title: Pilot study on quantitative assessment of muscle imbalance: differences of muscle synergies, equilibrium-point trajectories, and endpoint stiffness in normal and pathological upper-limb movements.
abstract: This paper proposes a novel method for assessment of muscle imbalance based on muscle synergy hypothesis and equilibrium point (EP) hypothesis of motor control. We explain in detail the method for extracting muscle synergies under the concept of agonist-antagonist (AA) muscle pairs and for estimating EP trajectories and endpoint stiffness of human upper limbs in a horizontal plane using an electromyogram. The results of applying this method to the reaching movement of one normal subject and one hemiplegic subject suggest that (1) muscle synergies (the balance among coactivation of AA muscle pairs), particularly the synergies that contributes to the angular directional kinematics of EP and the limb stiffness, are quite different between the normal subject and the hemiplegic subject; (2) the concomitant EP trajectory is also different between the normal and hemiplegic subjects, corresponding to the difference of muscle synergies; and (3) the endpoint (hand) stiffness ellipse of the hemiplegic subject becomes more elongated and orientation of the major axis rotates clockwise more than that of the normal subject. The level of motor impairment would be expected to be assessed from a comparison of these differences of muscle synergies, EP trajectories, and endpoint stiffness among normal and pathological subjects using the method.
authors.forename: Takanori
authors.initials: T
authors.lastname: Oku
authors.forename: Kanna
authors.initials: K
authors.lastname: Uno
authors.forename: Tomoki
authors.initials: T
authors.lastname: Nishi
authors.forename: Masayuki
authors.initials: M
authors.lastname: Kageyama
authors.forename: Pipatthana
authors.initials: P
authors.lastname: Phatiwuttipat
authors.forename: Keitaro
authors.initials: K
authors.lastname: Koba
authors.forename: Yuto
authors.initials: Y
authors.lastname: Yamashita
authors.forename: Kenta
authors.initials: K
authors.lastname: Murakami
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Uemura
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Hirai
authors.forename: Fumio
authors.initials: F
authors.lastname: Miyazaki
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Naritomi
mesh_terms: D000368:Aged; D001132:Arm / Q000503:physiopathology*; D001696:Biomechanical Phenomena; D004576:Electromyography; D005069:Evaluation Studies as Topic; D006429:Hemiplegia / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology; D018482:Muscle, Skeletal / Q000503:physiopathology; D010865:Pilot Projects; D020521:Stroke / Q000503:physiopathology