The vertical jump test was performed on an electronic mat connected to a digital timer that registered the total time in the air. From these data, the height of the jump in centimetres was automatically selleckchem calculated by the computer included in the standard equipment. All vertical jumps were performed from a standing position, and participants were first required to jump onto the mat with both feet, and then make a maximal vertical jump. Each subject performed three vertical jumps of which the highest jump (cm) was recorded. The intra-individual test variability, evaluated as the coefficient of variation for repeated measurements in 21 children, was 5.9%. Methodology of physical activity measurement has previously been presented in detail [1,15,16].

Physical activity was assessed using the MTI accelerometer, model 7164 for four consecutive days. Accelerometer data are averaged over a period of time called an epoch. A recording epoch of ten seconds was selected for this study. A SAS-based software was used to analyse all accelerometer data. This software automatically deletes missing data, defined as continuous sequences of 60 consecutive epochs (i.e. 10 minutes) or more with zero counts. This was done based on the assumption that all such sequences of zeroes lasting longer than ten minutes were caused by the accelerometer not being worn. In order to minimise inter-instrumental variation, all accelerometers were calibrated against a standardised vertical movement. Mean activity was considered to be the total accelerometer counts per valid minute of monitoring (mean counts/min).

Time spent performing above 3 METs was considered to reflect moderate to vigorous activity (MVPA), and time spent above 6 METs was considered to reflect vigorous activity (VPA). Cut-off points used for all children were > 167 counts/epoch for MVPA and > 583 counts/epoch for VPA [17,18]. Baseline measurements were performed at the commencement of school. Follow-up evaluations were done the same month one year later in the intervention group and two years later in the control group. Changes per 365 days were calculated. However, all the children stayed pre-pubertal in Tanner stage I during the study and pre-pubertal growth seems to be linear. One Swedish study reported that the growth rates in children are linear from age six to peak height velocity.

In girls peak height velocity is usually reached at a mean age of 11.7 years in Tanner stage III, whereas peak bone mineral accrual occurs at a mean age of 12.5 years in Tanner stage IV [19]. In boys both peak height velocity and peak bone mineral accrual are reached at an even higher age [19]. These observations are supported in Australian children Cilengitide [20], in which peak bone mass accrual and peak height velocity occurred in Tanner stage II or later, whereas the growth and bone mineral accrual were linear in Tanner stage I and during the ages followed in this study.