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).

Professor 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, extensors, lateral 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

More detailed data

Of course, these conclusions remain individual and personal, and it would be very difficult to apply them to general advice for all tennis players. ʺEvery player is unique: they have their own characteristics and physical qualities, their own technique, their own strengths and weaknesses. It’s impossible to draw conclusions that are valid for all players, but we can nevertheless form a general outline to prevent unsuitable movementsʺ, Cédric Schwartz explains.

In this particular case, the analyses showed that the player in question tilted his pelvis (anteversion) more than other players. ʺWhile this problem can clearly be seen in a 2D video, the 3D images made it possible to quantify it. And it was possible to see it regardless of the player’s position in relation to the cameras, since the markers provided us with the information. This wouldn’t have been the case with a simple video. That’s the advantage of a 3D analysis. We saw that this pelvic tilt could be influenced by a deficit in leg drive combined with incomplete leg extension amplitudes. Thanks to an isokinetic analysis, among other things, we also observed that this wasn’t due to muscular weakness (hamstrings) but rather tension here”, François Tubez explains.

It is necessary to observe the whole chain to understand why these movements and faults cause pain. And to be able to provide advice on how to deal with the problem to prevent it from happening again. This analysis therefore led to recommendations for various specific exercises, such as abdominal core strengthening exercises. ʺThe results of the analysis were sent to the trainer who was then able to adapt the training sessions according to our observations. And during the following test, we observed an improvement in the movementʺ, he is glad to say.

Changing isn’t easy…

When learning a sport, and specific movements, we may tend to adopt bad habits which, nevertheless, enhance performance. ʺWhile it’s impossible to say what you should and shouldn’t do for each sport, we can see, as an athlete evolves in their particular sport, movements or positions that we know are harmful for their body. There are recurring injuries in every sport and it’s often possible to address them by making adaptations. The problem is that if the player considers that they should continue to play this way to remain at the top of their game, there’s a good chance that they won’t be receptive to our advice…ʺ. For instance, when amateurs see a player of the calibre of Rafael Nadal playing, and see him passing his arm over his head after a forehand, they may be tempted to imitate him. And yet, this movement isn’t necessarily adapted to their build, their morphology or their level of fitness. But because they’re convinced of the effectiveness of this champion’s movement, they won’t be motivated to stop doing it. ʺWith players who run a risk with some of their movements, we can offer a biomechanical analysis to observe the consequences of such a movement. But there’s no certainty that a correction will have a positive result in terms of prevention. Not to mention the opinion of the trainers who can’t always change the habits of their champion, especially if they’re playing in a tournament. Unfortunately, the international ranking system forces them to play a lot, which doesn’t leave much time to adapt to new habitsʺ, Cedric Schwartz continues.

Prevention in young players

Can we therefore use the analyses relating to injured athletes, and the conclusions drawn from these cases, to teach these youngsters more beneficial habits? Clearly, we can’t rule this out: ʺThis year, we observed children aged 8 to 11 who are members of the AFT, with the idea of specifically analysing their movements and raising awareness among their trainers about the need to maybe make changes on a biomechanical level. Because although they’re already part of the elite, they’re still young and still learning. Perhaps the bad habits haven’t already established themselves and their motor pattern is more ‘malleable’. We put them through a series of tests to study them individually and to compare, with a control group, the leg drive, the pelvic movement, the impact of the ball, etc.: the goal was also to observe the sequence of action of the movements of all parts of the body when serving. And to draw conclusions and send them to their trainer, who would then be able to give them precise and individualised exercises”, François Tubez concludes.

Finally, what is true for tennis can also be true for other sports. Through the training given to trainers by ADEPS, for instance. This organisation has indeed reviewed the training given to its managers, who now look at aspects linked to biomechanics, to provide them with the main principles and protocols to detect at-risk behaviours. This professionalisation, which exists in the majority of countries, but especially in the largest clubs, will certainly benefit the performance of our high level sportsmen and sportswomen.

(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