Validazione di una nuova metodica per la valutazione della potenza esplosiva dei muscoli estensori degli arti inferiori:differenza tra un test di salto verticale (Jump Test) ed un test di spinta alla pressa orizzontale (Push Test)

Muscular explosive power of the lower extremities is a critical performance factor in many types of sports. The most widely used test to measure explosive power is the jump test, which is considered the gold standard owing to its validity and reproducibility. However, the jump test involves complex movement that creates problems of repeatability and spinal overload. In contrast, the leg press test appears easier to perform and less problematic as regards repeatability and overloading. Use of the push test has been reported elsewhere, but to our knowledge no published data are available that correlate the jump and the push tests. To fill this gap, the aim of our study was to verify correlations between the two tests in order to validate the push test as a method for measuring explosive power of human leg extensor muscles and to identify the optimal load to be applied with this method for obtaining maximum mechanical power. The study population comprised a group of 16 physically active males randomly assigned to two different testing sessions: one with the push test and the other with the jump test. In both tests muscular power without countermovement was measured. The push test was performed on a horizontal press (Technogym Italia) with the subject in a sitting position and the knees and hips bent to 90°. The subject was asked to push as hard as possible against the carriage using both legs while the carriage was free to move backward along two tracks. A series of tests were performed using progressively heavier loads (100-120-140-160-180-200% of body weight). The test was repeated 3 times with each load. The jump test was performed with the subject starting in a semisquat position with the knees bent to 90°. Tests were carried out using natural weight (body weight) and progressively increased loads (10-20-30-40-50% of body weight) on a force platform. The test was performed in triplicate for each load. For both the jump and push tests, parameters were measured using an encoder (ErgoPace Italia) fixed to the floor (jump test) or to the press stand (push test). Measurement of translational load shifting was processed using dedicated software in order to obtain data on strength, speed and power. For each test method and subject, the power output values for each load were then interpolated to determine peak power output and amount of load expressed as per cent of body weight to which they corresponded. Data on strength, speed and power obtained for the load corresponding to the power peak were analyzed to compare the two tests. The results showed a statistically significant correlation between the two test methods as regarded strength and power (r=0.723; P<0.001 and r=0.486; P<0.05, respectively), while speed emerged as an r coefficient of positive correlation but not statistically significant (r=0.297; P=0.264). The measurements obtained with the two test methods and compared using t-tests differed significantly for all parameters: strength resulted higher on the push test, while power and speed were higher on the jump test. Peak power was obtained with an overload of 78% more than body weight on the push test and an overload of 7% more than body weight on the jump test. The study results demonstrate the validity of the push test for measuring explosive muscular power of leg extensors. Therefore, this test can be used for comparing performance between subjects and long-term monitoring of training. The method also offers several advantages: ease of use, less involvement of coordination ability, better standardization of the method and less spinal overload. Furthermore, the different power outputs of the subject and the different loads with which peak power is achieved indicate that the two apparently similar methods used for the same purposes differ in motor action. While on the one hand the greater loads used in the push test are partly related to the presence of cams that facilitate application of strength in the initial phase of movement, the higher output values obtained in the jump test (greater power), related to the interaction of accessory muscle groups, especially the erector muscles of the spine and the buttocks, suggest greater specificity of the push test for estimating only the capability of muscular explosive power of the leg extensors, specifically of the extensors of the knee (quadriceps). Hence, the push test appears better indicted for evaluating this performance factor for longitudinal and/or transversal control. Moreover, these difference suggest the need for future studies to compare biomechanical characteristics of the two exercises, with evaluation of gesture cinematics, joint dynamics, electromyographic activity, and different muscle lengths. This would help to better define which muscular mechanics are specifically involved in the two different movements.