FORCE TREADMILL FOR MEASURING VERTICAL AND HORIZONTAL GROUND REACTIONFORCES

We constructed a force treadmill to measure the vertical, horizontal a nd lateral components of the ground-reaction forces (F-z, F-y, F-x, re spectively) and the ground-reaction force moments (M-z, M-y, M-x), res pectively exerted by walking and running humans. The chassis of a cust om-built, lightweight (90 kg), mechanically stiff treadmill was suppor ted 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. Mech anical 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 decrease s the time and laboratory space required for locomotion experiments an d clinical evaluations. The modular design allows for independent use of both treadmill and force platform.