Ankle Accelerometry for Assessing Physical Activity Among Adolescent Girls: Threshold Determination, Validity, Reliability, and Feasibility.
OBJECTIVE
Ankle accelerometry allows for 24-hr data collection and improves data volume/integrity versus hip accelerometry. Using Actical ankle accelerometry, the purpose of this study was to (a) develop sensitive/specific thresholds, (b) examine validity/reliability, (c) compare new thresholds with those of the manufacturer, and (d) examine feasibility in a community sample (low-income, urban adolescent girls).


METHODS
Two studies were conducted with 6th- through 7th-grade girls (aged 10-14 years old): First was a laboratory study (n = 24), in which 2 Actical accelerometers were placed on the ankle and worn while measuring energy expenditure (Cosmed K4b2, metabolic equivalents [METs]) during 10 prescribed activities. Analyses included device equivalence reliability (intraclass correlation coefficient [ICC], activity counts of 2 Acticals), criterion-related validity (correlation, activity counts and METs), and calculations of sensitivity, specificity, kappa, and receiver-operating characteristic curves for thresholds. The second was a free-living study (n = 459), in which an Actical was worn for more than 7 days on the ankle (full 24-hr days retained). Analyses included feasibility (frequencies, missing data) and paired t tests (new thresholds vs. those of the manufacturer).


RESULTS
In the laboratory study, the Actical demonstrated reliability (ICC = .92) and validity (r = .81). Thresholds demonstrated sensitivity (91%), specificity (84%), kappa = .73 (p = .043), area under curve range = .81-.97. In the free-living study, 99.6% of participants wore the accelerometer; 84.1% had complete/valid data (mean = 5.7 days). Primary reasons for missing/invalid data included: improper programming/documentation (5.2%), failure to return device (5.0%), and wear-time ≤ 2 days (2.8%). The moderate-to-vigorous physical activity threshold (> 3,200 counts/minute) yielded 37.2 min/day, 2 to 4.5 times lower than that of the manufacturer's software (effect size = 0.74-4.05).


CONCLUSIONS
Validity, reliability, and feasibility evidences support Actical ankle accelerometry to assess physical activity in community studies of adolescent girls. When comparing manufacturers' software versus new thresholds, a major difference was observed.
a University of Maryland School of Medicine.
Erin R
ER
Hager
b University of Maryland Eastern Shore.
Margarita S
MS
Treuth
a University of Maryland School of Medicine.
Candice
C
Gormely
a University of Maryland School of Medicine.
LaShawna
L
Epps
a University of Maryland School of Medicine.
Soren
S
Snitker
a University of Maryland School of Medicine.
Maureen M
MM
Black
D061725:Accelerometry / Q000295:instrumentation*; D000293:Adolescent; D000294:Adolescent Behavior / Q000502:physiology*; D000842:Ankle; D000886:Anthropometry; D002153:Calorimetry, Indirect; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D009043:Motor Activity / Q000502:physiology*; D015203:Reproducibility of Results
Actical; African American; community studies; moderate-to-vigorous physical activity