Enhanced bone mass and physical fitness in prepubescent footballers

Abstract

Not much is known about the osteogenic effects of sport activities before puberty. We tested the hypothesis that football (soccer) participation is associated with enhanced bone mineral content (BMC) and areal density (BMD) in prepubertal boys. One hundred four healthy white boys (9.3 ± 0.2 years, Tanner stages I–II) participated in this study: 53 footballers and 51 controls. The footballers devoted at least 3 h per week to participation in football, while the controls did not perform in any kind of regular physical activity other than that programmed during the compulsory physical education courses. Bone variables were measured by dual-energy X-ray absorptiometry. The maximal leg extension isometric force in the squat position with knees bent at 90° and the peak force, mean power, and height jumped during vertical jumps were assed with a force plate. Additionally, 30-m running speed, 300-m run (anaerobic capacity), and 20-m shuttle-run tests (maximal aerobic power) were also performed. Compared to the controls, the footballers attained better results in the physical fitness test and had lower body mass (−10%, P < 0.05) due to a reduced percentage of body fat (4% less, P < 0.05). The footballers exhibit enhanced trochanteric BMC (+17%, P < 0.001). Likewise, femoral and lumbar spine BMD were also greater in the football players (P ≤ 0.05). The femoral and lumbar BMC, and to a lower extent the BMD, were correlated with the lower limb muscle mass and the whole body lean mass. Interestingly, among all physical fitness variables, the maximal isometric force showed the highest correlation with total and regional BMC and BMD. Multiple regression analysis indicated that the 30-m running speed test, combined with the height and body mass, has predictive value for whole-body BMC (r = 0.92, P < 0.001) and BMD (r = 0.69, P < 0.001) in prepubescent boys. In summary, football participation is associated with improved physical fitness, reduced fat mass, increased lean body and BMC masses, and enhanced femoral and lumbar spine BMD in prepubertal boys. The combination of anthropometric and fitness variables may be useful to detect children with potentially reduced bone mass.

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.