Muscle strength and soccer practice as major determinants of bone mineral density in adolescents

Objectives: To analyse the relationship between isokinetic strength of the lower limb muscles and bone mineral density and content (BMD, BMC) of adolescent male soccer players and age-matched controls not involved in sport (12-15 years). Methods: A random sample of 151 young males was divided into soccer players (SG; n = 117) and control subjects (CG; n = 34). Peak torque of knee extensors (PTE) and flexors (PTF) was measured during isokinetic knee joint movement (90 degrees/s) of the dominant and non-dominant lower limbs. BMD and BMC of the whole-body, lumbar spine, dominant/non-dominant lower limb were determined by dual-energy X-ray absorptiometry. Physical activity was monitored with accelerometers during 5 days. Estimated maturity offset was used as an indicator of biological maturity status. Results: Whole-body BMD (1.03 +/- 0.01 vs. 0.98 +/- 0.01 g/cm(2), P = 0.003) and dominant (1.09 +/- 0.01 vs. 1.02 +/- 0.01 g/cm(2), P < 0.001) and non-dominant (1.09 +/- 0.01 vs. 1.01 +/- 0.01 g/cm(2), P < 0.001) lower limb BMD was greater in SG compared to CG. No significant differences were found for BMC. Compared to CG, SG performed better in the YY-IE2 test (780 +/- 40 vs. 625 +/- 31 m), exhibited higher PTE (dominant limb: 155.2 +/- 30.3 vs. 123.4 +/- 37.0 N m; non-dominant limb: 156.2 +/- 36.1 vs. 120.4 +/- 41.1 N m) and PTF muscles (dominant limb: 79.0 +/- 25.3 vs. 57.1 +/- 25.3 Nm; non-dominant limb: 73.3 +/- 20.7 vs. 57.0 +/- 24.2 N m). Moreover, the PTE, soccer participation and maturity status were positively associated with the BMD at all body sites (r(2) = 0.57-0.73, P < 0.05). Conclusions: Muscle strength of knee extensors is associated with BMD and BMC at all body sites. Muscle-skeletal structures respond positively to the weight-bearing and impact-loading imposed by soccer practice. Soccer seemed to be a multilateral balanced sport activity. (C) 2011 Societe francaise de rhumatologie. Published by Elsevier Masson SAS. All rights reserved.