An instrumented footbar for evaluating external forces in Pilates

The intensity of Pilates exercises is almost exclusively based on experience. Therefore, knowing the precise amount of effort that is exerted during exercises could be useful for professionals conducting exercise assessments and for future research using inverse dynamics (ID) analyses. The reformer is an apparatus that contains a carriage on rails to which resistance is applied via springs attached to the carriage. Subjects apply force to a footbar to displace the carriage, but the magnitude and direction of this force are unknown and need to be quantified if the ID approach is to be used. This study aimed to develop and describe a device built with commercial load cells attached to the reformer's footbar, with the device capable of measuring the direction and magnitude of the force exerted on the reformer's footbar, and to compare the force found using the device with the force estimated using the springs' parameters. To illustrate the device's use, one volunteer performed footwork exercises at different speeds and with different foot support positions and loads. External force estimated by the springs' level of deformation was significantly different (P < .001) from the magnitude of force acquired using the device, showing that the estimation is imprecise.