A novel design for an instrumented stairway

Kinetics during stair ambulation is currently studied via either the use of sensing elements embedded in the steps of the stairway or simple rigid blocks of different height positioned on top of existing force platforms, typically embedded in a walkway for gait analysis. Neither of these approaches is truly satisfactory for gait analysis laboratories. The first one is expensive and requires setting up a dedicated space. The second approach is limited by the number of platforms utilized in the laboratory for evaluating level walking. This communication proposes a novel design, referred to as "interlaced stairway", that allows one to measure ground reaction force and position of the center of pressure (CoP) for four foot contacts during stair ambulation using only two force platforms embedded in a walkway. Accuracy and precision of the CoP estimates and natural frequency of the stairway structure were derived from experimental data. Test results indicate that the interlaced stairway structure does not appreciably reduce the quality of the measures gathered by the existing force platforms. Specifically, the estimated CoP coordinates show good agreement with the horizontal coordinates of the geometric center of the calibration object utilized to assess accuracy and precision of the CoP estimates (max difference < 6 mm). The natural frequency of the stairway structure is lower than the one for the unloaded force platform but higher than the frequency components of interest in stair ambulation analysis.