title: Time evolution of the organization of multi-muscle postural responses to sudden changes in the external force applied at the trunk level.
abstract: We studied muscle activation patterns in response to perturbations of posture (sudden changes in the external force applied to the thorax) during two time intervals corresponding to pre-programmed postural reactions and voluntary corrections of posture. A hypothesis was tested that a set of postural muscles could be used to form stable groups (M-modes) whose composition changes in different time intervals after a perturbation. Perturbations were applied at the sternum level to standing subjects at an unexpected time. Principal component analysis with factor extraction allowed to identify sets of three factors (M-modes) during the two time intervals, 80-180 ms (T(1)) and 250-450 ms (T(2)) after the perturbation. The composition of M-modes was similar within each time interval across subjects and perturbations but differed significantly between T(1) and T(2). In particular, M-modes during T(1) were characterized by more co-contraction patterns. The results suggest that the neural controller is able to rearrange M-mode composition in real time based on a safety-efficacy trade-off. The results also support the idea that M-modes represent synergies in the muscle space, while they may be used as elemental variables to form synergies at a higher hierarchical level to produce desired mechanical effects.
authors.affiliation: Department of Kinesiology, The Pennsylvania State University, Rec. Hall-268N, University Park, PA 16802, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Robert
authors.forename: Mark L
authors.initials: ML
authors.lastname: Latash
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D008297:Male; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D025341:Principal Component Analysis; D011930:Reaction Time / Q000502:physiology; D013997:Time Factors; D016474:Weight-Bearing / Q000502:physiology