title: Development of infant leg coordination: Exploiting passive torques.
abstract: Leg joint coordination systematically changes over the first months of life, yet there is minimal data on the underlying change in muscle torques that might account for this change in coordination. The purpose of this study is to investigate the contribution of torque changes to early changes in leg joint coordination. Kicking actions were analyzed of 10 full-term infants between 6 and 15-weeks of age using three-dimensional kinematics and kinetics. We found 11 of 15 joint angle pairs demonstrated a change from more in-phase intralimb coordination at 6-weeks to less in-phase coordination at 15-weeks. Although the magnitude of joint torques normalized to the mass of the leg remained relatively consistent, we noted more complex patterns of torque component contribution across ages. By focusing on the change in torques associated with hip-knee joint coordination, we found that less in-phase hip-knee joint coordination at 15-weeks was associated with decreased influence of knee muscle torque and increased influence of knee gravitational and motion-dependent torques, supporting that infants coordinate hip muscle torque with passive knee gravitational and motion-dependent torques to generate kicks with reduced active knee muscle torque. We propose that between 6 and 15-weeks of age less in-phase hip-knee coordination emerges as infants exploit passive dynamics in the coordination of hip and knee motions.
authors.affiliation: Division of Biokinesiology & Physical Therapy, University of Southern California, 1540 E. Alcazar St., CHP 155, Los Angeles, CA 90033, USA. Electronic address: bsargent@usc.edu.
authors.forename: Barbara
authors.initials: B
authors.lastname: Sargent
authors.affiliation: Department of Physical Therapy and Biomechanics and Movement Sciences Program, University of Delaware, 307 McKinly Laboratory, Newark, DE 19716, USA.
authors.forename: John
authors.initials: J
authors.lastname: Scholz
authors.affiliation: Department of Kinesiology, Temple University, 1801 N. Broad Street, Philadelphia, PA, USA. Electronic address: tuf79669@temple.edu.
authors.forename: Hendrik
authors.initials: H
authors.lastname: Reimann
authors.affiliation: Department of Physical Therapy, Niigata University of Health and Welfare, 1398 Shimami Kitaku, Niigata 9503198, Japan. Electronic address: kubo@nuhw.ac.jp.
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Kubo
authors.affiliation: Division of Biokinesiology & Physical Therapy, Department of Pediatrics Keck School of Medicine, University of Southern California, 1540 E. Alcazar St., CHP 155, Los Angeles, CA 90033, USA. Electronic address: fetters@usc.edu.
authors.forename: Linda
authors.initials: L
authors.lastname: Fetters
mesh_terms: D001696:Biomechanical Phenomena; D005260:Female; D006112:Gravitation; D006621:Hip Joint / Q000502:physiology; D006801:Humans; D007223:Infant; D018730:Infant Behavior / Q000502:physiology*; D007596:Joints / Q000502:physiology; D007700:Kinetics; D007719:Knee Joint / Q000502:physiology; D007866:Leg / Q000502:physiology*; D008297:Male; D009038:Motion; D018482:Muscle, Skeletal / Q000502:physiology; D019415:Torque
keywords: Coordination; Infant; Kinematics; Kinetics; Motor control; Motor development