QUALITATIVE BIOMECHANICAL ANALYSIS OF THE "START" ELEMENT IN SPORT MOTOCROSS

Abstract

The purpose of this research is to analyze the fundamentals of kinematic structures in the starting element of motocross (Dirt Bike). To analyze the dynamic structures of movements, such as starting acceleration, linear velocity, criteria for the optimality of starting acceleration as the main factor for successful ranking in the competition. To determine the influence of the Center of Gravity of the pilot, on the successful control of the kinematic structures of the element of starting, to achieve a rational launching technique. We used the cinematic method (cyclogram analysis) to make a biomechanical analysis of the kinematic parameters of the "start" element in motocross. We shot photographic material, which is necessary for the analytical determination of the General Center of Gravity of the racer and the sports device (motorcycle). We determined the trajectory of the CG movement and the phases of the "start" element in the accelerating linear motion. The subject of research is the change in the kinematic parameters of the movements when performing a "start" in motocross. Participants in the research are six motocross racers, height 178.7±7.47 cm, weight 79.17±9.36 kg, age 32.17±8.84 y. (M±SD), BMI of 24.7 kg/m2 . We used a Go Pro HERO11 Black Cinematic 5.3K60 + 2.7K240 camera to capture the stills. Graphic processing was done with PAINT 3D program, Windows 10. For the statistical analysis of the data, we used GraphPad Prism version 3.0 software. In motocross, the simplified technical inventory leads to greater mobility and precise control of the machine in the specifics of the race track. That is why we hope to clarify some kinesiological regularities transferred to the „pilot-motorcycle“ system. Accurate and precise description of the movement and definition of its main task. The competitor's position is seated, semi-seated or semi-standing depending on the acceleration phases at the start. The palms are in a grip on the handlebars. The feet are placed on the foot pegs. The torso is bent forward. The movement is translational and follows the relief of the race track. We have identified five main phases of starting in motocross: 1) body positioning phase; 2) phase of the acceleration; 3) phase of the maximum acceleration; 4) phase of the maximum speed; 5) phase of occupying position for a corridor. For the successful performance of the competitor, an important point in the start is to avoid rolling, the loss traction and begin to slide, rear drive wheel in the starting position. The optimal range of linear acceleration at which the rear wheel will not lose traction was determined, namely from a = 2.77 m/s2 to 12.96 m/s2. We also determined the rear wheel load of 166.62 kg when accelerating from a standstill. This shows that the overload is about 76 kg more than the pressure that the rear wheel takes at rest. The load data of front wheel load show values of 38.78 kg on launch acceleration, which is a reduction in ground reaction force of around 50 kg. After evaluating the kinematics of the motocross riding posture, we found that the rider's upright posture gave the deceptive impression of lowering the overall center of gravity, when in fact it was the exact opposite. In fact, the rider's semi-upright position increases the height of the Center of Gravity and gives more precise control over the handling of the dynamic rider-motorcycle system.