ʺServingʺ tennis players

All tennis players will tell you that a good serve is an extremely important asset in a match. And yet, this movement, which is practiced over and over again, is by no means harmless and can cause pain and even injury to the upper and lower limbs, as well as the trunk. To analyse this movement, from the point of view of performance and the prevention of tears, researchers from the Laboratory of Human Motion Analysis (LAMH) at the University of Liège studied high level players. A summary of their conclusions was published in the Journal of Sports Science and Medicine (1).

Tennis ServiceProfessor Jean-Louis Croisier, from the Department of Sciences of Motricity at ULg’s faculty of medicine, and Professor Bénédicte Forthomme, a lecturer in the same department, asked François Tubez to focus on a study of the serve in tennis: ʺSince I play tennis myself, have a degree in physical education and a masters in physiotherapy and rehabilitation, and have done courses at the AFT (Association francophone de Tennis) and ADEPS, etc., they decided to entrust this project to me.ʺ Professor Croisier put together a team comprised of different members, involving the Laboratory of Human Motion Analysis (LAMH), of course, and the intervention of Doctor Cédric Schwartz, among others, as well as various departments at ULg (Department of Sciences of Motricity, Department of Aerospace and Mechanical Engineering – LTAS, Department ArGEnCo), and Liège CHU.

Identifying the pain

ʺOur study focused on the case of a 22-year-old high level international tennis player who felt a sharp pain while serving. He told us he experienced this pain when the trunk was in extension and he was starting the flexion. We concluded that as he was executing this stroke, the abdominal muscles were going from eccentric contraction to concentric contraction. Clinical examinations, such as magnetic resonance imaging, revealed a tear in the rectus abdominus muscle. The location of this tear is indeed well known as a well-defined site for injuries during the serveʺ, François Tubez continues. Once this diagnosis was made, the player underwent physiotherapy as well as an isometric evaluation of the trunk muscle, i.e. the flexors, extensorslateral flexors and rotators. This evaluation showed a weakness of the right lateral flexors in comparison with the left, as well as too much stress on the flexors compared with the extensors.
After the overall evaluation and once the treatment had finished, it was then necessary to find out why this tear occurred by specifically analysing the player’s serve. After all, the aim isn’t to let the player keep making the same problem movement, but to correct it so that there is no reoccurrence of the pain or the injury! And this is where this study starts to be really interesting.

3D analysis

The injured player was compared to five other players of the same level with no injuries. ʺOf course, you could say that a study involving six people is a bit thin on the ground, but our objective was to analyse a specific case. Furthermore, we had to take into account our player’s level of play. He was in the top 50 ATP ranking, so it wasn’t easy to find Belgian players with a comparable level who were willing to undergo our tests for the comparisonʺ, says Cédric Schwartz, co-author of this article.

In order to be able to make an in depth and reliable analysis of the movement, the researchers had to be able to observe the movement as well as possible in conditions as close as possible to reality. ʺIn general, these analyses are based on video images of the player executing the movement. For the study, we used a 3D image in addition to this 2D image. To achieve this, we first reproduced a tennis court in the laboratory, and placed a 1-m² target zone in the corner of the service box. The player and his racket were equipped with 28 markers and the data from these markers was sent to cameras located around the court. This allowed us to observe the movement of the pelvis, arms, legs, etc., as well as the racket. A radar calculated the speed of the ball, while the 3D markers measured the speed of the racket on impact with the ball. The point is that this speed is only influenced by the force exerted and the technique used by the player, not by the equipment usedʺ, Cédric Schwartz continues. Couldn’t this test have been carried out on an outdoor court? ʺWe could have done but in order to examine the player’s stroke in depth, we placed him on a force platform, which is only available in a laboratory. It allows us to assess the leg drive. This complete analysis integrating the effort of the lower limbs allowed us to draw a fair number of interesting conclusions.ʺ

(1) F. Tubez et al., Biomechanical Analysis of Abdominal Injury in Tennis Serves. A Case Report, Journal of Sports Science and Medicine, 2015. http://hdl.handle.net/2268/180795

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