Validity of wrist worn accelerometers and comparability between hip and wrist placement sites in estimating physical activity behaviour in preschool children

Wrist-worn accelerometers can increase compliance with wearing accelerometers, however, several large scale studies continue to use hip-worn accelerometers and it is unclear how comparable data is from the two sites. The study aims were: to investigate agreement between wrist-and hip-worn accelerometers and to determine the validity of Johansson et al cut-points for wrist worn accelerometers in preschool children. A sample of 32 preschool children (21 boys, 4.2 (0.5) years, BMI 16.6 (1.1)) were videoed wearing GT3X+ accelerometers on their wrist and hip while they engaged in 1 h of free-play in their nursery. Children's activity were coded using, the children's activity rating scale (CARS): with CARS, level 1 'sedentary' and levels 2-5 were classified as time spent in total physical activity (TPA). Accelerometry data were processed using Johansson et al cut-points for the wrist data and Evenson et al cut-points for the hip data, into time spent in different intensities of physical activity (PA). The mean counts per minute (cpm) from the hip and wrist were compared. There was a strong correlation between the hip and wrist cpm (r = 0.81, p < 0.01) and total count data (r = 0.83 p < 0.01), however there was a large systematic bias with wide limits of agreement. Good agreement (mean difference (LOA) 1.1 (-9.9, 12.1) was found between the CARS estimate of TPA (29.5 (10.4) mins) and the wrist estimate, using the Johansson et al cut points (28.4 (9.8) mins). There was also a reasonable agreement between the hip estimates with the Evenson et al cut-points and Johansson et al estimate (mean difference (LOA): 6.3 (-8.8, 21.4) mins. In conclusion, the findings suggest that the Johansson et al (2013 Pediatr. Obes. 10 1-6) cut-points applied to wrist worn accelerometers provides a valid estimate of TPA in preschool children and have reasonable agreement with Evenson et al cut-points applied to hip accelerometers.