Kinetic Analysis of the Lower Limb during the Pirouette in Ballet

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					 Kinetic Analysis of the Lower Limb
    during the Pirouette in Ballet

D. Gordon E. Robertson, PhD, FCSB
Cristina Fulop
Tama Davis
Courtney Timm

Biomechanics, Laboratory,
School of Human Kinetics,
University of Ottawa, Ottawa, Canada
              Introduction

• pirouette is a basic ballet skill that involves
  spin about the vertical axis while in single
  support
• can be done with 1, 2 or 3 turns from a two-
  foot stance
• more turns (fouetté) require additional
  motions of the free leg
• very little data exists in literature concerning
  how this maneuver is performed
Double Pirouette
                 Review

• Laws (1978) used a turntable with large
  moment of inertia to indirectly measure total
  body angular momentum of pirouettes en
  dedans and en dehors and an arabesque turn.
• Laws (2002) outlined the various categories
  of pirouettes (en dedans, en dehors etc.) and
  suggested that the torque necessary for
  creating the spin comes from a force couple
  created by the two feet.
• He had no data to support this concept.
                Purpose

• to identify the net moments of force using
  inverse dynamics that create the pirouette
• to examine how moments of force change as
  the number of turns increases
• to determine the roles of the stance and
  swing legs during the pirouette
                Methods
• one female subject with 10 years training
• full-body (49) marker set (extension of
  Vicon’s plug-in gait)
• seven Vicon MX13 cameras sampling at
  200 fps
• two force platforms (Kistler) sampled at
  1000 Hz
• 5 trials each from fourth position
   – half turns
   – full turns
   – double turns
                 Methods

• processed with Visual3D
• 3D moments computed bilaterally at ankles,
  knees and hips
• moment powers computed from products of
  joint angular velocities and moments of force
            PM = M w
             Results




3D markers         3D model with GRFs
          Double turn (Fl/Ex) – trail leg
                              knee extensors resist flexion
plantiflexors later provide       knee flexors flex knee
  a small impulse before            during turn
  single support occurs             hip flexors initiate turn
       Double turn (Fl/Ex) – stance leg
                           knee extensors initially
                             resist flexion then help
plantiflexors provide a      to extend limb
  larger impulse just as                  hip extensors extend
  single-support occurs                     support limb then
                                            hip moments work
                                            isometrically
        Double turn (Ad/Ad) – trail leg

ankle abductors do small   hip abductors do small
  amount of negative         amount of work with
  work                       no work done at knee
    Double turn (Ab/Ad) – stance leg

ankle ab/adductors          hip abductors initially
  contribute little work      resist adduction then
  before or during stance     knee abductors perform
                              negative work
         All turns - Trail Leg (Fl/Ex)
• greatest change
  occurs with the
  work done by the
  hip flexors of
  trail leg for
  double pirouette
        All turns - Stance Leg (Fl/Ex)
• no change in
  ankle work
• hip extensors
  increased only
  for double
  pirouette
       All turns - Stance Leg (Ab/Ad)
• greatest
  changes occur
  with the
  negative work
  done by the hip
  abductors of
  stance leg
              Discussion

• torque during a pirouette is created by trail
  leg initiating a moment while support leg
  applies resistance, not by a force couple
• support leg lifts dancer en pointe or demi
  pointe once single support occurs
• during single support, trail (gesture) leg
  flexes to reduce the body’s moment of inertia
  and thereby increase spin rate
• arms main purpose was to increase and
  decrease body’s moment of inertia, first to
  increase angular momentum then to increase
  and decrease spin rate
              Discussion

• when increasing number of spins main
  changes were:
   – trail leg hip flexors
   – stance hip extensors
   – stance hip abductors
• almost no change in trail leg push-off
• shoulder work increases for double
  turn
Questions?
             Initial Stance

• en dedans is a
  right turn to a
  left supporting
  leg or vice versa
• from fourth
  position
Full-body 3D Marker Set

				
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posted:2/7/2012
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