Spontaneous whole body rotations and classical dance expertise: how shoulder-hip coordination influences supporting leg displacements.

The link between supporting leg stability and individual trunk strategies used during spontaneous whole-body rotations was studied according to visual and kinesthetic imagery styles for classical dancers and untrained female participants. Shoulders-hip angles in the horizontal plane and supporting leg (SL) displacements were analyzed with three-dimensional kinematic at the beginning and end of the four turns, identified according to their SL (left vs. right) and turn direction (clockwise, CW vs. counterclockwise, CCW). To begin a turn in CCW on left SL, all the participants turned shoulders before hips (-25 degrees angle), p<0.01. Untrained participants yielded the reverse (+30 degrees angle) in CW - their non-preferred turn - whereas dancers maintained their trunk en bloc. In the turn slow down, in their preferred direction all the participants adopted en bloc behavior to avoid imbalance. Dancers kept this pattern in CCW but untrained participants separated shoulders and hips, p<0.01; on left SL (+20 degrees angle) hips finished before shoulders and on right SL (-25 degrees angle), shoulders finished before hips. Both mental imagery styles and spatial context link reduction of shoulder-hip angle and stability of SL. Daily expertise, not only dance training, facilitates the en bloc shoulder-hip coordination to maintain equilibrium.