INFLUENCE OF RACING POSITION ON CYCLING PATTERNS

INTRODUCTION: In endurance cycling, a major goal is to maximize the cycling speed sustainable for a given distance. A variety of internal and external factors can influence cycling speed. Among these, physiological and biomechanical factors influence power production (internal factors), and mechanical and environmental factors affect mainly the relationship between power output and cycling speed (external factors). One of the only variables cyclists can adjust during a race to manage performance is body position. Body position can act both as an external factor and as an internal factor. The effect of body position on the relationship between power output and cycling speed can be calculated with the experimentally measured drag area in different body positions (Jeukendrup & Martin, 2001). From this point of view, an upright posture is clearly detrimental. On the other hand, racing position in cycling could also act as an internal biomechanical factor influencing cycling patterns and power production. Some experimental studies have already shown that body position can significantly affect power output in endurance cycling (Jobson et al., 2008, unpublished work from our institute). The exact mechanisms underlying the increased power output with a more upright posture have not been analyzed in detail. Dorel et al. (2009) analyzed the influence of body position on the effective pedal force and on electromyographic patterns during cycling, but they did not measure the kinematics of the limbs nor the ineffective pedal force.The main goal of this study was to examine the effect of racing position on the pedal forces, the kinematics of the lower limbs, the muscular joint moments and the muscular joint powers. METHODS: Six well-trained male amateur cyclists (28 ± 3 years, 180.3 ± 3.1 cm, and 68.3 ± 7.1 kg) performed a cycling trial at 200 W with a cadence of 80 rpm in two racing positions: upright posture (UP) with hands on the top portion of the handlebars and arms fully extended and dropped posture (DP) with hands on the drops of the handlebars and arms fully extended (Fig. 1). The position and orientation of the pelvis and the segment lengths (thigh, shank, and foot) were measured statically (Fig. 1). Both pedals were equipped with a force measurement device that measured the parallel and normal component of the pedal force using strain gauges. Furthermore the pedal angle and the crank angle were measured using angular potentiometers. Hence the resultant pedal force can be subdivided into the tangential pedal force and the radial pedal force (Fig. 2). Joint-specific angles and angular velocities were then calculated using inverse kinematics. The measured and calculated forces and kinematics needed for the inverse dynamics were averaged over ten pedal revolutions. The minimal and maximal values of the variables over a complete pedaling revolution were analyzed. Joint-specific muscular moments and powers were then calculated using inverse dynamics and averaged over complete pedal revolutions (Pjoint) and over the regions with finished the exercise with a higher lower limb extension, and therefore a different muscular activation pattern could have occurred. Increasing the friction with the ground is recommended to avoid trunk slipping during this exercise at high speeds. In relation to the trunk flexion, there was no change in the strategy used to raise the trunk from the force plate (commonly: first a curl up of the upper trunk, followed by a hip flexion), since the ROM of the DF and DLF angles did not change (table 1). Nevertheless, a reduction in the amplitude of the UTH ROM was found, which may be due to a reduction in the downwards movement of the trunk and head at the end of each repetition with the intention of following the rhythm at the higher cadences. Surprisingly, the speed increase in the LRL reduced the pelvic ROM. This could be interpreted as a result of an increase in the trunk muscle coactivation, which in many cases could be a desired effect (Vera-Garcia et al., 2006 & 2007). But this should be taken cautiously because simultaneously there was a reduction in the hip ROM and an increase in the knee ROM (more flexion when it should be constantly extended). This is also interpreted as a modification of the exercise technique to reduce the radius of gyration and so the angular momentum, facilitating the objective of following the higher cadences. CONCLUSION: The results indicate that the exercise technique changes when the speed of movement increases. Most of these changes seem to be due to the subjects’ difficulty to keep up with the higher exercise cadences. Sport and exercise professionals should bear this in mind when using these exercises at high speeds, and continuously correct the athletes’ modifications of the technique.