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Background: The anticipatory postural adjustments (APA) associated with step initiation are impaired in obese patients (e.g. longer duration, greater lateral center of pressure excursion). This could arise from the known altered internal representation of the body in obese individuals as this representation is crucial for enhancing the processing of foot cutaneous inputs prior to step initiation and for setting the APA.Research Question: The purpose of the study was to examine if the processing of foot cutaneous inputs and the preparation of the APA when planning a step are impaired in obese patients due to their damaged body internal representation (BIR). We also investigated whether these sensorimotor processes will be restored after a 15-day intervention program composed of motor and cognitive activities engaging the BIR without aiming weight loss.Methods: We compared, prior to (D1) and after (D15) the program, the amplitude of the cortical response evoked by foot cutaneous stimulation (SEP) occurring either during quiet standing or during the planning of a step in 18 obese patients (mean body mass index, BMI: 35). The APA were analyzed by measuring the amplitude and latency of the lateral force exerted on the ground.Results and Significance: The SEP amplitude was not significantly different between the standing and stepping tasks at D1, but increased in the stepping task at D15. This enhanced sensory processing was associated with an increased activation of the posterior parietal cortex, suggesting a stronger involvement of the body representation during the planning of the stepping movement after the program. These cortical changes could have contributed to the changes in the temporal dimension of the APA observed at D15. These results suggest that programs targeting different dimensions of the BIR could be beneficial in improving the dynamic balance in obesity. [ABSTRACT FROM AUTHOR]

Important for balance control, the activation of the cutaneous foot receptors largely depends on the speed and amplitude of the body oscillations during standing. Here, we tested the hypothesis that the transmission of cutaneous inputs to the cortex is reduced during prolonged intervals of small body sways due to continued local skin compression and that under such circumstances, central mechanisms trigger large sways to reactivate the cutaneous receptors. We compared the amplitude of the somatosensory cortical potentials (P50-N90) evoked by electric stimulations of the foot sole during either small or large sways in 16 adults that were standing still with the eyes closed. We found greater P50-N90 amplitude when the stimulation occurred during large body sways, consistent with an increased sensory transmission. Importantly, body oscillations computed 200 ms prior to large sways had smaller amplitude than intervals that were not followed by large sways. The hypothesis of a depressed sensory transmission during continued skin compression was supported by our microneurographic recordings showing adaptation/suppression of tactile fibres discharge during continuous pressure applied to the mechanoreceptors. Finally, the hypothesis that large sways during standing correspond to a self-generated functional behaviour to release skin compression is supported by cortical source and EMG analyses showing respectively that large sways were preceded by activation of cortical areas known to be engaged in motor planning (supplementary motor area and dorsolateral prefrontal cortex) and by ankle muscle activations. Together, the present findings provide evidence for an important sensory function of large body sways for balance control. [ABSTRACT FROM AUTHOR]