Abstract :
[en] Introduction
Isokinetic and functional jump tests are frequently performed for assessing physical qualities of soccer players during preseason(1, 3). The main purpose of this investigation was to explore, in a high-level soccer players population, the relationships between isokinetic strength and functional jump performances.
Methods
Thirty-eight male soccer players from a belgian first division professional soccer club were included (mean age: 24±6 years; height: 183±8 cm; weight: 77±7 kg). The test battery was composed of: an isokinetic knee assessment (Cybex Humac Norm® dynamometer (CSMI, Stoughton, USA)) in concentric (CON) mode (60 and 240°.s-1) for quadriceps and hamstrings, and in eccentric (ECC) mode for the hamstrings only (30°.s-1)(2); one-leg hop tests for distance (single hop (SH), triple hop (TH) and triple crossover hop (TCH)); one-leg vertical jump tests (counter movement jump (CMJ) and drop jump (DJ) on force plates (Kistler®, Kistler Group, Switzerland)).
Results
No correlations were found between all the isokinetic (absolute or relative performances) and the jump parameters (r<0.40). Players with a low bodyweight normalized (BWN) quadriceps (Q) strength (<2.71N.m.kg-1, first quartile) showed significant reduced jump performances (maximal height of CMJ, absolute and relative peak vertical ground reaction forces of DJ, all hop test performances; p<0.05) compared to the players with high BWN Q strength (>3.14N.m.kg-1, third quartile). Hamstrings-to-quadriceps ratios were not correlated with hop or vertical jump performances (r<0.40). In the past injured group (n=17), greater bilateral differences between uninjured and past injured lower limbs were found with isokinetics (Q CON 60 (mean bilateral difference (MBD): 10.3%; p<0.01), Q CON 240°.s-1 (MBD: 9.9%; p<0.05), H ECC 30°.s-1 (MBD: 16.1%; p<0.001)) than with functional tests (MBD: 2 to 9%; p>0.05) excepted for TCH (MBD: 8%; p=0.01). Concerning the group without past injury, no statistical differences were found between dominant and non dominant sides for all the isokinetic or functional variables (p>0.05).
Conclusions
According to our results, it might be appropriate to associate vertical jump tests or hop tests with an isokinetic assessment during a preseason soccer players screening. Furthermore, given that bilateral differences between past injured and uninjured limb were mostly highlighted by the isokinetic test than by functional tests, the isokinetic test seems to be an essential tool for preseason assessment. Finally, as a low BWN quadriceps peak torque at 60°.s-1 is related to a weak jump performance, strength and conditioning professionals should take into consideration this parameter in the player’s assessment.
References
(1) Bogdanis GC, Kalapotharakos VI. Knee Extension Strength and Hamstrings-to-Quadriceps Imbalances in Elite Soccer Players. Int J Sports Med. 2016; 37(2):119–24.
(2) Croisier J-L, Ganteaume S, Binet J, Genty M, Ferret J-M. Strength imbalances and prevention of hamstring injury in professional soccer players: a prospective study. Am J Sports Med. 2008; 36(8):1469–75.
(3) Menzel H-J, Chagas MH, Szmuchrowski LA, Araujo SRS, de Andrade AGP, de Jesus-Moraleida FR. Analysis of lower limb asymmetries by isokinetic and vertical jump tests in soccer players. J Strength Cond Res. 2013; 27(5):1370–7.
