CMJ 2.1 : functional test during post injury period in football player

Introduction Several methods have been widely used to assess bilateral asymmetry of the lower limbs (i.e.: Isokinetic Test, Star Excursion Balance Test, LESS Test, etc…), but they require very expensive equipment and/or do not reproduce the functionality of movements. Furthermore, these methods in some cases can be difficult to be performed. In this paper, we propose an easier method we named Counter-Movement Jump 2.1 (CMJ2.1) characterized by low cost of the equipment and by specificity of movements. The aim of this study were: 1) to evaluate the reliability of CMJ2.1; 2) if it could permit to define the level of the players, and 3) to determine functional deficits in injured players. We hypothesized that using the CMJ2.1, it could be possible to evaluate the ability to handle the eccentric strength and the leg impact on the ground. In particular, it could be possible to compare the healthy leg with the injured one. Methods Forty-nine football players (age: 21.07.0 yrs; height: 178.16.0 cm; weight: 73.65.3 kg) were recruited from local football teams and split into two groups: Healthy (HE; n=38) and Non-Healthy (NHE; n=11). The chosen participants who had been seriously injured during the previous year at the knee or at the ankle bringing about their inactivity for more than 30 days were considered NHE. Both groups were tested on traditional Counter Movement Jump landing on their two feet (CMJ). After that, the NHE group was tested on CMJ2.1 landing on the Non-Injured Leg (CMJ2.1NIL) firstly and on the Injured Leg (CMJ2.1IL) afterwards. Conversely, the HE was tested on countermovement jumps landing on the Right foot firstly and on the Left one afterwards (CMJ2.1R and CMJ2.1L, respectively). The height (cm) of each jump was calculated from the fly time measured by Optojump Next (Microgate, Bolzano, Italy). The strength asymmetry between legs was computed as [(stronger leg-weaker leg)/stronger leg]*100 (1). Anything ranging from -15% to 15% (25th and 75th percentile, respectively) was considered normal (1). The Intraclass Correlation Coefficients (ICC) were calculated to assess the reliability of CMJ2.1. In accordance to Shapiro-Wilks’ normality tests, parametric and non-parametric paired and unpaired t-tests were performed using Aabel (versione 3.0.3; Gigawiz Ltd. Co, Tulsa, OK, USA). A p-value lower than 0.05 was considered statistically significant. Results The CMJ2.1 ended up being actually reliable (ICC: CMJ2.1L=0.94 (0.91-0.97); CMJ2.1R=0.92 (0.86-0.95); CMJ2.1NIL=0.94 (0.91-0.97); CMJ2.1IL=0.92 (0.87-0.95)). No statistical difference (P>0.05) within bipodal CMJ was found between HE (37.15.0 cm) and NHE (36.55.6 cm). In HE, statistical differences were found between CMJ and CMJ2.1R (P<0.001), and between CMJ and CMJ2.1L (P<0.001). However, no statistical difference was found between CMJ2.1R (33.04.9 cm) and CMJ2.1L (32.84.7 cm). In this group of players the range of normal bilateral asymmetry ranged from -6.6% to 6.2%. In NHE, statistical differences were found between CMJlib and CMJ2.1NIL (P<0.001), between CMJlib and CMJ2.1IL (P<0.001) and between CMJ2.1NIL (31.14.4 cm) and CMJ2.1IL (28.24.5 cm) (P<0.001). In this group of players the range of normal bilateral asymmetry ranged from -18.5% to 15.9%. Conclusions The football players performed lower vertical jumps when they must landing on one leg during CMJ. It could be due to the intervention of central nervous system mechanisms that inhibited the maximal production of force. The statistical difference and the wide range of normal bilateral asymmetry between the CMJ2.1NHL and CMJ2.1HL confirm the efficiency of this method to detect the functional deficits in injured athletes. These results could be due to the fact that when the subjects must landing on one leg, in particular on injured one, unconsciously they reach a lower height to reduce the impact on the ground (2). In addition, the functional test CMJ2.1 is strongly reliable and efficient as it lets you discriminate the injured leg from the non-injured one. CMJ2.1 is easy to execute, it does not need expensive equipment and takes into account the functionality of movements. For these reasons, this method may turn out to be useful for coaches, strength and conditioning coaches and sports scientists to evaluate injured players level of rehabilitation. References 1. Impellizzeri FM, Rampinini E, Maffiuletti N, Marcora SM. A vertical jump force test for assessing bilateral strength asymmetry in athletes. Med Sci Sports Exerc 2007; 39, 2044-2050 2. Withrow TJ, Huston LJ, Wojtys EM, Ashton-Miller JA. The relationship between quadriceps muscle force, knee flexion, and anterior cruciate ligament strain in an in vitro simulated jump landing. Am J Sports Med 2006; 34: 269-274