Walking on a split-belt treadmill (each of the two belts running at a different speed) imposes an asymmetrical gait, mimicking limping that has been observed in various pathologic conditions. This walking modality has been proposed as an experimental paradigm to investigate the flexibility of the neural control of gait and as a form of therapeutic exercise for hemi-paretic patients. However, the scarcity of dynamic investigations both for segmental aspects and for the entire body system, represented by the centre of mass, challenges the validity of the available findings on split gait.

Compared with overground gait in hemiplegia, split gait entails an opposite spatial and dynamic asymmetry. The faster leg mimics the paretic limb temporally, but the unimpaired limb from the spatial and dynamic point of view. These differences suggest that a partial shift in perspective may help to clarify the potential of the split gait as a rehabilitation tool.

The aim of the present study is to investigate the dynamic asymmetries of lower limbs in adults with unilateral motor impairments (e.g. hemiplegia post-stroke, Parkinson's disease, multiple sclerosis, unilateral amputation, surgical orthopedic interventions) during adaptation to gait on a split-belt treadmill. The sagittal power provided by the ankle and the total mechanical energy of the centre of mass will be thoroughly studied. The time course of phenomena both during gait when the belts are running at different speed and when the belts are set back to the same speed (i.e. the after-effect) will be investigated.

A greater dynamic symmetry between the lower limbs is expected after split gait. The question whether this symmetry will occur when the pathological limb is on the faster or the lower belt will be disclosed. Some alterations of the motion of the centre of mass during split gait are also expected.

Inclusion Criteria:

• age between 18 and 70 years old;
• ability to walk for at least 20 meters without support;
• ability to wittingly sign the informed consent form;
• ability to understand the instructions and to complete the motor task;
• visual acuity > 10/20 on the worse side, with optical correction;
• unilateral motor impairments of one lower limb as a consequence of various pathologic conditions, such as (not exhausting list): post-stroke hemiparesis, Parkinson's disease with lateral asymmetry in the motor symptoms, multiple sclerosis with lateral asymmetry in the motor symptoms, unilateral amputation with prosthetic correction, surgical orthopedic interventions, unilateral lesions of peripheral nerves.

Exclusion Criteria:

• systemic neurologic pathologies;
• orthopedic surgical interventions, other than those determining the inclusion criteria;
• symptomatic pathologies of rachis;
• other sensory or neurological pathologies with impact on balance and gait;
• pregnancy.