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Research - Sport

Jean-Michel Prima - 23/05/2016

Optimizing Tennis Serve

Tennis et numérique © C.Martin

Biomechanical analysis of high-level athletes can help not only to enhance their performance but also to prevent injuries. In Rennes, Brittany, France, members of the MimeTIC research team have started a partnership with the French Tennis Federation with aim of improving service technique among young hopefuls.

200 km/h. 124 mph. That's the speed a first ball of a serve must reach if a tennis pro is to make the podium. So better hit hard. “It can be very damaging a gesture indeed, all the more so that it is reiterated hundreds of thousands of times in a player's career, ” says Caroline Martin , a teacher at the Faculty of Sport Sciences of Rennes 2 University, in Brittany, France. Once ranked among French top ten junior players, she is also a coach. In 2013, she defended a Ph.D. thesis on the biomechanical analysis of the serve within MimeTIC research team in the M2S (Movement Sport and Health) research lab. In the wake of this work, in september 2015, she was instrumental in striking up a partnership with the French Tennis Federation.

The gist? “Helping players to develop the most performing as well as the less damaging technique. So there are clearly two aspects in this research. ” Scientist will carry out the biomechanical analysis of forty-some helpfuls aged 13 thru 20. “The work has already begun. Small groups of players come to our laboratory for a 3D motion capture session with Vicon infra-red cameras. We have a high frequency of up to 300 images per second. It allows for better motion decomposition and offers a precision of capture that standard video would not deliver. ”  This undertaking is performed in the brand new scientific gymnasium of the M2S lab located in Rennes École Nationale Supérieure (ENS), on the Ker Lann campus.

Why thus placing the focus on young players? “Because they are the ones whose technique is the most easily perfectible. There is no weight of habits yet. Conversely, a 25-year-old player has been serving with a certain technique for years already. Even if they are offered our diagnostic, they will find it way more difficult to modify their practice. Further, if young players get injured during initial training, their career risk stagnating. ” Most current injuries regard the back, the abdominal muscles and the shoulder. The scientific challenge is to “identify the risk factors that lead to these injuries.

The analysis will first extract “kinematic parameters that are linked to postures, speeds or angles. For instance: what is the maximal knee flexion angle when the player flexes legs during the serve, what is the speed of the racket head, what is the speed of the shoulder.We can correlate all these elements to the speed of the ball, which is a factor in the performance. ” Secondly come dynamic indicators. “Those are more related to the constraints on the joints. One can estimate the constraints of compression, distraction, torsion. Our methods enable us to compute these values and correlate them to the risk of injury.
Having been collecting metrics for several years, the researchers have built a database that proves instructive. “During my Ph.D., I compared players who had not been injured to players who had. We were able to show that the latter were those for whom constraints were higher. We established the link between the constraints brought to bear on the shoulder and the tendonitis.

Quantifying Training

Following from there, the researchers “try to understand where are the mistakes in the technique that will result into an excessive joint loading. ”  In the context of the partnership with the Federation, players will be analyzed at least once a year. “At scientific level, this will enable us to quantify the evolution of their technique, but also to establish what are the mandatory routes leading to optimum performance according to age and gender. Granted there are parameters that a 13-year-old player cannot be expected to master as someone in full physical maturity. But others parameters are already within reach at that early age. We will draw a roadmap of these gestures that a player is supposed to master, say, at 15 or 17. That's the road to expertise and to the transformation of the technique.
Incidentally, another problem surfaces: “How to ensure that scientific findings translate into practical application? If we show a player what their ideal gesture should be, if we tell them that the elbow angle should be, say, 45° rather than 50°, it doesn't mean that they will be able to perform this gesture. Therefore, coaches have a crucial role to play in this regard.

Deadlocks

This research also prompts new questions, including some emanating from the courts. “Coaches often ask how energy is being transferred throughout the body from the legs to the racket. It's a very interesting topic, but a complex issue from the scientific point of view. In the fields of sports and biomechanics, everybody bandies about this concept of energy transfer, but nobody has quantified it yet. To apprehend this phenomenon, one must come up with a method for computing indicators. ” Technological limitations are also to be reckoned with. “We use electromyographic sensors (EMG) to measure muscle activation. Placed on the surface of a biceps, for instance, these electrodes will tell us at what moment of the serve the muscle strongly contracts. Correlating this information to performance or injuries is worthwhile. However, there are deep muscle inside which, obviously, we can't place electrodes.
Once those problems taken of, would it be conceivable to build a model?  “Ideally, that's what should be done, Martin concurs. We would thus be able to simulate the optimum technique for a given player, taking into account their height, muscle mass and morphological profile. Still, we are not there yet...

Keywords: Carole Martin Immermove Tennis Numérique INRIA Rennes - Bretagne Atlantique MimeTIC M2S Sport

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