Altered hip loading and biomechanics in individuals with femoracetabular impingement syndrome (FAIS) may affect the joint's habitual mechanical environment, potentially increasing the risk of osteoarthritis . Examining differences in contributions of muscle and external loads (i.e., gravitational and intersegmental-inertial forces) to hip contact forces, compared with controls, may aid our understanding of FAIS pathomechanics and assist with the development of more effective treatments. Whole-body motion and electromyograms of 14 lower limb muscles were acquired from 41 participants with FAIS and 24 healthy controls whilst walking overground at self-selected speed. Contributions made by muscle and external (gravitational and intersegmental-inertial) forces to hip contact force during the stance phase of walking were estimated using an electromyogram-assisted neuromusculoskeletal model and compared between-groups using statistical parametric mapping. Throughout stance, muscle contributed ∼80% of hip contact force for both participants with FAIS and controls. Compared with controls, participants with FAIS generated ∼20% lower total muscle force (mean difference: -0.75 N·BW