Main findings
weight gain, overweight, adiposity
HOLIDAYS, HOLIDAY, ADIPOSITY
The focus of this study was to compare rates of change in children’s fitness and fatness between in-school and summer holiday periods, and to explore whether differences in rates of change in these outcomes were moderated by sex, SES, pubertal status, or weight status. During the holiday period, there was a significant increase in the rate of change of percentage body fat and a significant increase in the rate of decline of aerobic fitness, indicating differential increases in fatness and decreases in fitness in the holiday period. However, there were no differences in rates of change for BMI z-score, waist-to-height ratio, or standing broad jump. Some differences in rates of change in fitness and fatness were moderated by socio-demographic characteristics. In general, children who were overweight and from lower-SES families exhibited relatively faster increases in fatness and declines in fitness in the holidays compared to the in-school period.The study’s finding of summer holiday weight gain is generally consistent with previous studies [Few previous studies have examined whether summer holiday weight gain and fitness losses differ according to sociodemographic and anthropometric characteristics [Similar to Moreno et al. [Interestingly, patterns for summertime changes in fatness and fitness were not consistent for the various markers. Generally speaking, results were significant when fatness was considered based on %BF (and mostly consistent based on zBMI), but not when considered based on waist:height. It is likely that %BF measured by bioimpedance is a more sensitive measure of adiposity than zBMI and waist:height. Furthermore, it is possible that changes in body shape associated with puberty may have contributed to the lack of significant findings for the waist:height variable.Similarly, clear fitness losses were apparent in V̇OIt is interesting to consider that the significant increases in percentage body fat and decreases in aerobic fitness may even be directly related. Given that the 20mSRT is performed under gravity where children carry their entire body mass, a holiday-related increase in BMI should reduce 20mSRT performance. Fat mass per se does not affect aerobic fitness but increased fat mass could reduce 20mSRT performance and our estimate of V̇O