Comparison of Plug-in Gait and CGM2.3 models reveals systematic differences in joint kinematics and kinetics

Abstract This study compared two widely used biomechanical models—Plug-in Gait (PiG) and Conventional Gait Model 2.3 (CGM2.3)—during overground walking (WALK) and single-leg squats (SLS) in 24 healthy adults. Data were collected using a 20-camera Vicon system and force plates. Static trials were analyzed with medial knee and ankle markers to align joint axes across models. Kinematic and kinetic outputs were compared from full movement cycles using root mean square differences (RMSD) and statistical parametric mapping (SPM) paired t-tests. During walking, PiG produced greater internal rotation at the knee (RMSD 17.8°, p < 0.001) and hip (RMSD 5.0°, p < 0.001), and smaller sagittal-plane flexion angles (RMSD 2.6° knee, 2.3° hip) compared with CGM2.3. In single-leg squats, these discrepancies increased to 29.1° and 9.0°, respectively, with sagittal-plane differences of 4.4° at the knee and 5.1° at the hip. CGM2.3 yielded higher knee flexion moments (31% in WALK, 104% in SLS), while PiG produced higher frontal-plane knee moments (28% and 89%). The differences were most pronounced at deeper flexion angles. These results demonstrate that biomechanical outcomes differ systematically between models, emphasizing the impact of model selection on joint kinematics and kinetics in human movement analysis.