Accelerometer-based estimates of PA were obtained using the Actigraph MTI (Manufacturing Technologies, Inc., Model 7164, Shalimar, FL). This uniaxial electromechanical accelerometer is designed to record vertical plane acceleration and deceleration at a frequency of 10 × s−1, and at a threshold of 0.033 × g. Additional specifications for this device are published elsewhere (24 ). A number of studies have demonstrated its durability, reliability, and validity in adults against criterion methods such as heart rate monitoring and indirect calorimetry (25 (link)-29 (link)). The accelerometers were attached to a belt worn around the waist with accelerometer placement on the right hip. The manufacturer recommended accelerometer placement on the hip because this site permits measurement of whole body movement, does not interfere with daily activities, and is the most frequently used site in epidemiological studies.
For each assessment, the MTI Actigraph was initialized and set to record data in 60-second epochs prior to placement on the subject. Subjects were instructed to wear the accelerometer for seven contiguous days during all waking hours, except during water activities. The following measures were obtained: number of days measured, registered time (hr/day), and average duration (min/day) spent in all health-enhancing PA intensities including MPA (3-6 METs), VPA (> 6 METs), and combined MVPA (≥ 3 METs). Validation studies demonstrating the accuracy and precision of the MTI Actigraph model 7164 against portable indirect calorimetry systems in adults (25 (link)-29 (link)) have reported different cutoff points due to the wide range of activity types and intensities used in the calibration studies. Guided by a recent review of calibration studies of accelerometer output for adults (30 ), we minimized sampling error by averaging the cutoff points reported by laboratory- and field-based calibration studies using the MTI Actigraph model 7164 (25 (link)-29 (link)) and applied the resulting cutoff points to discriminate between PA intensities. Moderate (3-6 METs) and vigorous (>6 METs) PA intensity cutoffs from these studies ranged from 1,809-2,430 and 5,725-6,403 counts per minute, respectively. The applied cutoff points for light, moderate, and vigorous PA intensities were accelerometer recordings of 100 to 2,224, 2,225 to 5,950, and > 5,950 counts per minute, respectively.
Leisure time PA and exercise habits within the previous three months were assessed using the Aerobics Center Longitudinal Study Physical Activity Questionnaire (ACLS), which has been described elsewhere (31 ). The ACLS elicits self-reports of the frequency (sessions/week) and duration (minutes/session) of activities such as walking, running, treadmill, cycling, swimming, aerobics, yoga, weight lifting, and other sports (e.g. golf, tennis, soccer). Descriptions of activities are provided inTable 2 .
For each assessment, the MTI Actigraph was initialized and set to record data in 60-second epochs prior to placement on the subject. Subjects were instructed to wear the accelerometer for seven contiguous days during all waking hours, except during water activities. The following measures were obtained: number of days measured, registered time (hr/day), and average duration (min/day) spent in all health-enhancing PA intensities including MPA (3-6 METs), VPA (> 6 METs), and combined MVPA (≥ 3 METs). Validation studies demonstrating the accuracy and precision of the MTI Actigraph model 7164 against portable indirect calorimetry systems in adults (25 (link)-29 (link)) have reported different cutoff points due to the wide range of activity types and intensities used in the calibration studies. Guided by a recent review of calibration studies of accelerometer output for adults (30 ), we minimized sampling error by averaging the cutoff points reported by laboratory- and field-based calibration studies using the MTI Actigraph model 7164 (25 (link)-29 (link)) and applied the resulting cutoff points to discriminate between PA intensities. Moderate (3-6 METs) and vigorous (>6 METs) PA intensity cutoffs from these studies ranged from 1,809-2,430 and 5,725-6,403 counts per minute, respectively. The applied cutoff points for light, moderate, and vigorous PA intensities were accelerometer recordings of 100 to 2,224, 2,225 to 5,950, and > 5,950 counts per minute, respectively.
Leisure time PA and exercise habits within the previous three months were assessed using the Aerobics Center Longitudinal Study Physical Activity Questionnaire (ACLS), which has been described elsewhere (31 ). The ACLS elicits self-reports of the frequency (sessions/week) and duration (minutes/session) of activities such as walking, running, treadmill, cycling, swimming, aerobics, yoga, weight lifting, and other sports (e.g. golf, tennis, soccer). Descriptions of activities are provided in
