Bone resistance can be enhanced as a response to high impact loads associated from regular sport training, and by high levels of tension in specific bone areas as a result of muscular contractions. There is, in general, a lack of information on the relationship between muscle strength and bone mass in youth populations. PURPOSE: To analyse the relationship between isokinetic peak torque (PT) of the quadriceps (Q) and harmstrings (H) muscles and bone mineral density and content (BMD, BMC) of the lower limb of youth male soccer players and age-matched controls non involved in sport (11-15 years). METHODS: 58 young males were divided in 2 groups according: soccer players (SP; n=39) and nonathletic controls (C; n=19). The former were regularly involved in soccer for at least 3 years (3-5 sessions a week, more than 300 minutes a week), while the latter participated only in the compulsory physical education classes at school (2 weekly sessions of 45-90 minutes each) and did not participate in any kind of regular or organized sport activity for at least 3 years. Isokinetic dynamometry at an angular velocity of 90°.s-1 was used to determine the maximum voluntary concentric torque of the Q and H muscles of the dominant and non-dominant limb. BMC and BMD were quantified with dual energy X-ray absorptiometry. Habitual physical activity was monitored with accelerometers during waking hours for 8 consecutive days. Maturity status was assessed by stage of pubic hair according the Tanner method. Statistical procedures included ANCOVA and multiple regression models. RESULTS: SP showed higher mean PT of the Q and H and higher BMC and BMD of lower limb than C (154.7±27.7 vs 108.7±23.5 Nm; 78.0±21.3 vs 45.6±11.5 Nm; 470.5±85.4 vs 288.8±66.0 g; 1.29±0.12 vs 0.96±0.10 g/cm2; respectively). No significant differences were found between dominant and non-dominant limb strength, BMC and BMD in both groups (p>0.05). After adjusting for maturity status, leg extension PT and soccer practice were positively associated with lower limb BMC [b= 2.54, p<0.001; b= 63.24, p=0.001, respectively; R2 =84.5%] and BMD [b= 0.03, p<0.001; b= 0.18, p<0.001, respectively; R2 =81.4%]. CONCLUSIONS: Muscle strength of knee extensors of boys is associated with lower limb BMD and BMC. Regular training for soccer contributes to the enhancement of lower limb BMD and BMC.