Effect of stance width on lower extremities joint kinematics during a squat jump by musculoskeletal modeling in OpenSim software

Squatting is a core exercise for many purposes [1,2]. Exercises related to movements from daily activities are of major interest within physical exercise development and research. Squatting features components of everyday functional movements such as walking, ascending and descending stairs, sitting down, and standing up [3]. The joint kinematics during squatting is crucial for positive adaptation and to avoid injury. The purpose of this study was to assess whether changing the stance width has an effect on the lower limb kinematics and range of motion of hip flexion, knee flexion, and ankle dorsiflexion during an unloaded squat jump. What is the relationship between stance width and lower extremity kinematics? Twenty healthy, young adults (68.3±7.5 kg, 178±5.3 cm, 27.5±4.5 years) performed unloaded jump squats at three different stance widths (40 cm, 60 cm, and 80 cm). Ten Vicon motion captures (Vicon MX, Oxford, UK, 200 Hz) were used to measure the location of the markers [4]. A musculoskeletal model with a total of 10 bodies and 92 muscles was used to estimate joint kinematics in OpenSim. The inverse kinematics tool was used to estimate the angles of the lower limb [1,5–7]. The ANOVA results for comparison of joint angles for the three stance widths, at 10° intervals of thigh orientation during the squat, indicated that joint angles tended to be larger when stance width was narrower, with the most significant effects on ankle dorsiflexion. A greater stance width also tended to be associated with lower hip, knee, ankle angles. Suitable stance width should be chosen according to the targeted joint angles. In order to avoid injury, special care should be taken in extreme positions where large knee and hip joint angles were observed. Sport scientist, coaches, trainers, and sport engineers can use these valuable results.