Grip strength was measured using the Jamar® hydraulic hand dynamometera. A total of six calibrated dynamometers were at the researchers’ disposal. The devices were replaced twice, at subsequent time intervals, with two used devices exchanged for two non-used devices after approximately one-third, and again after two-thirds of the total number of children we aimed to recruit had been assessed. The following standardised testing position for measuring grip strength was used, as advocated by the American Society of Hand Therapists (ASHT): the participant

is seated with shoulders adducted and neutrally rotated, elbow flexed at 90 deg, wrist between 0 and 30 deg extension, and between 0 and 15 deg ulnar deviation (Balogun BIBF 1120 research buy et al 1985, Fess 1992). The handle of the device was set to the second position buy GSK1349572 for all participants, with the exception of 4 and 5 year olds, for whom the bar was set to the first position, and who were allowed to manually support the arm with the other hand. Participants were allowed four attempts using the dynamometer, two with each hand, and each individual attempt was scored. The starting hand was alternated between subjects and a 10-sec break was allowed between attempts. A Dutch translation of the Southampton grip strength measurement protocol was used as verbal encouragement (Roberts et al 2011). Encouragement was kept as consistent as possible

for every participant in volume and tone, counting down from 3 to 0, followed by ‘squeeze as hard as you can … squeeze and let go’. Descriptive statistics were used to describe the main characteristics of the participants. The Mann-Whitney U test was used to compare grip strength between genders. In order to establish

the correlation of gender, age, height, and weight with grip strength in more detail, we performed a multilevel analysis adding them as fixed factors. As intercept, the school the child attended was added. Results were accepted to be significant PD184352 (CI-1040) when the p value was < 0.05. In total 19 schools participated, located in 12 towns and cities. Thirteen children were ineligible for participation in the study. Two children were excluded because of Down syndrome, two children because they suffered from active juvenile arthritis, four because they had pre-existing pain of a hand or arm, and one because she received hormonal therapy to improve growth. Another four children were excluded because they did not meet the inclusion criteria, but no specific reason was recorded. Nine eligible children were excluded because the form on which measurements were written was not filled in completely. In order to get an impression of how many children refused to participate we randomly recorded the number of children that refused to participate at half of the schools visited. Based on this registration it can be estimated that about 1% of invited children did not participate in the study.