Where comparison was possible, the results of the current study where relatively high: 4–12% higher than those of De Smet et al (2001) who allowed only one attempt with each hand, and 8–14% higher than those of Molenaar et al (2010) where three attempts were allowed.

The study by Butterfield et al (2009) reported 4% lower to 6% higher scores. Besides differences in methods, the higher results may be a consequence of the ongoing trend in the Netherlands, ie, height is still increasing over the decades (Fredriks et al 2000). This is supported by data from Statistics Netherlands (Frenken 2007). Another factor that must be taken into consideration is that the Dutch population, and in particular those in the three most northern provinces, is known to be relatively tall (Frenken 2007). Besides including a large number of children, a relatively large PD 332991 geographical area was covered and both rural and urban schools were included to selleck screening library ensure a broad diversity and heterogeneity of participants. A vast number of different instruments are available to measure grip strength. The Jamar hand dynamometer was selected because most normative studies have used this device and therefore it allows data to be compared with other (and future) studies (Innes 1999, Roberts et al

2011). Moreover, besides having a high test-retest and inter-investigator reliability, it also has high reproducibility when used by children (Lindstrom-Hazel et al 2009, Mathiowetz et al 1984,

Roberts et al 2011, Van den Beld et al 2006). To ensure all children were measured in the same manner, and again to follow standardised methods, participants were measured according to the ASHT protocol (Innes 1999, Roberts et al 2011). However, we implemented three exceptions. First, for the 4 and 5 year olds, the handle of the device was else set to the first setting, which is considered to be less accurate than the second (Bechtol 1954, Boadella et al 2005, Firrell and Crain 1996, Hamilton et al 1994). These findings result from studies that focus on adults, and young children obviously have smaller hands. Therefore the distance to the handle of the device (3.8 cm) is relatively large compared to their average hand size (Bear-Lehman et al 2002). In practice, they could not reach the second setting adequately, and the first setting has also been used for adults with small hands (Ruiz-Ruiz et al 2002). Second, it is preferred to use the mean of three attempts (MacDermid et al 1994, Mathiowetz et al 1984). However, other studies showed that scoring fewer attempts, taking fewer attempts into consideration, or even using the maximum attempt, does not lead to significant differences compared with the mean of three attempts (Coldham et al 2006, Crosby and Wehbé 1994, Haidar et al 2004). Additionally, although fatigue does not seem to influence grip strength measurement in adults, we could not find any studies regarding this matter in children.