Stadiometer

Children's weight and height were measured in duplicate by a trained experimenter. Children were weighed to the nearest 0.1 kg using a digital scale (PHARO 200, Soehnle, Benfeld, Germany) without shoes. Their length was measured to the nearest 0.1 cm using a stadiometer (TANITA Leicester, Birmingham, UK). Weight and height were transformed into BMI z-scores (BMIz) corrected for age and sex according to the WHO child growth reference for school-aged children and adolescents (36 (link)).

Each consenting child was measured without shoes or heavy outer garments by trained data collectors, in line with the Body Image Guidelines developed and endorsed by the OPAL Scientific Advisory Committee. Data collectors were trained in body image, cultural sensitivities, mandatory reporting and anthropometry; one data collector on the team was required to be a registered teacher. Height (Invicta Stadiometer) and weight (Tanita BWB-800 portable electronic scales) measures were taken by the same data collector on one occasion and final measures determined as the mean of two measures, or the median if three measures were taken (in the case that the first two measures differed by more than 0.5 cm or 0.5 kg, for height and weight respectively). Body Mass Index (BMI) was calculated as weight (kg) divided by height (m) squared and converted to age- and sex-specific z-scores using the UK 1990 reference data [32 (link)]. Children were categorised as underweight (BMI z score < − 1 to <− 3), normal weight (0), overweight (> 1.0 - < 2.0) or obese (> 2.0) using the International Obesity Taskforce (IOTF) cut-points [33 (link), 34 (link)].

Blood pressure was measured with an Omron sphygmomanometer twice in the right arm, with the subject seated and the arm supported. The mean of the two readings was used for analysis. With subjects in light clothing and without shoes, height was measured with a Harpenden stadiometer to the last complete 0.1 cm, and weight with a Tanita MA-418-BC body composition analyser (Tanita, Tokyo, Japan). Body mass index (BMI) was calculated as weight/(height)² (kg/m²). Grip strength (in kilograms) was measured using a Jamar Hydraulic Hand Dynamometer, with three measurements taken with each hand and the best of six used for the analysis. A walking test measured the time taken, in seconds, to walk 3 m at normal walking pace. A five-repetition sit-to-stand test was performed: participants were asked to move from a seated to a standing position five times in succession, avoiding the aid of hands and the time taken, in seconds, to perform this was recorded. Forced expiratory volume in 1 s (FEV1) was measured using a Vitalograph Compact II instrument with subjects standing, without nose clips. FEV1 was standardised to the average study height, 1.71 m, using the formula: standardised FEV1=FEV1 × (1.71/height)².