Force treadmill for measuring vertical and horizontal ground reaction forces

We constructed a force treadmill to measure the vertical, horizontal and lateral components of the ground-reaction forces (F-z, F-y, F-x, respectively) and the ground-reaction force moments (M-z, M-y, M-x), respectively exerted by walking and running humans. The chassis of a custom-built, lightweight (90 kg), mechanically stiff treadmill was supported along its length by a large commercial force platform. The natural frequencies of vibration were >178 Hz for F-z and >87 Hz for F-y, i.e., well above the signal content of these ground-reaction forces. Mechanical tests and comparisons with data obtained from a force platform runway indicated that the force treadmill recorded F-z, F-y, M-x and M-y ground-reaction forces and moments accurately. Although the lowest natural frequency of vibration was 88 Hz for F-x, the signal-to-noise ratios for F-x and M-z were unacceptable. This device greatly decreases the time and laboratory space required for locomotion experiments and clinical evaluations. The modular design allows for independent use of both treadmill and force platform.