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Background Charcot-Marie-Tooth (CMT) is a slowly progressive disease characterized by muscular weakness and wasting with a length-dependent pattern. Mildly affected CMT subjects showed slight alteration of walking compared to healthy subjects (HS). Research question To investigate the biomechanics of step negotiation, a task that requires greater muscle strength and balance control compared to level walking, in CMT subjects without primary locomotor deficits (foot drop and push off deficit) during walking. Methods We collected data (kinematic, kinetic, and surface electromyographic) during walking on level ground and step negotiation, from 98 CMT subjects with mild-to-moderate impairment. Twenty-one CMT subjects (CMT-NLW, normal-like-walkers) were selected for analysis, as they showed values of normalized ROM during swing and produced work at push-off at ankle joint comparable to those of 31 HS. Step negotiation tasks consisted in climbing and descending a two-step stair. Only the first step provided the ground reaction force data. To assess muscle activity, each EMG profile was integrated over 100% of task duration and the activation percentage was computed in four phases that constitute the step negotiation tasks. Results In both tasks, CMT-NLW showed distal muscle hypoactivation. In addition, during step-ascending CMT-NLW subjects had relevant lower activities of vastus medialis and rectus femoris than HS in weight-acceptance, and, on the opposite, a greater activation as compared to HS in forward-continuance. During step-descending, CMT-NLW showed a reduced activity of tibialis anterior during controlled-lowering phase. Significance Step negotiation revealed adaptive motor strategies related to muscle weakness due to disease in CMT subjects without any clinically apparent locomotor deficit during level walking. In addition, this study provided results useful for tailored rehabilitation of CMT patients.

s / Gait & Posture 37 (2013) S1–S31 S11Fig. 1. Materialsandmethods:FunctionalMagneticResonanceImag-ing (fMRI) task, consisting in observation of spatial targettrajectories and their recall from memory, was administered to 22healthysubjects.Theobservedmovementsconsistedinupperlimbreaching tasks (Fig. 1A) and computer generated dot movements(Fig. 1B) visualized in subsequent random sequences. The subjecthad to decide if trajectories were congruent with the given target.Control on responses was tested introducing trials with congruentand incongruent targets.Results: The observation of upper limb reaching and dot move-ments induced similar patterns of activations according to acaudo-rostral pathway (including specific areas of the occipital,temporal,parietal,andfrontallobes),seeorangeoverlappingareasin Fig. 2. Similarly, evidence of visual processing of movementswerefoundforthesubsequentretrievaloftheobservedmovement.Furthermore, activations of frontal cortical areas were evidentwhenthesubjectwasdecidingwhetherthetargettrajectorieswerecongruent or not.Discussion: We identified the neural pathways associatedwith visual processing of movement stimuli used in upper limbrobot-mediated training. In both study conditions, activationswere elicited in cerebral areas involved in visual perception, sen-sory integration, recognition of movement, re-mapping on thesomatosensory and motor cortex, memory recall and responsecontrol. Furthermore, we documented the brain’s ability to assim-ilate abstract object movements trajectories with human motorgestures. This results suggest the appropriateness of the visualfeedback provided during robotic motor training. The results ofour study highlight the role of fMRI in improving the understand-ing of visual motor analysis and decision processing during brainreorganisation after training.

Some neurodegenerative diseases at early stage may not drastically affect basic gait ability, whereas more demanding locomotor tasks are more prone to disease-induced abnormalities. In this study, we evaluated the interday test–retest reliability, 4–6 weeks apart, of instrumented movement analysis on a group of 20 subjects with Charcot–Marie–Tooth (CMT) disease considering a set of kinematic and kinetic curves and related parameters obtained during natural walking (NW) and faster walking, heel and toe-walking, step ascending and descending. Results showed that the reliability was good for NW, with the exception of trunk curves, pelvic tilt and EMG profiles (moderate reliability), and trunk ROM in sagittal/transverse plane (poor reliability). Comparing our results with literature, CMT patients did not present a greater variability during NW than healthy subjects or patients with diseases of CNS. Additional locomotor tasks showed a slight reduction of reliability, although the moderate-to-good level shown in NW was almost never reduced to poor. Most of SEM values (absolute measurement errors) were smaller than 5°, a clinically acceptable threshold. In particular THS, an ankle joint related parameter computed across heel and toe-walking tasks, showed an optimal reliability (ICC = 0.95, SEM = 2.7°) and correlation with CMT clinical scores. Toe and heel-walking and step ascending tasks maximised the number of parameters with a moderate-to-good correlation with patients’ clinical status. We concluded that, in addition to natural walking, more challenging locomotor tasks are good candidates to provide reliable and sensitive outcome measures for CMT patients.