Protocolos para la evaluación biomecánico-técnica y la prevención de lesiones musculo-esqueléticas, en deportistas de raqueta

Abstract

Despite the fact that there are numerous studies aimed at designing a test protocol for tennis players and other racket sports, from our point of view these protocols have some disadvantages: I) the tests included in them are often not completely specific (they do not simulate the real actions of the game); II) they focus mainly on aspects of physical condition and a comprehensive protocol must also include biomechanical/technical aspects and aspects related to the risk of musculoskeletal injury; III) they are based on expensive and difficult to use instruments, not affordable for coaches and athletes or for health clinics that have a low budget or do not have time to learn how to use them.. Therefore, the objective of this thesis is to design, implement and validate comprehensive protocols oriented to racket sports that evaluates different variables related to performance, sports technique, and prevention of musculoskeletal injuries. On the other hand, databases of tests used repeatedly in the literature will be generated. This could serve as a reference for future studies. Some of these tests are: • Physical condition block: specific speed and agility tests, medicine ball throwing test, manual grip strength test, CMJ and RCMJ jumps, repeated sprint test. • Biomechanical/technical analysis block: tennis hitting test (technical) in which variables of precision and power are measured, tennis hitting test (specific endurance), in which global fatigue is related to the accuracy and power of the strokes. • Block aimed at preventing musculoskeletal injuries. Analysis of the body composition by means of bioimpedance, anthropometric analysis and evaluation of the running mechanics with force platform and pressure sensors. In this thesis, evaluation tools and protocols are designed for racquet sports, affordable for coaches, athletes and health clinics with a limited budget. A series of results derived from the application of the tests in different samples of racket athletes are also shown. The most interesting results are mentioned below, dividing them by blocks: The most interesting results in the physical condition block are: • The results of young paddle tennis players in a series of physical condition tests are shown, which could be used as a reference for future studies. The results were worse than those described in literature for tennis players of the same age and of a similar competitive level both in speed and jumping ability as well as hand grip strength. There is a moderate correlation between global power (measured with the lateral medicine ball throw) and hitting power / precision. Specifically, it was positively correlated with faster forehand speed (r = 0.52; p <0.025) and with the accuracy of the backhand (r = 0.49; p <0.025 with the % of good shots). In order to improve hitting performance in players with a limited training time (as is the case of amateur players) it is advisable to spend more time on technical preparation than on physical preparation. • This thesis shows a methodology for timing the shuttle run sprint more accurate than a human timekeeper. The systematic error of measurement was of approximately 0.04 seconds (in previous studies it is estimated that human error is between 0.20 and 0.30 seconds). The methodology shown only requires the use of a smartphone and low-cost apps. In the biomechanical / technical analysis block the most interesting results are: • The error in tennis is distributed in the form of an elongated confidence ellipse in the direction of the baseline. This could be explained by the theory of the optimal launch window, which, making an analogy with hitting, indicates that there is an optimal hitting moment where the highest precision will be achieved. In the case of paddle tennis, a greater error is also observed in the longitudinal direction than in the lateral direction. All of this suggests that more time should be spent training the accuracy of the depth of strokes. The comparison between the forehand stroke and the backhand stroke showed that with the forehand the players reach greater speed of the ball (~ 107.2 vs. ~ 97.3 m/s; p <0.001), had a lower longitudinal distance from the centre of the ellipse (~ 123.3 vs. ~ 164.0 cm; p = 0.024) and a smaller area (~ 34.4 vs. ~ 40.3 m2; p = 0.045). The hit that showed the greatest error was the backhand with the wall. The forehand performed from the baseline and the forehand volley showed the best accuracy values. Also, a hitting test associated with an Excel spreadsheet is proposed to study in detail the accuracy of tennis groundstrokes (magnitude and form of the error). • In this thesis a Microsoft Excel tool is shown to evaluate the 3D kinematics of hitting. This