Lower-limb biomechanics in motor neuron disease: a joint-level perspective of gait disruption

Background: Motor neuron disease (MND) profoundly impacts mobility, yet gait-specific dysfunctions due to MND remain poorly understood. Methods: We characterized lower-limb gait alterations in people living with MND (plwMND) using advanced biomechanical tools. Nine plwMND and nine non-neurodegenerative disease controls walked on an instrumented treadmill at self-selected speeds. Ground reaction forces and joint motions were measured to model lower-limb kinetics, kinematics, and energetics. Results: PlwMND had reduced forward propulsive (p < 0.001) and braking (p = 0.002) ground reaction forces. Ankle range of motion was 10.0 ± 3.1° lower (p = 0.035) with peak positive ankle moment and power 33% and 72% lower, respectively (both: p < 0.001), in plwMND compared to controls. Conclusions: These lower-limb impairments highlight the ankle as an early and critical locus of dysfunction, with distal weakness driving compensatory proximal strategies, increasing walking inefficiency and fatigue. Integrating biomechanical and clinical data offers new insights into gait disruption in MND, supporting the development of targeted, personalized interventions to maintain independent mobility.