EXPERIMENTAL DEVICE FOR THE ANALYSIS OF THE CYCLER'S MOVEMENT

Abstract

INTRODUCTION This study deals with the characterization of the cycler's movement in its kinematic and dynamic aspects. The article presents the instrumentation of the cycle to characterize the differences between the clipless fixed and the clipless float pedals. METHODS A bicycle used in cycling sport competition and a home trainer constituted the experimental devices. The bicycle is fixed by its front fork and this device allows to simulate the seated position of a cyclist on the road. On the one hand, the system SAGA3 equipped with 4 CCD 50 Hz cameras allows the acquisition of kinematic variables. Cameras are placed according to the frontal and sagittal plane. The 2 cameras placed in the frontal plane allow the idenfication of known positions of markers on the lateral and medial femoral epicondyle and the lateral and medial malleolus. These 2 cameras contributed to increase the accuracy of the determination of articulate centers (Fig l).The accuracy is of 1.9% for distances and 1.82 for angles. On the other hand, a mini platform is used to acquire pedal loads (Fig 2). Its measurement range was 200 daN for Fz, 50 daN for Fx and Fy, 6 daN*m for Mz and 5 daN*m for Mx and My. The theorical accuracy is 1 % of the measurement range for the different components. To locate this force plate in the global reference system Ro(xo,yo,zo), a tripod was used and fixed under the pedal (Fig 1). In addition, a goniometer was used to determine the position of the crank arm at each moment. Experimental data were collected from the right leg of 1 male subject during seated cycling at 90 rpm and 200 W at a sampling rate of 50 Hz for 30 s. Prior data collection, subjects cycled at least 15 min at 85 rpm and a reduced power level of about 120 W to familiarize themselves with each pedals design. The data were averaged over 40 cycles. RESULTS AND CONCLUSION From a qualitative point of view, it is often said that in cycling the lateral movement of the clipless float pedals reduces the effective transmission of force from the shoe to the pedal. This torque is a function of the crank angle, of the forces Fx, Fz as stated in the Ro (xo,yo,zo) reference system. The two curves (Fig 3) are quite similar, which means that there is no effective loss of mechanical torque transmission from the shoe to the pedal when the floating pedal systems are used. This fact emphasizes Wheeler 's results (1995). In addition, for the clipless float pedals, the applied Mz moment at the pedal is weaker. This result is an indicator for the reduction of the axial moment realized at the knee (Ruby, 1992). This article describes the instrumentation to measure with optoelectronics systems and force platforms the cycler's movement. The experimental device was test with 1 male subject. With this subject, clipless float pedals reduce the applied Mz moment at the pedal without compromising power transmitted to the bike.