Deceleration affects anticipatory and reactive components of triggered postural responses

• Published in: Experimental brain research 2005-12, Vol.167 (3), p.433-445
• Main Authors: CARPENTER, Mark G, THORSTENSSON, Alf, CRESSWELL, Andrew G
• Format: Article
• Language: English
• Subjects: Acceleration; Adult; Biological and medical sciences; Biomechanical Phenomena; Biomechanics; Ear and associated structures. Auditory pathways and centers. Hearing. Vocal organ. Phonation. Sound production. Echolocation; Electromyography; Fundamental and applied biological sciences. Psychology; Humans; Kinetics; Male; Medicin och hälsovetenskap; Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration; Muscle, Skeletal - physiology; Physical Stimulation; Postural Balance - physiology; Posture; Reaction Time - physiology; Shoulder - physiology; Thorax - physiology; Vertebrates: nervous system and sense organs
• ISSN: 0014-4819; 1432-1106; 1432-1106
• DOI: 10.1007/s00221-005-0049-3

Understanding the physiological and psychological factors that contribute to healthy and pathological balance control in man has been made difficult by the confounding effects of the perturbations used to test balance reactions. The present study examined how postural responses were influenced by the acceleration-deceleration interval of an unexpected horizontal translation. Twelve adult males maintained balance during unexpected forward and backward surface translations with two different acceleration-deceleration intervals and presentation orders (serial or random). "SHORT" perturbations consisted of an initial acceleration (peak acceleration 1.3 m s(-2); duration 300 ms) followed 100 ms later by a deceleration. "LONG" perturbations had the same acceleration as SHORT perturbations, followed by a 2-s interval of constant velocity before deceleration. Surface and intra-muscular electromyography (EMG) from the leg, trunk, and shoulder muscles were recorded along with motion and force plate data. LONG perturbations induced larger trunk displacements compared to SHORT perturbations when presented randomly and larger EMG responses in proximal and distal muscles during later (500-800 ms) response intervals. During SHORT perturbations, activity in some antagonist muscles was found to be associated with deceleration and not the initial acceleration of the support surface. When predictable, SHORT perturbations facilitated the use of anticipatory mechanisms to attenuate early (100-400 ms) EMG response amplitudes, ankle torque change and trunk displacement. In contrast, LONG perturbations, without an early deceleration effect, did not facilitate anticipatory changes when presented in a predictable order. Therefore, perturbations with a short acceleration-deceleration interval can influence triggered postural responses through reactive effects and, when predictable with repeated exposure, through anticipatory mechanisms.