RESUMO
A strain gauge instrumented clipless force-plataform pedal, similar to those used in cornpetition by cyclists and triathietes, was designed and constructed. The system is capable of measuring two forces components over the 360 degrees circular amplitude. The geometry of the pedal was comprised of four beams in balance. Two full Wheatstone bridges were used, one for normal forces and one for tangential forces. Eight strain gauges were glued on the beams in a way to respond with 2000 micro strain when a load of 1800 N in the normal direction and 800 N in the tangential direction were applied. The calibration of the system was performed separately for each force component. In both cases the load-deformation relation was found to be linear and the compliance between the two forces was less than 5. Torques applied on the pedal bad no influence on tangential forces. Three trials were conducted and the normal and tangential forces were obtained. It was seen that the techniques adopted by a professional cyclist, a professional triathlete and a non-athlete differed considerably. The system was shown to be useful in mechanical efficiency studies as well as a source of feedback for cycling teaching or training.