Background Functional asymmetries of the lower limbs(FA) have been recognised as a potential source of injury risk of in soccer players;moreover a difference in strength performance between the lower limbs exceeding 15% is considered an injury risk factor. Preventative strategies should be integrated into young football player training regimes⇓⇓.

Objective To assess the presence of FA in the lower limbs and evaluate whether the percentage of subjects presenting asymmetries exceeding 15% increases with age.

Design Cross-sectional studies.

Setting Youth sports.

Participants 427 young soccer players: 9.1±0.1 years, 36.3±6.5 kg, 137.9±7.1cm (n=227) and 11.2±0.1 yrs, 43.8±9.7 kg, 148.9±9.1 cm (n=200).

Risk factor assessment Monopodalic jump;all three versions were employed: Single (SI), Triple (TR) and Side hop(SE) is considered a valid indicator of FA in the lower limbs.

Main outcome measurements Strength in each of the lower limbs was assessed by means of the SI, TR and SE test; the percentage of FA between the lower limbs was calculated using the formula proposed by Yamamoto, 1993: (jump dominant-limb-jump non-dominant limb)/jump dominant-limb*100.

Results The percentage valuesare summarised in tables 1 and 2.

Conclusions The highest percentage of subjects presenting asymmetries was detected in the 11yr-olds. Comparing the results for the two age groups revealed a statistically significant difference for the SideHop test.