title: Lower extremity control during turns initiated with and without hip external rotation.
abstract: The pirouette turn is often initiated in neutral and externally rotated hip positions by dancers. This provides an opportunity to investigate how dancers satisfy the same mechanical objectives at the whole-body level when using different leg kinematics. The purpose of this study was to compare lower extremity control strategies during the turn initiation phase of pirouettes performed with and without hip external rotation. Skilled dancers (n=5) performed pirouette turns with and without hip external rotation. Joint kinetics during turn initiation were determined for both legs using ground reaction forces (GRFs) and segment kinematics. Hip muscle activations were monitored using electromyography. Using probability-based statistical methods, variables were compared across turn conditions as a group and within-dancer. Despite differences in GRFs and impulse generation between turn conditions, at least 90% of each GRF was aligned with the respective leg plane. A majority of the net joint moments at the ankle, knee, and hip acted about an axis perpendicular to the leg plane. However, differences in shank alignment relative to the leg plane affected the distribution of the knee net joint moment when represented with respect to the shank versus the thigh. During the initiation of both turns, most participants used ankle plantar flexor moments, knee extensor moments, flexor and abductor moments at the push leg׳s hip, and extensor and abductor moments at the turn leg׳s hip. Representation of joint kinetics using multiple reference systems assisted in understanding control priorities.
authors.affiliation: Department of Biomedical Engineering, University of Southern California, 3616 Trousdale Parkway, Los Angeles, CA 90089, USA. Electronic address: zaferiou@alumni.usc.edu.
authors.forename: Antonia M
authors.initials: AM
authors.lastname: Zaferiou
authors.affiliation: Department of Aerospace and Mechanical Engineering, University of Southern California, OHE 430E, Los Angeles, CA 90089, USA. Electronic address: hflashne@usc.edu.
authors.forename: Henryk
authors.initials: H
authors.lastname: Flashner
authors.affiliation: Department of Psychology, University of Southern California, 3620 South McClintock Ave., SGM501, Los Angeles, CA 90089, USA. Electronic address: rwilcox@usc.edu.
authors.forename: Rand R
authors.initials: RR
authors.lastname: Wilcox
authors.affiliation: Department of Biomedical Engineering, University of Southern California, 3616 Trousdale Parkway, Los Angeles, CA 90089, USA; Department of Biological Sciences, University of Southern California, 3616 Trousdale Parkway, AHF-252, Los Angeles, CA 90089, USA. Electronic address: mcnitt@usc.edu.
authors.forename: Jill L
authors.initials: JL
authors.lastname: McNitt-Gray
mesh_terms: D000328:Adult; D000843:Ankle Joint / Q000502:physiology; D001696:Biomechanical Phenomena; D004576:Electromyography; D005260:Female; D006615:Hip / Q000502:physiology*; D006801:Humans; D007719:Knee Joint / Q000502:physiology; D055595:Mechanical Phenomena; D018482:Muscle, Skeletal / Q000502:physiology; D012399:Rotation
keywords: Biomechanics; Dance; Joint kinetics; Reference systems; Turn