Assessing the reliability of inter-limb asymmetry in the 1RM back squat and its relationship with dynamic balance, muscle power, speed, and change of direction in pre-pubertal male soccer players

Purpose: Players who engage in these motor activities are more likely to develop strength imbalances, which have both clinical and practical ramifications. Bilateral strength tests have been used in soccer to measure lower limb power. The present investigation aimed to investigate the reliability of lower limb strength asymmetry and its association with dynamic balance, change of direction, jump, and sprint ability in pre-pubertal soccer players. Methods: Thirty-one pre-pubertal male soccer players participated in the study. All players were assessed for dynamic balance (CS-YBT), single leg hop test, 4 x 5-m change of direction test (15-m COD), 10, 20, and 30-m linear sprint times, back squat unilateral and bilateral maximal dynamic muscle strength (1RM), and lower limb strength asymmetry (%). Results: Absolute reliability was verified for all variables through a coefficient of variation (CV) < 10%, except for strength asymmetry (CV: 37.30%). The intra-class correlation coefficient (all > 0.709) confirmed the relative reliability of all parameters. In addition, there was a moderate positive correlation between strength asymmetry strength and bilateral 1RM (r = 0.415, p = 0.020). The study confirmed the absolute reliability of all tests with two exceptions: strength asymmetry (which was calculated with absolute reliable variables) and right leg single hop (only by a small margin of 0.33%). Conclusions: Strength activity and training should be provided to pre-pubertal soccer players with less balance and coordination to reduce lower limb strength asymmetry. Furthermore, all strength tests can be considered for youth soccer players for talent detection.