The Margin of Stability During a Single Turn Pirouette in Female Amateur Dancers: A Pilot Study

This study aimed to examine measures of dynamic balance during a single turn en dehors pirouette in healthy female amateur ballet dancers. Four participants performed pirouettes until five successful pirouettes were achieved without hopping or loss of balance. The center of mass (CoM), extrapolated center of mass (XCoM), center of pressure (CoP), and base of support (BoS) were determined using ground reaction forces recorded from floor-embedded force plates and the motion trajectories of anatomical reflective markers based on modified Plug-in Gait and Oxford Foot models. The CoM, XCoM, CoP, and BoS were determined throughout the turn phase using a laboratory and virtual left (LFT) foot coordinate system located in the dancer’s stance foot. Two calculations were used to measure the margin of stability (MoS), the distance between the: 1) XCoM and CoP and 2) XCoM and BoS. Both methods resulted in similar distances, with a smaller distance between the components along the antero-posterior axis (AP) of the virtual LFT foot coordinate system and a greater distance along the medio-lateral (ML) axis throughout the turn phase. Both measurements of the MoS demonstrated increased distances at the beginning and end of each turn, and the least distance during the middle of the turn phase. The topple angle was greater at the beginning and end of the turn phase and minimized during the middle period of the turn. Since this study included healthy dancers and only analyzed successful turns, the variability between trials within a dancer and across participants and trials was documented and showed moderate inter-trial and across-participant variations. Although our results are preliminary, they suggest that the MoS may be useful for detecting faults in the control of dynamic balance of dehors pirouette performance as part of training and rehabilitation following injury.