscles were captured at the same time of squatting and walking. Results: During the front and back position of the swing leg, the squatting leg achieved the higher values of hip and ankle forces in the anterior-posterior direction, and knee force was in the vertical direction in compared with walking. However, during walking, only ankle force was increased in anterior-posterior direction, while hip and knee force reached the highest values in the vertical plane. Considering the moment level, hip, knee and ankle moments achieved the higher level in the sagittal plane. Regarding power values, maximum value of knee power was during the back squat, while walking had the maximum hip and ankle power. In addition, all of the five muscles (rectus femoris, biceps femoris, vastus lateralis, tibialis anterior and gastrocnemius) achieved the higher level of activation during the front squat comparing with walking and back squat except vastus lateralis which reached the peak during the back squat. In details, rectus femoris was activated more than triple times during squats compared with walking, vastus lateralis ix achieved double activation level of walking and biceps femoris get more than 70% higher than walking activation level. Conclusion: Considering the hip joint, the front squat boosted the range of motion by 27% in the frontal plane, while the back squat raised the sagittal hip angle by 41% and anterior-posterior force by 50% and greater than double transverse moment level compared with walking. The knee joint was the most influenced joint during the squat techniques compared with walking particularly knee moment and power. In the sagittal plane, knee moment increased by more than 50% during both front and back squats compared with walking, while knee power achieved higher than 45% and 61% during anterior and posterior squats respectively in comparison with walking. In addition, the ankle force in the medial-lateral direction was raised by 39% via front squat and 50% via back squats higher than walking. Besides, squat techniques achieved a higher level of stimulation of rectus femoris, biceps femoris, vastus lateralis, tibialis anterior and gastrocnemius muscle compared with walking. The most stimulated muscles are rectus femoris and vastus lateralis that were activated by greater than double of walking-related muscle activation. Therefore, the unilateral limb squat could be utilized as a part of the rehabilitation program for different clinical cases to achieve several treatment goals simultaneously. Keywords: Single leg squat, unilateral leg squat, kinematics, kinetics, muscle activity, rehabilitation, strengthening, assessment