Original articleEnhanced bone mass and physical fitness in prepubescent footballers
Introduction
Acquiring a high bone mass during childhood and adolescence is a key determinant of adult skeletal health [1]. Nowadays, however, children spend less time practicing sports or physical activities, while they devote more time to activities such as watching television and playing video games [2]. This sedentary life style predisposes to obesity and may attenuate the accrual of bone mass leading to a lower peak bone mass.
In contrast, physical activity has an important osteogenic effect [3], [4], [5], [6], [7]. Football (soccer) is possibly the sport most widely practiced in the world by children. The exercise intensity of football ranges from walking to sprinting. During a football match, an adult male covers a mean distance close to 11 km [8] at an average intensity similar to that observed during marathon running (70–80% of the maximal oxygen uptake) [8]. The effects of running, the most important physical activity in football, on bone remain controversial because lower vertebral bone mineral content (BMC) and density (BMD) have been found in adult male long-distance runners compared with sedentary controls [9]. In prepubescent female runners, however, there is no effect of exercise on BMC or BMD until the start of puberty, when a greater femoral and lumbar BMD has been reported in runners compared to sedentary control girls [4]. Nevertheless, football involves several sprints, which evoke high additional mechanical stress on lower limb bones due to higher ground reaction forces during sprinting [10]. Additionally, a high number of actions which are characteristic of this sport are likely to be ostogenic. For instance, the forces generated while rapidly changing direction, stopping, and landing, as well as during jumping and kicking, may confer excellent osteogenic properties to football at least in weight-bearing bone sites [3], [4], [5], [6], [7].
In fact, we have recently observed that adult amateur football players have increased BMC and BMD at the lumbar spine, hip, and lower limbs compared with age-, height-, and weight-matched sedentary controls of the same Caucasian population [5]. However, it remains to be determined how clinically relevant skeletal regions, such as the lumbar spine or the femoral neck, respond to the mechanical stimuli evoked by football participation in prepubescent children. This information will improve our knowledge about the effects of physical activity on the growing skeleton, which is otherwise very limited [4], [11], and is required to propose scientifically grounded guidelines for sport participation at a prepubescent age.
The main aim of this study was, therefore, to test the hypothesis that, in prepubescent boys, playing football for at least 3 h per week has additional osteogenic benefits to that obtained from the compulsory physical activities included in the physical education program of primary schools. A secondary aim was to determine which physical fitness related variables are the best predictors of BMC and BMD in prepubescent boys.
Section snippets
Subjects
A representative sample of the Gran Canaria child population was obtained by multiage stratified sampling, using as a reference the database of the ISTAC (Instituto Canario de Estadística). In total 433 healthy children and adolescents, between 7 and 20 years old, were recruited from different schools and football clubs of Gran Canaria. However, only the 104 prepubescent boys (Tanner < 2) were included in the present investigation. Both parents and children were informed about the aims and
Physical characteristics and physical fitness
The subject's age, anthropometrics, calcium intake, and physical fitness data are summarized in Table 1. When comparing football and control groups, both were similar in height and age, but the footballers had 10% (P = 0.05) lower body mass than the control group. Also, the percentage of body fat (%BF) was lower in the football group (20.6 ± 1.1% versus 24.4 ± 1.6%, P < 0.05; Table 1).
The footballers attained better results in aerobic maximal power, anaerobic capacity, running speed, and height
Discussion
The principal finding of the present study is that prepubescent footballers show higher lumbar spine and femoral BMD than their non physically active age-, weight-, and height-matched control subjects. Moreover, as expected, prepubescent footballers have less fat mass and better physical fitness than their sedentary counterparts.
The beneficial effect of football practice on bone development is well-documented in adults [5], [6]. Increases in whole-body, hip, and lumbar spine bone mass in female
Acknowledgements
Special thanks are given to Juan José González Henríquez from the Department of Mathematics at the University of Las Palmas de Gran Canaria for his excellent support in the performance of the statistical analysis. The work of Nicola Leadbeater in reviewing the English style and grammar is greatly appreciated. We also acknowledge José Navarro de Tuero and Jorge Cortadellas Izquierdo for their excellent technical assistance. This study was supported by grants from the Ministerio de Educatión,
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