Table 1.

Examples of objective balance and gait metrics sensitive to PD that could provide biomarkers grouped by gait and balance impairments.

Neural Control Systems	Impairments	Task	Metrics from body-worn sensors
I. Postural Sway	Postural Instability	Quiet stance (≥30s)	Sway Velocity, Sway Area, Sway jerkiness,(25, 28, 29), Sway frequency (24)
II. Postural Responses	Ineffective stepping response	Push and Release	Latency, Step length, Number of steps, Time to Equilibrium (38)
III. Anticipatory Postural Adjustments (APA)	Impaired gait Initiation	Step Initiation	Lateral and Sagittal Peak APA (39)
IV. Gait
Dynamic Equilibrium	Gait Instability	Straight Walking at prefered gait speed	Stride Time Variability (14, 15, 58), Double Support Time (10, 14)
Upper Body Control	“En-bloc”		Peak arm velocity, Trunk Rotation (10)
Spatio-temporal Coordination	Slow gait		Gait Velocity, Cadence, Stride Length (10, 48, 63)
V. Postural Transitions	Difficulty changing motor programs	Timed-Up and Go	Turning Duration (10, 62, 63), Turning Jerk (62), Range and-to-Stand and Sit Stand-to-Sit Jerk (63)
VI. Unknown (66)	Freezing of Gait	Turn 360° degrees	Shank Frequency Ratio (65, 66, 68)