Motor synergy organization during fatiguing single-leg heel-rise in young ballet dancers and non-dancers

The uncontrolled manifold (UCM) framework decomposes inter-trial kinematic variability into task-stabilizing (V_UCM) and task-destabilizing (V_ORT) components to quantify motor synergy organization. Whether long-term ballet training influences motor synergy structure during fatiguing lower-limb tasks remains unclear.

To what extent is long-term ballet practice related to the motor synergy organization that stabilizes the center of mass (COM) during a repetitive, fatiguing single-leg heel-rise task, compared with non-dancers?

Fourteen female ballet dancers (age: 23.3 ± 3.2 years; 14.9 ± 6.8 years of experience) and 15 female controls (age: 22.3 ± 2.4 years) performed a single-leg heel-rise task to volitional failure. Three-dimensional whole-body kinematics were recorded. UCM analysis was applied to the first and last 20 trials using 10 segment elevation angles and toe position coordinates as elemental variables and sagittal COM position as the performance variable. The synergy index (SI), V_UCM, and V_ORT were computed across five normalized movement phases. Group differences were analyzed using linear mixed-effects models.

The ballet group showed greater SI than the control group across all movement phases in both task blocks (ballet: 0.962-0.981; control: 0.831-0.931), with significant main effects of group at all phases (p < 0.05) and group-by-phase interactions at 60-80% and 80-100%. This was primarily driven by smaller V_ORT in the ballet group (significant group effect at all phases, p < 0.05).

Ballet practice is associated with reduced task-destabilizing variability during fatiguing heel-rise tasks, suggesting that ballet training may refine intersegmental coordination for COM stabilization.