Connolly DR ¹, Bosio A¹, Riggio M¹ , Carlomagno¹ D, Rampinini E ^{1 ,2}

1, Human Performance Laboratory, MAPEI Sport Research Center, Castellanza, Varese, ITALY;2, Department of Sport, Nutrition and Health Sciences, Faculty of Exercise and Sports Sciences, Università degli Studi di Milano, Milan, ITALY

Bilateral strength asymmetry has been identified as a risk factor for musculoskeletal injuries. Measurement of bilateral strength asymmetry may therefore be implemented to identify athletes at an increased risk of incurring lower-limb injuries during training and competition. The aim of the present study was to monitor longitudinal changes in bilateral strength asymmetry by assessing soccer players performing vertical jumps. Data was collected from top professional (TP, n=14), professional (P, n=11) and young professional (YP, n=11) soccer players prior to pre-season (PRE), at the beginning of the league season (START), as well as at in-season testing (MID). Players performed eight countermovement jumps during a vertical jump force test (VJFT). The countermovement jump was performed with the test leg on a force platform (QuattroJump, kistler, Switzerland) with a sampling rate of 500Hz, and the contralateral leg on a wooden platform leveled with the surface of the force platform. Four jumps per leg were performed in a randomly selected order. The average of the four vertical peak forces (N) measured for each leg was used to calculate bilateral strength asymmetry. A significant time per group interaction was noted when comparing the 3 testing sessions performed by the TP, P and YP teams (P= 0.019). Post Hoc analysis revealed that bilateral asymmetry in TP decreased significantly (P<0.05) from PRE (9.0±7.2) to both START (5.2±5.6) and MID (4.5±3.6) points respectively. In contrast, bilateral asymmetry values remained stable across time for both the P and YP players (P>0.05). Overall, no significant differences were observed when comparing the 3 groups of soccer players. TP is the only group that reported a variation in bilateral strength asymmetry, suggesting that the type and quality of training being performed potentially influenced the outcome. However, on the whole these results indicate that undertaking soccer specific training alone will not positively influence bilateral asymmetry. The difference observed in TP could have been influenced by the fact that the TP group had a non-significant, but slightly higher percentage of bilateral asymmetry in PRE than both P (6.3±5.0) and YP (5.3±3.3) players. Further studies with larger sample sizes should investigate changes in bilateral strength asymmetry across an entire season and also examine the type of training being conducted more closely in order to determine its impact on lower-limb symmetry.

The 3rd World Conference on Science and Soccer in Ghent, Belgium: 14-16 May 2012