Background The functional asymmetry (FA) of the soccer player lower limb is often analyzed to reduce the risk of injury. In football have been described power asymmetries (Samadi et al., 2009; Bittencourt et al., 2008; Rahnama et al., 2005), differences in plantar pressure (Wong et al., 2007), asymmetries in vertical jump (Impellizzeri et al., 2007), differences in the ground reaction forces during the landing between dominant and non-dominant limb (Sannicandro, 2008). The FA, however, besides being a significant element of risk of injury, can affect the performance of the soccer player.
Objective The study aims to analyze the relationships between asymmetry of the strength of the lower limb and sprint in professional footballers.
Design Descriptive research (a correlation study which investigates the relationship between variables).
Setting Soccer Elite Division, at the end of off season conditioning.
Participants 25 soccer players (26.1 ± 2.9 year, 179.8 ± 3.6 cm, 77.9 ± 2.5 kg).
Assessment of risk factors The assessment of explosive strength was performed through monopodalic jump, in literature defined as hop test and sprint test on 10 m and 20 m through photocells (TTSport, San Marino).
Main outcome measurements FA was calculated between the two limbs as follows (jump dominant-limb – jump non-dominant limb)/jump dominant-limb * 100 (Yamamoto, 1993; Impellizzeri et al., 2007). This value was correlated with the results (sec) obtained in the 10 m sprint and 20 m sprint.
Results The analysis of the correlation between FA and sprint 10 m and 20 m sprint between FA and showed values equal respectively to r=0.702 (p<0.001) and r=0.215 (ns).
Conclusion The results would suggest that the FA in the lower limb explosive strength affects the performance of short sprints, but not those of the longer sprint. In the 20 m sprint, other factors, such as cyclic speed and intermuscular coordination, could be of greater importance.