Kinetic Analysis of the Lower Limb during the Pirouette in Ballet

1. 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

2. 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

3. Double Pirouette

4. 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.

5. 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

6. 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

7. 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

8. Results 3D markers 3D model with GRFs

9. knee flexors flex knee during turn hip flexors initiate turn knee extensors resist flexion plantiflexors later provide a small impulse before single support occurs Double turn (Fl/Ex) – trail leg

10. knee extensors initially resist flexion then help to extend limb hip extensors extend support limb then hip moments work isometrically plantiflexors provide a larger impulse just as single-support occurs Double turn (Fl/Ex) – stance leg

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

12. hip abductors initially resist adduction then knee abductors perform negative work ankle ab/adductors contribute little work before or during stance Double turn (Ab/Ad) – stance leg

13. All turns - Trail Leg (Fl/Ex) • greatest change occurs with the work done by the hip flexors of trail leg for double pirouette

14. All turns - Stance Leg (Fl/Ex) • no change in ankle work • hip extensors increased only for double pirouette

15. All turns - Stance Leg (Ab/Ad) • greatest changes occur with the negative work done by the hip abductors of stance leg

16. 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

17. 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

18. Questions?

19. Initial Stance • en dedans is a right turn to a left supporting leg or vice versa • from fourth position

20. Full-body 3D Marker Set