Issues in accelerometer methodology: the role of epoch length on estimates of physical activity and relationships with health outcomes in overweight, post-menopausal women

Table 2 Accelerometer data^† expressed using 60 and 10 second (s) epoch intervals in WOMAN Study Participants at the 48 month follow-up visit (n = 102).

	60s epoch		10s epoch		Δ^††	t-value
	Mean (SD)	Range	Mean (SD)	Range
Inactivity: wear time^†††	.60 (0.08)	.36 - .79	.72 (0.07)	.50 - .86	-.11 (0.02)	-50.3*
Inactivity (0-99 ct), min/day	523.4 (79.0)	351.2 - 702.9	622.8 (71.2)	449.2 - 765.5	-99.4 (22.4)	-44.9*
Light Intensity (100-<2020 ct), min/day	315.0 (74.2)	167.1 - 572.9	200.1 (51.8)	98.8 - 388.8	114.9 (27.0)	43.0*
Moderate Intensity (2020-<5999 ct), min/day	26.1 (19.6)	.28 - 92.4	41.2 (21.7)	3.7 - 107.0	-15.0 (5.9)	-25.5*
Vigorous Intensity (≥5999 ct), min/day	.7 (2.8)	.05 - 15.7	1.2 (3.0)	.04 - 17.9	-.5 (0.63)	-8.1*
MVPA (≥2020 ct), min/day	26.9 (20.1)	.28 - 92.9	42.4 (22.4)	3.8 - 109.5	-15.5 (6.1)	-25.8*
Activity Bouts of MVPA (≥2020 ct), min/day	14.6 (16.3)	0 - 70.4	14.6 (16.3)	0 - 70.4	---	---

^†Data presented as mean (standard deviation)
^††Δ calculated as the difference between the mean time spent per day in a given intensity level using a 60 second epoch interval (i.e., current practice) minus the average time spent per day in a given intensity level using a 10 second epoch interval and then averaged for all participants.
^†††Presented as the ratio between inactivity and wear time.
*Paired t-tests were used to test the hypothesis of no difference in physical activity summary estimates between ActiGraph data collected as 10 or 60 second epochs; P < 0.0001

ISSN: 1479-5868