Gender difference in handgrip strength of Italian children aged 9 to 10 years

In this investigation we provided the maximum HGS value of apparently healthy Italian schoolchildren girls and boys aged 9 to 10 years. Furthermore, as expected, we demonstrated a significant difference in HGS performance between gender (Table 1). We also found an association between HGS and age, gender and anthropometric variables such as BMI, height and weight (Tables 2 and 3).

Our investigation is important since, currently, there is scarcity of data regarding the reference values for HGS in European children aged 9 to 10 years, especially Italian.

The availability of reference values assumes importance in a number of conditions. HGS is used as index of physical fitness in children [1‐4]. Physical activity plays a key role in the normal growth during the first phase of life and for the psycho-social maturation of the young [28] and physical fitness is a predictor of morbidity [1‐3]. HGS is a nutritional status index [8, 10, 29, 30] and is useful for investigating patients with neuromuscular disease [31]. Moreover, HGS is a predictor of mortality in youth [4]. Therefore, the availability of normative data for HGS could help to identify those children needing special dietary or pharmacological treatments or those at high risk of clinical complications [11‐14].

In line with other investigations, like EUROFIT [20] and CHMS [17], we measured the maximal HGS, while in the IDEFICS [18] and HELENA [19] studies the authors used the mean value between hands. However, both methods were found to be highly consistent with no statistically significant difference [27]. Our HGS values were similar to those of EUROFIT [20] and IDEFICS [18]. On the contrary, as expected, our result was very different from those of CHMS, performed in Canadian children with an HGS value between 24 and 27 kg in boys and between 21 and 24 in girls aged 8–10 years old [17]. This finding reinforces the importance of having a reference value for different populations.

An important finding of our investigation was the significantly greater maximal HGS in boys than in girls. In this regard, we found, in the whole population, an HGS value of 13.8 ± 4.0 in girls and 15.2 ± 3.0 kg in boys (Table 1). Our results were similar to those of the EUROFIT study, in which the maximal HGS was 14.1 ± 2 in girls and 15.7 ± 3 kg in boys at age 9 and 17.1 ± 3 in girls and 16 ± 3 kg in boys at age 10 [20]. Even in the CHMS, Helena and IDEFICS studies, a sex-dependent difference was found [17‐19]. Nevertheless it has been demonstrated that sex- and age- dependent differences in HGS disappears when HGS is normalised for fat-free mass [25], the most import factor influencing HGS seems to be still gender or, specifically, sex hormones. In fact, fat-free mass, in turn, is linked to the sex hormones and is more represented in boys than in girls [25]. In this regard, it is well known that sexual dimorphism in body composition is largely due to the action of sex steroid hormones [26]. An important concept is that sex difference in body composition is manifest from foetal life and, in children, a significant difference in estradiol and testosterone is evident before the external signs of puberty appear [32], probably leading to a difference in HGS. Interestingly, a specific sexually dimorphic response to maternal diet was observed in the placenta [33]. Placenta reacts differently to the same environment depending on the sex of the foetus [33, 34]. All together, these studies confirm the validity of our data and suggest a different response early in life between gender leading to a different body composition and HGS. According with this assumption, we did not find a significant difference in anthropometric parameters (height, body mass and BMI) between genders (Table 1).

Previous investigations demonstrated that HGS is positively correlated with weight, height and body surface area [23, 35] and that, in the early phase of puberty, body height could be a key factor influencing HGS [24]. Our results are in line with these previous findings. In fact, when we included in the multivariable analysis, as independent variable body height and weight, in place of BMI, the gender factor disappeared (Table 3). However, the height of children is considered an index of their sexual maturity [36]. Thus, again, the most import factor influencing HGS could be gender.

Also the age-dependent increase in HGS, previously described [18, 20] can be attributed to hormonal changes over time [37], nevertheless in boys, growth hormone and testosterone have more effects on HGS than in girls [37].

Our study highlights the need to have a reference value for HGS useful to plan interventions aimed at improving fitness in children, especially in those with a low HGS. Components of prenatal, prepubertal and pubertal growth have long-term consequences for midlife HGS [38]. Early interventions that facilitate building muscle mass could also prevent morbidity and mortality in later life [39‐41].

Unfortunately, measuring HGS is not commonly practiced in pediatric population, despite the low cost and portability of the device, thus, our study suggests to implement the measure HGS.

We should mention some limitations of this study. First, our findings should be interpreted with caution, due to the place where they originated. However, this investigation was carried out on representative samples of the Italians children potentially increasing knowledge on this issue from a geographical perspective. In addition, we did not performed the nutrient intake assessment or used any questionnaires evaluating performance status in this sample and a medical examination was not carried out. We sought to facilitates the participation of the children. However, parents were requested to inform the researchers of any clinical condition affecting participants or, alternatively, to exclude their son from the study. It was possible that this fact affected data. However, a total of 63 children excluded themselves from the study, probably on the basis of our exclusion criteria. Nevertheless data on the physical activity are lacking, in this study we excluded those practicing competitive sport but included those practicing a recreational sport, since it could be assuming a relevant influence on HGS only in the first [42]. Of course, other unmeasured confounders could exist explaining the observed associations. Finally, our study is limited by its small size. However, the statistical analysis is adequate. Our results were not purely random as established by a previous investigation [20, 21] and were confirmed by multiple statistical analyses.