MATTHEWS, C. E., P. S. FREEDSON, J. R. HEBERT, E. J. STANEK III, P. A. MERRIAM, and I. S. OCKENE. Comparing physical activity assessment methods in the Seasonal Variation of Blood Cholesterol Study. Med. Sci. Sports Exerc., Vol. 32, No. 5, pp. 976–984, 2000.
Purpose: This paper evaluated three measures of physical activity employed in the Seasonal Variation of Blood Cholesterol Study (Seasons), and it had two objectives: 1) To examine the laboratory validity of the Actillume activity monitor, and 2) To examine the relative validity of three 24-h physical activity recalls (24HR) in quantifying short-term physical activity behaviors.
Methods: Nineteen healthy middle-age adults completed seven activity trials (reading, typing, box moving, stepping, and walking (3.5, 4.25, 5.0 km·h−1)) while oxygen consumption and Actillume measures were obtained. ANOVA, linear regression, and a scatter plot were employed to examine the validity of the Actillume. In relative validity analyses of the 24HR in the Seasons study, participants (N = 481) completed two or three 24HR (MET-h·d−1) and a modified Baecke Questionnaire. A subset of the cohort (N = 41) wore the Actillume for 3–8 d (counts·min−1·d−1). The relative validity of the 24HR method was examined by comparison to these criterion measures.
Results: In laboratory validation analyses, the monitor was found to discriminate between sedentary and moderate intensity activities, changes in walking speed, and to account for 79% of the variance in oxygen consumption across sedentary and walking trials. In relative validity analyses, correlations between the 24HR and the modified Baecke ranged from 0.29 to 0.52 (P < 0.01) across total, household, occupational, and leisure-time activities.
Conclusions: In laboratory testing, the Actillume monitor discriminated between sedentary and moderate intensity activities and was highly correlated with oxygen consumption. Three 24HR of physical activity were observed to have a relative validity that was comparable to published data from other short-term activity assessments that also employed the Baecke Questionnaire and activity monitors as criterion measures.
Assessments of both diet and physical activity typically attempt to approximate “true” behavior within a given time period by assessing the behavior as it occurs (e.g., by diary), or by asking individuals to recall their behavior over periods ranging from the previous 24 h to many years (10,24,29). Physical activity and diet assessment instruments are susceptible to similar types of measurement errors; true random variation in the behavior (41), systematic reporting biases (6,19), errors in recalling past behavior (e.g., omission, intrusion, long-term averaging) (16,38), and errors in the translation of frequency and volume information into biochemical (diet) and energy expenditure (activity) values (1,41). Moreover, neither of the two behaviors has an easily administered “gold standard” that could be used to validate simpler and less time-consuming methods suitable for large-scale epidemiologic research.
The Seasonal Variation of Blood Cholesterol Study (Seasons) was a longitudinal study of 641 adults designed to quantify the magnitude and timing of seasonal changes in blood lipids and to identify the major factors contributing to this variation. These included dietary fat, physical activity, exposure to light, psychological variables, weather patterns, and changes in body mass. At baseline and in each of four subsequent quarters of follow-up, physical activity, diet, and light exposure data were collected using three 24-h recall (24HR) interviews. Additionally, a version of the Baecke physical activity questionnaire (5) modified to include household activity (40) was administered at baseline and one-yr of follow-up. To examine the relative validity of the 24HR physical activity and light exposure self-reports, a subsample of the Seasons population wore an Actillume physical activity and light exposure monitor (13,14) in each quarter of the study. To our knowledge, there are no published reports of the validity of the Actillume as a monitor of whole-body physical activity.
Multiple unannounced 24HR telephone diet interviews have emerged as a preferred assessment method because they appear to minimize overall error (9,12,20). Because of this, and to collect the dietary and physical activity data in the same time frame, the primary physical activity data in the Seasons study were collected using 24HR interviews. Although dietary data often have been collected using serial 24HR interviews, this method only rarely has been used to obtain physical activity data and is not often recognized as a viable data collection option.
Given the lack of data regarding the validity of the Actillume as a monitor of activity, and because the relative validity of the 24HR activity recall method was not known, the present paper presents the results of two experiments with the following purposes: 1) to examine the properties of the Actillume as a monitor of physical activity, specifically its ability to estimate energy expended in walking and other common activities and to discriminate between sedentary and moderate intensity activities; and 2) to examine the relative validity of three 24HR in estimating short-term physical activity behavior by using a modified Baecke questionnaire and Actillume as criterion measures.
University of Massachusetts Medical School and School of Public Health and Health Sciences, Worcester and Amherst, MA
Submitted for publication July 1998.
Accepted for publication August 1999.
Address for correspondence: Charles Matthews, Department of Epidemiology and Biostatistics, University of South Carolina, School of Public Health, Columbia, SC 29208; E-mail: email@example.com.