Muscle synergies involved in preparation to a step made under the self-paced and reaction time instructions

OBJECTIVE To investigate multi-muscle synergies during preparation to making a step and their changes with speed of stepping and method of step initiation, self-paced vs. reaction-time. METHODS Standing healthy persons performed stepping tasks under 3 instructions, 'comfortably, self-paced', 'very quick, self-paced', and 'as fast as possible to a visual signal'. Electromyographic (EMG) signals of 10 postural muscles were recorded and analyzed. The participants also performed standard tasks associated with releasing a load. These trials were used to identify muscle groupings (M-modes) associated with shifts of the center of pressure (COP) and relations between small changes in the M-modes and COP shifts. The framework of the uncontrolled manifold hypothesis was used to partition the EMG variance across stepping trials into two components that kept constant and changed the COP coordinates in the anterior-posterior (AP) and medio-lateral (ML) directions. RESULTS Muscle synergies stabilizing COP trajectories in both AP and ML directions were observed in both the stepping and supporting legs. The synergies tended to weaken and disappear close to the moment of take-off. They showed only minor differences across the 3 tasks. In contrast, mechanical and EMG characteristics of postural adjustments to stepping were significantly larger and showed higher rates of change during quick steps and steps under the reaction-time instruction. CONCLUSIONS COP shifts associated with preparation to making a step are stabilized by multi-muscle synergies. These synergies are robust across stepping speed and methods of step initiation, self-paced and reaction-time. SIGNIFICANCE Studies of multi-muscle postural synergies are important for understanding postural disorders in neurological patients and changes in postural strategies with age.

[1]  J. Massion.  Movement, posture and equilibrium: Interaction and coordination , 1992, Progress in Neurobiology.

[2]  M. Latash,et al.  Muscle modes during shifts of the center of pressure by standing persons: effect of instability and additional support , 2004, Experimental Brain Research.

[3]  R. Elble,et al.  The initiation of normal walking , 2004, Movement disorders : official journal of the Movement Disorder Society.

[4]  H. Diener,et al.  Disturbances of motor preparation in basal ganglia and cerebellar disorders. , 1989, Progress in brain research.

[5]  C. Assaiante,et al.  Development of Postural Adjustment During Gait Initiation: Kinematic and EMG Analysis , 2000, Journal of motor behavior.

[6]  Wynne A. Lee,et al.  Effects of arm acceleration and behavioral conditions on the organization of postural adjustments during arm flexion , 2004, Experimental Brain Research.

[7]  Jennifer Henke,et al.  Influence of Elderly Executive Cognitive Function on Attention in the Lower Visual Field during Step Initiation , 2005, Gerontology.

[8]  Halla B. Olafsdottir,et al.  The emergence and disappearance of multi-digit synergies during force-production tasks , 2005, Experimental Brain Research.

[9]  R. Lepers,et al.  The role of anticipatory postural adjustments and gravity in gait initiation , 2004, Experimental Brain Research.

[10]  M. Latash,et al.  Age-related changes in finger coordination in static prehension tasks. , 2004, Journal of applied physiology.

[11]  M L Latash,et al.  Anticipatory postural adjustments during self-initiated perturbations of different magnitude triggered by a standard motor action. , 1996, Electroencephalography and clinical neurophysiology.

[12]  Jack M. Winters,et al.  Multiple Muscle Systems , 1990, Springer New York.

[13]  M. Latash,et al.  Muscle synergies involved in shifting the center of pressure while making a first step , 2005, Experimental Brain Research.

[14]  M. Latash,et al.  Muscle synergies during shifts of the center of pressure by standing persons , 2003, Experimental Brain Research.

[15]  Vladimir M. Zatsiorsky,et al.  Finger interaction during accurate multi-finger force production tasks in young and elderly persons , 2004, Experimental Brain Research.

[16]  F. Horak,et al.  Influence of instruction, prediction, and afferent sensory information on the postural organization of step initiation. , 1996, Journal of neurophysiology.

[17]  Vladimir M. Zatsiorsky,et al.  Anticipatory covariation of finger forces during self-paced and reaction time force production , 2005, Neuroscience Letters.

[18]  Vladimir M. Zatsiorsky,et al.  Muscle synergies during shifts of the center of pressure by standing persons , 2003, Experimental Brain Research.

[19]  T Richard Nichols,et al.  Musculoskeletal mechanics: a foundation of motor physiology. , 2002, Advances in experimental medicine and biology.

[20]  M. Latash,et al.  Anticipatory postural adjustments during self-paced and reaction-time movements , 1998, Experimental Brain Research.

[21]  Itshak Melzer,et al.  The Effect of a Cognitive Task on Voluntary Step Execution in Healthy Elderly and Young Individuals , 2004, Journal of the American Geriatrics Society.

[22]  Noriyoshi Yamashita,et al.  Anticipatory control in the initiation of a single step under biomechanical constraints in humans , 2003, Neuroscience Letters.

[23]  J. F. Soechting,et al.  Postural Hand Synergies for Tool Use , 1998, The Journal of Neuroscience.

[24]  M. Latash,et al.  Motor Control Strategies Revealed in the Structure of Motor Variability , 2002, Exercise and sport sciences reviews.

[25]  B. Maton,et al.  Voluntary toe-walking gait initiation: electromyographical and biomechanical aspects , 2002, Experimental Brain Research.

[26]  J. Hair.  Multivariate data analysis , 1972 .

[27]  T D Sanger,et al.  Human Arm Movements Described by a Low-Dimensional Superposition of Principal Components , 2000, The Journal of Neuroscience.

[28]  S. Bouisset,et al.  Segmental Movement as a Perturbation to Balance? Facts and Concepts , 1990 .

[29]  E. Bizzi,et al.  Muscle synergies encoded within the spinal cord: evidence from focal intraspinal NMDA iontophoresis in the frog. , 2001, Journal of neurophysiology.

[30]  Lena H Ting,et al.  A limited set of muscle synergies for force control during a postural task. , 2005, Journal of neurophysiology.

[31]  Jae Kun Shim,et al.  The human central nervous system needs time to organize task-specific covariation of finger forces , 2003, Neuroscience Letters.

[32]  Gregor Schöner,et al.  The uncontrolled manifold concept: identifying control variables for a functional task , 1999, Experimental Brain Research.

[33]  B E Maki,et al.  The control of lateral stability during rapid stepping reactions evoked by antero-posterior perturbation: does anticipatory control play a role? , 1999, Gait & posture.

[34]  J. Massion,et al.  Axial synergies during human upper trunk bending , 1998, Experimental Brain Research.

[35]  M W Rogers,et al.  Lateral stability during forward-induced stepping for dynamic balance recovery in young and older adults. , 2001, The journals of gerontology. Series A, Biological sciences and medical sciences.

[36]  F. Lacquaniti,et al.  Five basic muscle activation patterns account for muscle activity during human locomotion , 2004, The Journal of physiology.

[37]  N. A. Bernshteĭn.  The co-ordination and regulation of movements , 1967 .

[38]  S. Bouisset,et al.  Postural adjustments associated with rapid voluntary arm movements in patients with Parkinson's disease. , 1987, Advances in neurology.