Nonstationary properties of postural sway

• Published in: Journal of biomechanics Vol. 26; no. 4; pp. 409 - 416
• Main Authors: Carroll, James P., Freedman, William
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.04.1993; Elsevier Science
• Subjects: Adult; Biological and medical sciences; Biomechanical Phenomena; Foot - physiology; Fundamental and applied biological sciences. Psychology; Humans; Male; Middle Aged; Motion; Postural Balance - physiology; Posture - physiology; Pressure; Space life sciences; Time Factors; Vertebrates: body movement. Posture. Locomotion. Flight. Swimming. Physical exercise. Rest. Sports; Biomechanics; Human; Orthostatism; Oscillation; Posture
• ISSN: 0021-9290; 1873-2380
• DOI: 10.1016/0021-9290(93)90004-X

Postural sway during quiet stance is usually assumed to be a stationary stochastic process. We tested this assumption by investigating the time invariance of the average value and variance of the postural sway of three subjects. The sway was measured with a force plate under three conditions: subject standing on two feet with eyes open; subject standing on two feet with eyes closed; and subject standing on one foot with eyes open. Data were collected in 1 min runs. More than 50 min of data were collected for each subject under each test condition. The data were averaged across all runs for each subject and condition. Trends were found to be present in the data. In addition, there were initial transient increases in the second-order moments about the trends. The transient changes in first- and second-order moments usually disappeared during the first 20 s. In light of these findings, we can reject the hypothesis that postural sway is a stationary process. The results imply that the usual methods to parameterize postural sway have to be either changed or reinterpreted.