Patients with either incomplete spinal cord injury (iSCI) or stroke suffer from muscle weakness in the lower limb and impaired ambulation. The assessment of motor function in iSCI has so far focused on measures of muscle strength, while in stroke extensive research has been directed towards upper limb motor control. Slowness of movements was reported to be a common motor impairment of patients with lesions of the central nervous system (CNS). It may result from muscle weakness and deficits in dexterity, which is two aspects of motor control that are dependent on cortico-spinal tract (CST) integrity and are crucial to ambulation. Thus, this study investigated the impact of CST damage either at spinal (iSCI) or cortical level (stroke) on ankle dexterity and maximal movement velocity (MMV). Twelve iSCI, stroke and control subjects were tested. The patients were matched for gender, age and maximal voluntary contraction (MVC) in ankle dorsi- and plantar-flexion muscles. Dexterity and MMV were tested in the supine position. CST function was assessed by motor evoked potentials (MEPs). In both groups of patients, MMV and MEP latencies were comparably deteriorated. However, dexterity was preserved in iSCI, but impaired in the hemiparetic stroke leg. Therefore, iSCI patients showed a high dexterity within the preserved muscle strength, but suffered primarily from reduced MMV. In stroke patients, both dexterity and MMV were reduced. These differences might be considered in rehabilitation programs and regeneration therapies.