• Yiannis Michailidis.
• Laboratory of Evaluation of Human Biological Performance, Department of Physical Education and Sports Science, Aristotle University of Thessaloniki, New Buildings of Laboratories, University Campus of Thermi, 57001 Thessaloniki, Greece.
• Medicina (Kaunas). 2023 Sep 29; 59 (10).

AbstractBackground and Objectives: Asymmetries between the lower limbs were evaluated by both researchers and practitioners as they seem to be related to the occurrence of injuries and the effect on performance. The purposes of this study were to (a) detect asymmetries of the lower limbs using a unilateral jump (single-leg countermovement jump (SLCMJ)) and 505 agility test, and (b) examine asymmetry effects on fitness (acceleration, speed, squat jump, Illinois agility test), in U16 youth male soccer players. Materials and Methods: Twenty U16 soccer players performed an SLCMJ and a 505 test to calculate the asymmetry index. They also performed the above fitness tests. The difference between the lower limbs was tested using the paired samples t-test (dominant vs. non-dominant). The correlations between the asymmetries of the lower extremities with the performance indicators were tested using the Pearson's correlation test. The level of significance was set at p < 0.05. Results: The lower limbs differed significantly in the SLCMJ and 505 tests (p < 0.05). The only correlation was between the asymmetry in SLCMJ and performance in SJ (r = -0.641, p = 0.002). Asymmetries did not affect performance on most fitness tests. Conclusions: The two asymmetry tests identified asymmetries in different limbs. This indicates the variability in asymmetries and the need for specialized tests depending on the kinematic chain. The asymmetries observed should be eliminated using individualized training programs so that athletes are protected from injuries and from the possible negative impact on performance. Also, the detection of asymmetries in developmental age offers a greater time period for their elimination before the athlete enters professional sports.

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