Effect Of Exercise Volume On Bone Mineral Accrual In Adolescents Of Different Sport Modalities: 9 Months Of Follow Up

Sport practice is related to the improvement of bone health during human growth and also in adulthood. On the other hand, when targeting bone mass gain, it is not clear in the scientific literature the most effective sport modality on it mainly because sports performed in hypogravity (such as swimming) offer limited physical load on bone architecture. This longitudinal study was (conducted during 9 months between 2013 and 2014) composed of 75 adolescents of both sexes and aged between 12 and 16 years old, being: Control group (n=17), basketball (n=14), Soccer (n=18), Swimming (n=26). It were adopted as inclusion criteria: (i) chronological age between 11 and 17 years-old, (ii) previous authorization of the coach and parents to make part of the study, (iii) at least 6 months of previous practice of this sport modality (active group) or absence of any organized sport practice in the last three months, (iv) no medication use that could affect bone metabolism and (v) signed written consent form. Swimmers and soccer players, participate in competitions of national level while basketball players are engaged in championships of regional level. The analyzed outcomes refer to bone mineral density (MBD) [g/cm2]) and content (MBC) [g]) and fat free mass assessed using a dual-energy x-ray absorptiometry scanner (DEXA) in whole body. Somatic maturation was calculated using the peak of height velocity (PHV). Data about training routines (number of sessions per week and time spent per day) were provided by own coach and thus the weekly hours trained (minutes/week [min/wk]).Statistical analysis was composed of analysis of variance (Tukey's post-hoc test when necessary), analysis of covariance (Bonferroni's post-hoc test when necessary) and Pearson correlation. Measures of effect size were provided by Eta-squared (ES-r). All analyses were procedures performed in the software BioStat (v.5.0). After 9 months, the follow up values were significantly higher for soccer (3.8%), basketball (7.1%), swimmers (4.1%) and control group (3.7%). Sports groups had significantly higher values of BMD than control group in both moments of the cohort. Moreover, the above mentioned characteristics are observed in basketball practice, which would help to explain highest BMD gain (7.7% [95%CI: 5.6% to 9.8%]) in this group . The volume of exercise training was negatively related to bone mineral gain in swimmers -0.461 (-0.721 to -0.090) and soccer players -0.591 (-0.829 to -0.171), but not among basketball players 0.237 (-0.336 to +0.682). The practice of basketball has been associated with greatest bone mineral gains among adolescents. Moreover, high volumes of training seem harmful to bone formation during adolescence.

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