title: Two-thirds power law in human locomotion: role of ground contact forces.
abstract: Are there general rules for the generation of curvilinear motion of the end-effector? Form and kinematics of the arm trajectory are typically inter-related. A relationship between velocity and curvature of the endpoint path has been previously described and quantified as the two-thirds power law. Here we show that the two-thirds power law holds also for the foot trajectory (during the swing phase) in human locomotion for a wide range of walking speeds and gravitational loads, but air-stepping. In air-stepping, it was violated systematically. The results suggest that the power law represents a general constrain of biological motion, may be attributed to both mechanical and neural factors and can depend on natural interactions with external environment.
authors.affiliation: Sezione di Fisiologia Umana, Istituto Scientifico Fondazione Santa Lucia, via Ardeatina 306, 00179 Rome, Italy.
authors.forename: Yuri P
authors.initials: YP
authors.lastname: Ivanenko
authors.forename: Renato
authors.initials: R
authors.lastname: Grasso
authors.forename: Velio
authors.initials: V
authors.lastname: Macellari
authors.forename: Francesco
authors.initials: F
authors.lastname: Lacquaniti
mesh_terms: D000328:Adult; D002490:Central Nervous System / Q000502:physiology; D005080:Exercise Test; D005260:Female; D005528:Foot / Q000502:physiology*; D005684:Gait / Q000502:physiology*; D006225:Hand / Q000502:physiology; D006801:Humans; D008124:Locomotion / Q000502:physiology*; D008297:Male; D010507:Periodicity; D011698:Pursuit, Smooth / Q000502:physiology; D012044:Regression Analysis; D016474:Weight-Bearing / Q000502:physiology