2008 Research Consortium Graduate Student Award Winners

Participation in moderate-to-vigorous physical activity (MVPA) is associated with many health benefits (Pate et al., 1995; U.S. Department of Health and Human Services, 1996). While it is critical, for public health research and policy decision making purposes, to determine the percentage of people in the U.S. who meet the physical activity (PA) recommendation, it has been difficult to assess, especially in free-living conditions, at the population level. In the past, determining the population’s PA participation was based mainly on self-report physical activity questionnaire (PAQ) data. Typically, information about the reported frequency, duration, and intensity of PA is summarized for a given period to determine a participant’s PA status according to a selected PA recommendation. However, self-report PAQs are subjective measures and are prone to recall bias. Respondents also tend to overreport their PA participations due to social norms. Recently, the National Health and Nutrition Examination Survey (NHANES) started to use ActiGraph AM-7164 (ActiGraph, Fort Walton Beach, FL), a type of accelerometer, to objectively measure PA. Participants were asked to wear the ActiGraph monitor on an elastic waist belt over their right hip for 7 consecutive days during normal waking hours, except for swimming and bathing. The recorded information (i.e., activity count per minute) was then recoded to the minutes of PA at different intensity levels according to predetermined cutoff points. There is inconsistency, however, in setting cutoff scores when determining MVPA due to different ActiGraph thresholds being used in practice (Ham et al., 2007). For example, the cutoff points from the Freedson, Melanson, and Sirard (1998) method are ≥ 1,952 counts•min-1 for moderate-to-high intensity and ≥ 5,725 for vigorous intensity, whereas they are 190.7 and 7,525.8 for the Hendelman, Miller, Baggett, Debold, and Freedson, (2000) method and 574 and 4,945 for the Swartz et al. (2000) method, respectively. Similarly, different cutoff scores were used in survey methods. For example, Kruger, Yore, and Kohl (2007) used 150 min/week for MVPA or 60 min/week for vigorous PA, and Blair, Kohl, and Gordon (1992) and Corbin, Pangrazi, and Welk (1994) used 3 kcal/kg/day for MVPA. Because of the inconsistency, the results may vary when different cutoff points are used. Determining PA status may also vary widely between self-report PAQ and objective measures from motion sensors. So far, little has been done using population data to investigate the classification agreement when different methods are used to determine the proportion of people who meet the PA recommendation. The purpose of this study was to compare the agreement among five different methods (three ActiGraph counts-based methods and two surveybased methods) to determine whether U.S. adults meet or do not meet the PA recommendation. A NHANES 2003–04 data subset (including demographics, PA questionnaire, PA individual activity, and PA activity monitor information) from adults ages 20 years or older was analyzed (unweighted N = 5,041; men = 48%, women = 52%). The three sets of ActiGraph cutoff points of moderate-to-vigorous and vigorous intensity levels were based on the methods of Freedson et al. (1998), Hendelman et al. (2000), and Swartz et al. (2000), and the two survey-based methods used those of Kruger et al. (2007), Blair et al. (1992), and Corbin et al. (1994). Participants were classified as: meet or do not meet the PA recommendation: For cutoff points methods, the PA activity monitor data were used in which the raw activity count•min-1 data were first processed using the SAS code posted on the NHANES web site (http://riskfactor.cancer.gov/tools/ nhanes_pam/) to determine valid and invalid ActiGraph information. The ActiGraph data were considered valid when the participant wore the device for 10 or more hours per day for at least 4 days during the data collec-