title: Keeping your balance while balancing a cylinder: interaction between postural and voluntary goals.
abstract: The present study investigated whether postural responses are influenced by the stability constraint of a voluntary, manual task. We also examined how task constraint and first experience (the condition with which the participants started the experiment) influence the kinematic strategies used to simultaneously accomplish a postural response and a voluntary task. Twelve healthy, older adults were perturbed during standing, while holding a tray with a cylinder placed with the flat side down (low constraint, LC) or with the rolling, round side down (high constraint, HC). Central set changed according to the task constraint, as shown by a higher magnitude of both the gastrocnemius and tibialis anterior muscle activation bursts in the HC than in the LC condition. This increase in muscle activation was not reflected, however, in changes in the center of pressure or center of mass displacement. Task constraint influenced the peak shoulder flexion for the voluntary tray task but not the peak hip flexion for the postural task. In contrast, first experience influenced the peak hip flexion but not the peak shoulder flexion. These results suggest an interaction between two separate control mechanisms for automatic postural responses and voluntary stabilization tasks.
authors.affiliation: Faculty of Medical Sciences, Center for Human Movement Sciences, University of Groningen, University Medical Center Groningen, Antonius Deusinglaan 1, 9713 AV, Groningen, The Netherlands. s.papegaaij@umcg.nl
authors.forename: Selma
authors.initials: S
authors.lastname: Papegaaij
authors.forename: Andrea C
authors.initials: AC
authors.lastname: de Lima-Pardini
authors.forename: Beth A
authors.initials: BA
authors.lastname: Smith
authors.forename: Egbert
authors.initials: E
authors.lastname: Otten
authors.forename: Rajal G
authors.initials: RG
authors.lastname: Cohen
authors.forename: Fay B
authors.initials: FB
authors.lastname: Horak
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D003627:Data Interpretation, Statistical; D004576:Electromyography; D005260:Female; D006040:Goals; D006801:Humans; D008297:Male; D008875:Middle Aged; D009038:Motion; D018482:Muscle, Skeletal / Q000502:physiology; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology