Measurement of transmissibility for the human spine during walking and running.

A method for measuring the transmissibility of the human spinal column to vertical vibrations using light-weight, skin-mounted accelerometers is described. The accelerometers were conveniently attached to the skin at the S2 and T2 levels of the spine using adhesive tape. The acceleration time records were analysed using a discrete Fourier transform to calculate the amplitude for each frequency component up to 40 Hz. Transmissibility was estimated as the ratio of the output over the input for each frequency component. The analysis included a compensation for both skin movement and differences in the inclination of the spine from the vertical at the accelerometer mounting sites. The healthy spine was observed to attenuate frequency components above 20 Hz, whereas in ankylosing spondylitis the spine behaved as a rigid strut.