Reactivity in baseline accelerometer data from a physical activity behavioral intervention.
OBJECTIVE
This brief report describes the possibility of reactivity in the baseline assessment of physical activity using accelerometry from two separate randomized controlled trials of a behavior intervention for increasing physical activity in persons with multiple sclerosis (MS).


METHODS
The samples included 18 persons with multiple sclerosis (MS) from Study 1 and 20 from Study 2 who were randomized into treatment arms of the intervention. The participants initially wore an accelerometer over a 7-day period for collection of baseline data, and one week later wore a pedometer over a 7-day period for collection of data for self-monitoring and goal setting in week 1 of the 12-week intervention. The accelerometer and pedometer data were both expressed in average steps per day over a 7-day period.


RESULTS
There was a moderate (d = .56), statistically significant (p = .03) difference of 1,822 steps per day between baseline and week 1 of the intervention in Study 1. There was a large (d = 1.36), statistically significant (p = .0001) difference of 2,338 steps per day in Study 2.


CONCLUSIONS
We are unaware of other research describing a significant change in physical activity between baseline and the first week of a behavioral intervention and believe that this change reflects reactivity in the baseline assessment using accelerometry.
Department of Kinesiology and Community Health, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA. robmotl@illinois.edu
Robert W
RW
Motl
Edward
E
McAuley
Deirdre
D
Dlugonski
D056044:Actigraphy / Q000379:methods*; D000328:Adult; D001521:Behavior Therapy; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000503:physiopathology* / Q000628:therapy; D012016:Reference Values; D057566:Self Report; D016138:Walking