Does somatosensory loss induce adaptation of the gait initiation process?

Gait initiation (GI) is the transient period between posture and movement. Its central programming takes into account the environmental constraints as well as the constraints induced by the body itself. Patients with peripheral sensory neuropathies display a severe proprioceptive deficit leading to balance and gait impairments and rely on a variety of compensatory mechanisms and are known to be dependent on vision. GI was studied on eight healthy subjects and five patients in order to assess the effect of somatosensory loss on the different phases of GI, combined with a manipulation of the visual inputs. Our main hypothesis is that the proprioceptive deficit would induce an adaptation of the GI process, especially when modifying the lower part of peripheral vision. The results show that the pathology induces some adaptations of the GI process, characterized by a decrease of the motor performance (assessed by the maximal anteroposterior velocity of the center of gravity at the end of the first step), a decrease in the spatial parameters (assessed by the peak amplitude of the backward shift of the center of foot pressure during the anticipation phase and the length of the first step), and a non-modification of the temporal parameters (assessed by the duration of the anticipation phase and of the first step). The suppression of the lower part of peripheral vision has no effect on the GI process. The role of the lower part of peripheral vision seems therefore to be less critical for GI, than for balance and locomotion.