Assessing physical activity in persons with knee osteoarthritis using accelerometers: data from the osteoarthritis initiative.
OBJECTIVE
Physical activity measured by accelerometers requires basic assumptions to translate the output into meaningful measures. We used accelerometer data from the Osteoarthritis Initiative to investigate in the context of knee osteoarthritis (OA) the following data processing assumptions derived from the general US adult population: nonwear (a period the monitor was removed), based on zero activity exceeding 60 minutes; and a valid day of monitoring, based on wear time evidence exceeding 10 hours.


METHODS
We examined the influence of nonwear thresholds ranging from 20 to 300 minutes of zero activity on mean daily activity minutes (counts>0), mean daily activity counts, and mean daily moderate to vigorous physical activity minutes. The effect of selecting minimums of 8, 10, or 12 wear hours to signify a valid day of monitoring on data retention was examined.


RESULTS
Our sample of 3,536 days of accelerometer data from 519 persons with knee OA showed that mean daily activity minutes increased with the nonwear threshold until stabilizing at 463 minutes per day, corresponding to the 90-minute nonwear threshold. Similar patterns were observed for mean daily activity counts. Varying the nonwear threshold had no effect on mean daily moderate to vigorous physical activity minutes. Choosing the 90-minute nonwear threshold and a minimum of 10 wear hours to constitute a valid day provided 94% data retention.


CONCLUSIONS
Data supported applying the 90-minute nonwear threshold to the knee OA population instead of the 60-minute threshold for the general population, while retaining the 10-hour valid day threshold.
Song
Jing
J
Northwestern University Feinberg School of Medicine, Institute for Healthcare Studies, Chicago, Illinois 60611, USA. j-song1@northwestern.edu
Semanik
Pamela
P
Sharma
Leena
L
Chang
Rowland W
RW
Hochberg
Marc C
MC
Mysiw
W Jerry
WJ
Bathon
Joan M
JM
Eaton
Charles B
CB
Jackson
Rebecca
R
Kwoh
C Kent
CK
Nevitt
Michael
M
Dunlop
Dorothy D
DD
D000054:Acceleration; D000368:Aged; D018450:Disease Progression; D005080:Exercise Test / Q000295:instrumentation*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D020370:Osteoarthritis, Knee / Q000175:diagnosis / Q000503:physiopathology*; D011446:Prospective Studies; D015203:Reproducibility of Results; D012720:Severity of Illness Index
Arthritis Rheum. 2006 Apr 15;55(2):248-55
16583415
J Rheumatol. 2006 Nov;33(11):2271-9
17013996
J Appl Physiol (1985). 1997 Dec;83(6):2112-22
9390989
Med Sci Sports Exerc. 2010 Aug;42(8):1493-501
20139792
Med Sci Sports Exerc. 2007 Sep;39(9):1501
17805080
Arthritis Rheum. 2003 Dec;48(12):3359-70
14673987
Med Sci Sports Exerc. 2000 May;32(5):1018-23
10795795
Med Sci Sports Exerc. 2005 Nov;37(11 Suppl):S544-54
16294117
J Rheumatol. 2006 May;33(5):939-45
16652424
MMWR Morb Mortal Wkly Rep. 2007 May 4;56(17):423-5
17476205
Psychol Bull. 1968 Oct;70(4):213-20
19673146
J Clin Epidemiol. 2002 Apr;55(4):392-9
11927208
Am J Clin Nutr. 2002 Mar;75(3):519-25
11864858
Am J Clin Nutr. 2004 May;79(5):851-6
15113725
Arthritis Rheum. 2008 Sep 15;59(9):1229-36
18759320
Med Sci Sports Exerc. 2008 Jan;40(1):181-8
18091006
Med Sci Sports Exerc. 2002 Aug;34(8):1376-81
12165695
Int J Sports Med. 2003 May;24(4):298-303
12784173
Arthritis Rheum. 2004 Feb;50(2):624-8
14872507
Med Sci Sports Exerc. 2005 Nov;37(11 Suppl):S512-22
16294114
Am J Clin Nutr. 2002 Nov;76(5):935-41
12399263
Med Sci Sports Exerc. 2004 Sep;36(9):1637-45
15354049
Arthritis Rheum. 2008 Jun 15;59(6):849-56
18512720
Med Sci Sports Exerc. 1998 May;30(5):777-81
9588623
Med Sci Sports Exerc. 2003 Aug;35(8):1447-54
12900703
Med Sci Sports Exerc. 1994 Dec;26(12):1516-23
7869887