Viscoelasticity of the individual spine

Three subjects held barbells of 10.5 and 20.5 kg on the shoulders for 45 min. At regular intervals both stature and trunk height were measured using a stadiometer. Experiments were performed in the morning and afternoon and each condition was repeated three times. The three repeated measurements were averaged, yielding eight creep curves per subject. These curves were fitted with the equation describing a Kelvin unit. The ratio of the elastic modulus and the coefficient of viscosity was used to characterize the viscoelastic response. All inter-subject differences were significant. No differences were found between the creep rates concerning stature and trunk height, 10.5 and 20.5 kg load, and morning and afternoon. Characterization of the viscoelastic properties of the individual spine based on these relatively simple measurements appears to be possible.