The wheelchair tennis events open this Friday, August 30 on the clay courts of Roland-Garros. After Novak Djokovic and Zheng Qinweng, who will leave with the gold medals? France has a real chance of a medal with Stéphane Houdet, double gold medalist in doubles in Rio and Tokyo. We will also follow in the women’s event Pauline Déroulède and Ksénia Chasteau, recent winner of Roland-Garros in the juniors.
The rules are similar to tennis with the notable exception that players are allowed to hit the ball after two bounces. The sport, like other wheelchair disciplines, relies on a classification system that ensures the inclusion of people with different levels of ability. In wheelchair tennis, there are two main categories: the Openreserved for players with lower limb injuries, and the category Quadintended for those with lower and upper limb injuries.
The improvement in performance at the recent Paralympic Games is largely due to the evolution of equipment. Stéphane Houdet is a perfect example: in addition to his playing skills in tennis, he is constantly looking for innovations to improve his chair. Athletes are moving faster and faster and now often hit after the first bounce to maintain the speed of the ball, which makes them more threatening. Athletes do not use everyday chairs, but sports chairs specially designed to meet the requirements of the different disciplines. They are recognizable by their lightness, their large inclined wheels, and their small rear wheels called “anti-tips”, ensuring stability, speed and maneuverability, thus offering athletes optimal mobility on the court.
Optimizing the athlete’s mobility
Performance in wheelchair tennis is based on two major fundamental areas. First, as with able-bodied players, physical and mental abilities, as well as technical mastery, including variation and precision in ball strikes, are crucial and require rigorous training. However, the particularity of this sport lies in the mobility of the athlete with his wheelchair, which remains essential due to the speed of the game and the extent of the court to be covered.
This is precisely the aspect that I am examining in my thesis. In order to support athletes towards the highest level of performance, the French Tennis Federation has decided to support the development of this research project. The main objective is to help the staff guide athletes in the choice and adjustment of their chair according to the different playing surfaces (clay, hard, grass), with the aim of personalized optimization of the settings. A multitude of parameters can be adjusted according to the athlete’s morphology and their positioning in the chair: the depth and width of the seat, the height of the backrest, the camber (the angle of the wheels relative to the vertical), the size of the wheels, the advance of the seat, and many others.
Wheelchair tennis is an intermittent aerobic activity, which means that it combines low- or moderate-intensity endurance phases, marked by continuous and regular movements to reposition oneself and anticipate opponents’ shots, with more intense phases involving rapid movements, such as sprints or sudden changes of direction, to retrieve a ball at the net or on the opposite side of the court.
Clay, a demanding surface
To optimize player mobility and reduce the effort required to move, it is essential to consider the interaction between tires and casters with the playing surface. This contact creates rolling resistance, a physical phenomenon that opposes rolling, which leads to a loss of energy and can reduce the athlete’s ability to move. This resistance forces players to exert more effort, particularly in the upper limbs, thus increasing the risk of injury.
On the occasion of the Paralympic Games, held on the legendary clay court of Roland Garros, the question of the optimal configuration of wheels and castors to minimize rolling resistance was examined in collaboration with the Federation. A previous study showed in particular that, for the same configuration, rolling resistance on clay is 1.5 times higher than that on hard courts. The most restrictive surface remains grass, which has a resistance 5 times higher than that on hard courts. However, until now, no study had specifically looked at the best combination of wheels and castors to adopt.
To answer this question, we tested different combinations using “deceleration carts”. These carts, specially designed for the experiment, allowed us to analyze the effect of several parameters of the large wheels, such as camber, pressure and tire type, as well as those of the casters, taking into account their diameter, hardness, material and profile.
The experiment consisted of manually pushing the cart along a straight line, then letting it slow down naturally until it came to a complete stop. Using inertial measurement units (lightweight, compact sensors), we measured the linear speed of the cart and then calculated the deceleration rate. By multiplying this rate by the mass of the system, we were able to determine the rolling resistance force. A lower force indicated a more efficient configuration, with less resistance.
The results showed that the type of tire and its pressure are essential elements in choosing the best configuration. The characteristics of the castors also proved important and should not be underestimated. For example, for the rear wheels, the tire pressure has a considerable impact on friction. With the same configuration (mass, camber, identical tires), an optimal pressure reduces the resistance by 1.42 times compared to a less suitable pressure. Similarly, using the “best” castor tested, friction is reduced by 1.8 times compared to the “worst” castor. These tests were essential in guiding athletes in the optimal choice of their tires and castors, in order to minimize rolling resistance on clay.
Analyze player movements
At the same time, to optimize locomotor performance, it is essential, in a sporting context, to be able to analyze the characteristics of the movements made during a match.
While technologies such as GPS and video analysis are commonly used in able-bodied athletes, their application in wheelchair sports is more complex and challenging. Wheelchair tennis is mainly played indoors, where GPS is not functional, and the court dimensions are relatively small (~12 x 5.5 m for a half-court). This requires a level of detail and precision that GPS cannot currently provide. As for video analysis, it requires a team of analysts to manually record each movement, a very laborious and time-consuming task.
To overcome these limitations, the installation of inertial units on the athlete’s chair, combined with the development of a locomotor task detection algorithm, made it possible to recognize six types of movements in wheelchair tennis: the static phase, forward straight-line propulsion, backward walking, rotation on the spot, tight rotation, wide rotation.
The sensors collect data such as linear speed, rotational speed, and radius of gyration (which represents the distance between the center of mass of the chair and the point around which it rotates). These signals are then analyzed, and their combination allows to identify the six locomotor tasks mentioned above. As illustrated in the photo, each locomotor task is color-coded, and parameters such as speed, acceleration, and distance are extracted to characterize the movements, thus providing a simple and effective tool for the Federation staff to track movements throughout a match.
Finally, this project is part of a long-term approach, aimed at optimizing wheelchair settings in an individualized manner. Although some knowledge is already available, there is currently no standardized method for testing the impact of different settings on propulsion biomechanics. To fill this gap, CERAH (Centre for Studies and Research on Disabled People’s Equipment) is developing a multi-adjustment ergometer, designed like a wheelchair, which will make it possible to assess the impact of the main adjustments on wheelchair tennis movements and on joint constraints, particularly at the shoulder level. This innovation could mark a significant step forward in the customization of equipment to maximize performance and minimize the risk of injury.
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