At 3- and 12-months postpartum, physical activity data were collected with a Manufacturing Technology Inc. (MTI) ActiGraph accelerometer (Pensacola, FL). The ActiGraph model #7164 is a small, light-weight uniaxial accelerometer that can be worn at the hip, ankle, or wrist. It measures accelerations in the range of 0.05 to 2 G’s with a band limited frequency of 0.25-2.5 Hertz (Trost et al., 2005 (link)). Validity of the monitor as an indicator for physical activity has been demonstrated among adults (Brage, Wedderkopp, Franks, Andersen, & Froberg, 2003 (link); Freedson, Melanson, & Sirard, 1998 (link); Hendelman, Miller, Baggett, Debold, & Freedson, 2000 (link)). The ActiGraph has also been shown to be a technically reliable instrument, able to detect differing levels of intensity (Brage, Brage, Wedderkopp, & Froberg, 2003 ; Brage, Wedderkopp et al., 2003 ; Esliger & Tremblay, 2006 (link); McClain, Sisson, & Tudor-Locke, 2007 (link); Metcalf, Curnow, Evans, Voss, & Wilkin, 2002 (link); Welk, Schaben, & Morrow Jr., 2004 (link)).
From November 2004 to January 2007, women participating in the PIN3 Postpartum Study were asked to wear the accelerometer for one week at the conclusion of their 3- and 12-month home visits. If they agreed, women were fitted with the accelerometer to be worn on a belt or clip-on pouch over their right hip at the iliac crest. Written and verbal instructions, as well as a phone number to call with questions, were provided. Participants mailed the monitor back to the study offices at the conclusion of the 7 days. In thanks for their time, women received $30 at 3-months postpartum and $40 at 12-months postpartum. ActiGraph accelerometer data were collected with 1-minute epochs, and the monitors were regularly calibrated throughout the study using the calibration machine from MTI. To convert accelerometer counts to a measure of intensity, we utilized ActiGraph cutpoints for moderate-to-vigorous activity provided in two studies of adults: Freedson et al (Freedson et al., 1998 (link)) cutpoint of 1952 counts per minute and Swartz et al (Swartz et al., 2000 (link)) cutpoint of 573 counts per minute. We also classified inactivity at a count of less than or equal to 100 counts per minute (Matthews et al., 2008 ).
From November 2004 to January 2007, women participating in the PIN3 Postpartum Study were asked to wear the accelerometer for one week at the conclusion of their 3- and 12-month home visits. If they agreed, women were fitted with the accelerometer to be worn on a belt or clip-on pouch over their right hip at the iliac crest. Written and verbal instructions, as well as a phone number to call with questions, were provided. Participants mailed the monitor back to the study offices at the conclusion of the 7 days. In thanks for their time, women received $30 at 3-months postpartum and $40 at 12-months postpartum. ActiGraph accelerometer data were collected with 1-minute epochs, and the monitors were regularly calibrated throughout the study using the calibration machine from MTI. To convert accelerometer counts to a measure of intensity, we utilized ActiGraph cutpoints for moderate-to-vigorous activity provided in two studies of adults: Freedson et al (Freedson et al., 1998 (link)) cutpoint of 1952 counts per minute and Swartz et al (Swartz et al., 2000 (link)) cutpoint of 573 counts per minute. We also classified inactivity at a count of less than or equal to 100 counts per minute (Matthews et al., 2008 ).
