Comparison of Kinematic Outputs and Reliability of Plug-in Gait versus Conventional Gait Model 2 During Cycling

Motion analysis is used to measure proper bicycle fit, avoid injury, and improve cycling performance. Small changes in position can impact joint kinematics and risk for overuse injury. Concerns regarding the often-used biomechanical model Plug-in-Gait (PIG) resulted in the creation of Conventional Gait Model 2 (CGM2). This study aims to compare kinematic outputs of these two models for cycling biomechanics plus between-day reliability of each model. Thirty-five participants participated in two experimental sessions. PiG and CGM2 marker sets were applied, and data was collected while cycling between 80-90 rpm. Model outputs were compared using session one kinematic data. Reliability tests used session one and session two data. Differences in kinematics were found between models for hip flexion (CGM2 - PiG mean difference = -8.2° ± 5.2°, p < .001), hip frontal plane (mean = 5.4 ± 4.1°, p < .001), hip transverse plane (mean = -5.3° ± 11.6°, p = .011), knee extension (mean = 1.8° ± 4.2°, p = .015), knee frontal plane (mean = -10.8° ± 9.6°, p < .001), dorsiflexion (mean = -1.7° ± 3.6°, p = 0.005), and plantarflexion (mean = 3.3° ± 5.4°, p < 0.001). CGM2 ICCs were good-to-excellent (> 0.75) for all motions except frontal plane knee motion. PiG ICCs were > 0.75 only for ankle dorsiflexion and plantarflexion. If CGM2 is used to assess bicycle fit, reference values should be adjusted based on the difference between models to ensure an appropriate fit is obtained. CGM2 has better between-day reliability, therefore practitioners may consider using CGM2 for serial fit sessions.