sheet is easy to use and does not require advanced knowledge of biomechanics or programming. Some of the variables it provides are the trajectory of the racket and derived variables (e.g., the height of the ball impact or the angle of the racket trajectory and the horizontal), the speed and acceleration of the racket, the speed of the ball before and after impact and temporal variables (such as the moment at which the maximum racket's vertical speed occurs). A variant of said 2D analysis template is also shown (it only requires one camera and the calibration methodology is simpler). • The gyroscopes of the IMUs are a valid tool to evaluate the angular kinematics of hitting, with small differences with respect to the motion capture systems based on 3D photogrammetry, which have traditionally been considered as the reference method. The correlations and concordance statistics were strong (ranged from 0.951 to 0.993). The magnitude of the differences varied between 4.4 and 35.4 degrees/sec (in percentage relative to the maximums, the error was less than 5%). Based on data from previous work on tennis players, we can say that the error of the gyroscopes is low enough to detect differences both in studies that make a comparison between subjects and in repeated measures studies. Therefore, they can be considered as an alternative to evaluate hits in a field situation. • The gyroscopes of the IMUs allow predicting the speed of hitting the forehand, backhand and serve. The partial Pearson r correlations were above 0.8 in some cases (in x-axis of the trunk sensor's and in the y axis and z axis of the forearm sensor). The multiple linear regression model improved the correlation values. In addition, the proposed method allows an analysis of the relative implication of the most relevant segments in the stroke. In the future, laboratory studies should be carried out that relate anatomical movements (for example, the horizontal abduction movement of the shoulder) with the angular velocity of the sensors placed at different points on the body (for example, angular velocity of the sensor of the arm on its medial-lateral axis). • The forehand and the backhand showed greater motor variability than the serve, which could indicate that they are more complex hits from the coordinative point of view. The highest values of variance were found on the forehand in the forearm sensor on its x axis and on its z axis, and in the head sensor on its z axis (they were of 22.7%, 21.5% and 25.4%). More studies are needed on the anatomical significance of these movements and on the relevance to performance / skill learning of the greater variability in them. The most relevant results in the musculoskeletal health block are: • Paddle tennis, like other racket sports, is an asymmetrical sport at the level of the upper limbs. There were greater asymmetries of lean mass than a control group of skiers (7.2 ± 5% vs. 1.4 ± 3.2%; p <0.001 for the total sample) both in players with a negative state of maturity (5.7 ± 3, 2% vs. 1.5 ± 3.8%; p <0.001) and in those with a positive state of maturity (8.3 ± 5.8% vs. 1.3 ± 2.4%; p <0.001). In the case of manual grip strength, there were also significant differences with big effect sizes (greater than one): it was of 22.1 ± 13.2% in the case of paddle tennis players (in the sub-12 group it was of 19.3 ± 14.8%) and of 2.6 ± 13.3% in skiers (in the sub-12 group it was of 1.8 ± 16.9%). These data show that the development of such asymmetries occurs even before the age of peak growth in height. For this reason, it is suggested that, from the beginning of sports practice, paddle tennis should be complemented with other activities of a symmetrical nature. A low-cost methodology is presented to analyse body posture in 3D, based on a portable calibration instrument. In addition, it allows to measure the error committed in the real unit of measurement, something that we believe is essential (and unusual) in this type of study. This methodology is based on easy-to-use Excel templates that could be utilised by trainers and scientists in the area. The error when compared to a high precision 3D photogrammetric system was small (approximately 2 mm for translations and between 1–2 degrees for angles). • As in running and walking, in the game of tennis a series of mechanisms for attenuating the impact peaks are put into play in the spine that prevent the impact peaks on the head from being too high. Although there was no clear attenuation mechanism between the lower part of the spine and the upper part, there was a clear attenuation between the upper part of the spine and the head (the magnitude of the peaks was of ~ 25 m/s2 and of ~ 20 m/s2 respectively; p <0.05; with attenuation percentages above 15% in almost all players). Future works should analyse the biomechanics of these attenuation mechanisms.