Author and graduation date: Lauren Elizabeth CHABOT, March, 1998

Committee members: Jeanne F. Nichols (Chair), Donna Beshgetoor, James F. Sallis, Karen J. Calfas

Thesis title: Assessment of Physical Activity with the CSA Accelerometer: Laboratory vs. Field Measures Committee

The purpose of this study was to determine, in a field setting using the CSA accelerometer, ranges of physical activity, based on data in the 1996 Surgeon General's report, and to compare field data with previously gathered laboratory data. Thirty non-obese adults (mean age 28 + 4 years) were instructed, in randomized oreder, to "stroll," "walk briskly," and "jog at a comfortable pace" for 5 minutes each around a flat, outdoor, cork 400m track. Subjects wore three accelerometers, one inserted into a pouch secured by a waist strap around the hip, and another around their wrist and ankle. Data from minutes 2-4 were used for analysis. One-way repeated measures ANOVA indicated significant differences in CSA counts at each site across all three velocities (p<0.05). ANOVA also revealed a significant difference between the three velocities, indicating that the device was sensitive to changes in speed. Predicted hip counts from the laboratory equation were then compared with observed counts from the field. The predicted CSA counts over-estimated the measured counts at all three speeds (p<0.05). The velocity at which each subject walked and jogged was then converted to a MET value using metabolic equations. New cut-points for light (2-3.9 METs), moderate (4-7 METs), and vigorous (>7 METs) were calculated. These were 2,673-3,899, 3,964-5,900 and <5,901 counts, respectively. These data indicate that cut-points for MET levels established in the laboratory are not appropriate for use in an outdoor setting. Possible differences in the biomechanics of treadmill versus overland walking and running may explain the observed results.

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