Short-term non-stationarity and the development of postural control

The stationarity of center of pressure time-series in upright quiet bipedal standing was examined in four groups: 3- and 5-year-old children, young student adults, and an elderly group that ranged in age from 62-92 years. The young adult group showed the least absolute motion in the center of pressure with the degree of motion increasing with the child and elderly age groups. Examination of the stationarity of the center of pressure time-series for each postural trial revealed that in the time domain every trial in every condition in each age group was non-stationary. This non-stationarity was present across all frequency segments of the center of pressure dynamic in the 5-year-old, student, and elderly groups. In the 3-year-old group was there was modest evidence of the non-stationarity in the time domain being differentially present across frequencies (approx. 10% of trials). These findings are consistent with the proposition that short-term bounded non-stationarity prevails in quiet upright bipedal stance across a wide range of the lifespan. This process of non-stationarity may be a reflection of adaptation in the development of the coordination and control of posture.