THOMPSON, A. M., A. D. G. BAXTER-JONES, R. L. MIRWALD, and D. A. BAILEY. Comparison of Physical Activity in Male and Female Children: Does Maturation Matter? Med. Sci. Sports Exerc., Vol. 35, No. 10, pp. 1684–1690, 2003.
Purpose: TTo investigate whether observed differences in physical activity levels in boys and girls are confounded by biological age differences particularly during the circumpubertal years.
Methods: T The physical activity questionnaire for children (PAQ-C) was administered biannually or triannually to 138 (70 boys; 68 girls) Canadian children for seven consecutive years from 1991 to 1997. Participants were 9–18 yr of age. Anthropometric measurements were taken biannually and age at peak height velocity (PHV) determined. Biological age was defined as years from PHV. The data were analyzed using t-tests and random effects models.
Results: TLevel of physical activity decreased with increasing chronological age in both sexes. When aligned on chronological age bands, boys had statistically significantly higher PAQ-C summary scores than girls from 10 through 16 yr of age (P < 0.05). However, when aligned on biological age, sex differences were not apparent, except at 3 yr before PHV. Random effects models of individual growth patterns confirmed these findings.
Conclusion: TPhysical activity decreased with increasing chronological age in boys and girls. There were no sex differences in the longitudinal pattern of physical activity when the confounding effects of biological age were controlled except at 3 yr before PHV.
It is commonly believed that boys are more physically active than girls. Results from several investigations using self-report measures of physical activity confirm this supposition (8,11,18,22,24,25,30). For example, in an investigation of 1540 boys and 1671 girls between the ages of 11 and 18 yr in Northern Ireland, boys reported significantly more minutes of physical activity at all chronological ages (24). Using a different self-report instrument, the Physical Activity Questionnaire for older Children (PAQ-C), Ernst and Pangrazi (8) found that among 4th, 5th, and 6th grade children, boys reported higher levels of physical activity than girls. In yet another study comparing children in the 4th, 5th, and 6th grade, boys reported being involved in significantly more physical activities and athletic training programs (22). A study investigating intensity of physical activity found that boys in the 4th and 6th grade reported more moderate and vigorous intensity physical activities than girls (11). In terms of actual hours, boys (8.8 ± 6.2 h·wk−1) reported they were significantly more physically active than girls (6.0 ± 5.7 h·wk−1) in a study of 120 children between the ages of 6.5 to 13 yr (18). Finally, in a longitudinal investigation of health, fitness, and lifestyle, it was reported that girls were less physically active than boys at each year of investigation from ages 13 to 17 yr (30). Clearly, the literature supports the contention that boys are more active than girls at all ages during the circumpubertal years when physical activity is measured using a variety of self-report tools.
One major point not considered or controlled in the studies reported above was the maturational difference between boys and girls of similar chronological age. It is well known that girls, on average, mature 2 yr before boys (20). It is also noted in the literature that physical activity decreases with age in boys and girls (11,14,24,29,30). It is possible then that the lower level of physical activity reported in girls, when compared with boys using chronological ages, could be attributed to an earlier age of maturation. An analysis of physical activity that considers maturational age would be able to discern whether the differences between boys and girls in regard to level of physical activity are affected by maturational age.
The most commonly used biological age parameter in longitudinal growth studies is peak height velocity (PHV) (5,13,26,27). Outcome measurements are considered in terms of time before and time after PHV (19). This morphological measurement of maturational age has been shown to be appropriate for use in longitudinal studies. Specifically, it is noninvasive, nonintrusive, and of particular relevance for the present study because it is not gender specific (19).
To be able to consider maturational age in a comparison of physical activity levels in boys and girls, it is necessary to have longitudinal data and the statistical methodology to manage the data (random effect models). Cross-sectional data merely provide a snapshot view of an individual’s level of physical activity. Longitudinal data provide a series of pictures over time and are necessary for the determination of maturational age. An advantage of longitudinal data is that individual variation in level of physical activity can be statistically handled. To examine group differences, a growth curve must be fitted to each individual’s repeated measurements and an average curve developed from the individual curves (9). There is wide variation among children in level of physical activity at any given age and in the change in activity level from one age to the next. As a result, it is essential that the modeling procedures and statistical analyses account for these differences in the most efficient way possible.
The purpose of the present investigation was to determine whether the interpretation of physical activity levels, as measured by self-report questionnaire, was confounded by maturational status in children before and during pubertal development.