Effects of fatigue on lumbar biomechanics and muscle activation across different lifting techniques: an OpenSim-based analysis

Background Deadlift movements are widely used in athletic training, but how lifting technique and fatigue affect lumbar kinematics, net generalized segmental joint moments, and surface-EMG responses in Wushu athletes remains unclear. Purpose This study compared forward-bending (FB), half-squat (HS), and deep-squat (DS) lifting to characterize lumbar kinematics, net generalized segmental joint moments, and surface-EMG responses before and after a fatiguing protocol. Methods Fifteen male Wushu athletes performed standardized lifting tasks. Kinematic and kinetic data were analyzed using OpenSim-based scaling, inverse kinematics, and inverse dynamics with a subject-specific scaled Full-Body Lumbar Spine model to calculate lumbar kinematics and net generalized segmental joint moments. EMG processing yielded MVC-normalized muscle-activation profiles, unnormalized integrated EMG Integrated electromyographic, and median-frequency measures. Statistical analyses included repeated-measures ANOVA and paired-samples t-tests. Results Technique- and fatigue-related differences were observed in selected lumbar kinematic, net generalized segmental joint-moment, and surface-EMG outcomes. FB showed greater lumbar flexion and higher semitendinosus IEMG, whereas HS and DS exhibited smaller lumbar excursions. HS and DS did not consistently produce lower net generalized segmental joint moments across lumbar levels. Fatigue was associated with delayed peak-moment timing and lower IEMG in several recorded muscles. Conclusion The HS technique showed an intermediate pattern of lumbar excursion and segmental net intervertebral joint moments. These findings characterize technique-dependent patterns in lumbar kinematics and net generalized segmental joint moments.