BMX racing: rear wheel biomechanics

In BMX racing, the Olympic event since 2008, maximum force must be applied to the pedals in all cycling. Researchers at the Pprime Institute have been asked to help athletes and their coaches better objectify their gestures and improve their performance.

At the highest level, athletes determine more time and movement than ever before. In this pursuit of accuracy and accuracy, science is increasingly being sought, especially for major events such as the 2024 Olympic Games in Paris. At the crossroads of engineering, mechanics and medicine, biomechanics is one of the most popular areas. Improved performance. “” Biomechanics is the application of mechanics to biological systems, especially the human body.Mathieu Domalin, a faculty researcher at the Pprime Institute (P’), explains. The two axes are traditionally distinguished. The first one is mine, about the study of movement, but other scientists are interested in the resistance of biological materials and tissues. Working with my colleagues, I’m developing a more macroscopic approach. For example, analyze the force exerted on muscles and joints... »»

Mathieu Domalain’s work was initially involved in ergonomics, physiotherapy and rehabilitation to support physician diagnosis and selection of the optimal treatment solution for each patient. These studies were conducted specifically at the University of Poitiers Hospital. Later, Matthew Domarin gradually turned to paleontology and helped to understand fossil morphology and the link between physical activity and human evolution. He also turned to a very high level of sport, and above all.

BMX rider waiting behind the start gate. The backpack has a system for recording the force applied to the pedals (analysis conducted in Saint Quentin en Eveline in the training and competition course of French team pilots in 2019).

“” In this context, biomechanics helps to objectiveize performanceSays Matthew Domaran. Coaches and their athletes benefit from their eyes and experience. Thanks to the figures, we contribute to the gesture techniques used so that athletes and their staff can make informed decisions. It provides tools to better understand the functioning of the human body in performance situations, based on an analysis of speed, joint angle, and coordination between segments. This is how they get a tenth of a second that makes the difference between 1st and 2nd place... »»

The Pprime Institute, where Mathieu Domalin works, was asked by the French Cycling Federation to provide coaches with scientific support. The Research Center has been collaborating with various organizations for 30 years in the study of sports gestures, especially with Poatier’s expertise and the National Sports Experts and Performance Institute (Insep) of Sports Performance (Creps) and the Resource Center. Creps is, among other things, responsible for training sports federation executives and helping young people at the top level. Creps de Poitiers also has the peculiarity of having its own R & D unit. “” Creps brings expertise closer to sports and trainers with concrete solutions and regular supportSays Matthew Domaran.As researchers, we do not have the same time scale, but this brings true complementarity to our expertise... »»

Sportsmen are equipped with retroreflective markers (gray balls) found by optoelectronic camera systems. It is placed in the main joint and reflects the radiation captured by the camera. This allows you to track those trajectories and perform kinematic analysis of the gestures performed.

Châtellerault is also about 20 minutes from Pprime, a regional center for innovation and technology transfer (Critt) specializing in sports and leisure, whose director is a former PhD student at Pprime. These three structures are put together through Image Analysis and the Sports Performance Center (Caips) to provide a particularly attractive ecosystem to support the Sports Federation’s performance projects. The request from the French Cycling Federation is about BMX racing. At the Olympics, BMX actually exists in two different ways. BMX racing is a race between eight athletes on terrain dotted with bumps and banked turns, while BMX Freestyle consists of chaining figures on the ground and in the air. Pprime researchers are studying the effectiveness of each cyclist’s gesture technique and the impact of hardware characteristics such as bicycle frame shape and crank length.

For this, they use the classic tools of biomechanics. In particular, this includes an optoelectronic system consisting of approximately 15 high frequency cameras. These capture motion thanks to reflective markers stuck at the level of anatomical landmarks. From the coordinates of the recorded points, the algorithm analyzes the dynamics of the motion. Another part of the work is about force analysis. “”BMX uses special sensors to better understand the interaction between the foot and the pedals.Mathieu Domalin explains.BMX experts are cyclists who apply maximum force to the pedals. The event lasts only about 40 seconds, during which it makes sprints, jumps, and especially sharp turns. This device makes it possible to measure not only the amplitude of these forces, but also their direction, ensuring the efficiency of pedaling operation... The sensor used was designed by Sensix, a former PhD student at Pprime, but the institute is also exploring the development of its own measuring device.

Reconstruction of movement from modeling multibody dynamic systems. The green arrow indicates the force exerted on the pedal.

As the 2024 Olympics in Paris approach, missions are doubling. Therefore, at the end of 2020, six projects were allocated € 8 million by a call for a very high performance sports research project led by the Ministry of Higher Education, Research and Innovation and the Ministry of Youth Sports. Mathieu Domalin is one of them, and Perf Analytics is headed by Lionel Revet of Inria Grenoble. “”PerfAnalytics aims to provide coaches with daily video and other measurement tools.Says Matthew Domaran.Sure, we have all the equipment we need in the lab, but it’s not suitable for in-flight measurements.. Much research is being done. For example, the improved ergocycle is inevitably different from a competitive bike. In BMX racing, the gap is even wider because you can’t simulate a cyclist jumping or passing over a bump, which is an essential element of the field.

Therefore, the purpose is to be able to perform measurements and analyzes in training and competition venues. This includes developing alternatives to reflective markers used in wireless transmission, sensor miniaturization, and motion capture. Artificial intelligence tools, including deep learning, are also designed to analyze data directly from traditional camcorders. A serious enhancement to the weapons available to coaches and players.