Modulation of Phasic and Tonic Muscle Synergies With Reaching Direction and Speed

• Published in: Journal of neurophysiology Vol. 100; no. 3; pp. 1433 - 1454
• Main Authors: d'Avella, Andrea, Fernandez, Laure, Portone, Alessandro, Lacquaniti, Francesco
• Format: Journal Article
• Language: English
• Published: United States Am Phys Soc 01.09.2008
• Subjects: Adult; Analysis of Variance; Biomechanical Phenomena; Electromyography - methods; Female; Humans; Male; Movement - physiology; Muscle, Skeletal - physiology; Postural Balance; Posture; Psychomotor Performance - physiology; Range of Motion, Articular - physiology; Recruitment, Neurophysiological; Time Factors
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.01377.2007

1 Department of Neuromotor Physiology, Santa Lucia Foundation; 2 Department of Neuroscience and 3 Center of Space Biomedicine, University of Rome Tor Vergata, Rome, Italy; and 4 Institute of Movement Sciences, University of Mediterranean, Marseille, France Submitted 20 December 2007; accepted in final form 30 June 2008 How the CNS masters the many degrees of freedom of the musculoskeletal system to control goal-directed movements is a long-standing question. We have recently provided support to the hypothesis that the CNS relies on a modular control architecture by showing that the phasic muscle patterns for fast reaching movements in different directions are generated by combinations of a few time-varying muscle synergies: coordinated recruitment of groups of muscles with specific activation profiles. However, natural reaching movements occur at different speeds and require the control of both movement and posture. Thus we have investigated whether muscle synergies also underlie reaching at different speeds as well as the maintenance of stable arm postures. Hand kinematics and shoulder and elbow muscle surface EMGs were recorded in five subjects during reaches to eight targets in the frontal plane at different speeds. We found that the amplitude modulation of three time-invariant synergies captured the variations in the postural muscle patterns at the end of the movement. During movement, three phasic and three tonic time-varying synergies could reconstruct the time-normalized muscle pattern in all conditions. Phasic synergies were modulated in both amplitude and timing by direction and speed. Tonic synergies were modulated only in amplitude by direction. The directional tuning of both types of synergies was well described by a single or a double cosine function. These results suggest that muscle synergies are basic control modules that allow generating the appropriate muscle patterns through simple modulation and combination rules. Address for reprint requests and other correspondence: A. d'Avella, Dipartimento di Fisiologia Neuromotoria, Istituto di Ricovero e Cura a Carattere Scientifico Fondazione Santa Lucia, Via Ardeatina 306, 00179 Rome, Italy (E-mail: a.davella{at}hsantalucia.it )