Location, Location, Location: Accelerometer Placement Affects Steps-Based Physical Activity Outcomes During Pregnancy and Postpartum

As pregnancy progresses, physical changes may affect physical activity (PA) measurement validity. n = 11 pregnant women (30.1 ± 3.8 years) wore ActiGraph GT3X+ accelerometers on the right hip, right ankle, and non-dominant wrist for 3-7 days during the second and third trimesters (21 and 32 weeks, respectively) and 12 weeks postpartum. Data were downloaded into 60-second epochs from which stepping cadence was calculated; repeated-measures analysis of variance was used to determine significant differences among placements. At all time points, the wrist accelerometer measured significantly more daily steps (9930-10 452 steps/d) and faster average stepping cadence (14.5-14.6 steps/min) than either the hip (4972-5944 steps/d, 7.1-8.6 steps/min) or ankle (7161-8205 steps/d, 10.3-11.9 steps/min) placement, while moderate- to vigorous-intensity activity at the wrist (1.2-1.7 min/d) was significantly less than either hip (3.0-5.9 min/d) or ankle (6.1-7.3 min/d). Steps, cadence, and counts were significantly lower for the hip than the ankle at all time points. Kappa calculated for agreement in intensity classification between the various pairwise comparisons ranged from .06 to .41, with Kappa for hip-ankle agreement (.34-.41) significantly higher than for wrist-ankle (.09-.11) or wrist-hip (.06-.16). These data indicate that wrist accelerometer placement during pregnancy likely results in over counting of PA parameters and should be used with caution.