Dynamic Characterization of Human Tendons

Abstract

Human tendons were tested in uniaxial tension with the use of specially designed grips and the local measurement of tendon cross-sectional area. The resulting stress-strain relationship was non-linear in form, with the modulus of elasticity initially increasing to a constant value which decreased as the tendon failed. The ultimate tensile strength (UTS) for the extensor digitorum longus and extensor hallucis longus tendons were 99.9 ± 12.2 MPa and 87.1 ± 125 MPa, respectively. Dynamic characterization of those tendon specimens was achieved by the method of forced oscillations using dedicated software on a hydraulic testing machine. Specimens were subjected to cyclic tension-tension loads at frequencies in the physiological range of 1–4 Hz. The sta*** load was set at values corresponding to prescribed levels between 10 and 80 per cent of the calculated UTS. Results suggest that both the dynamic modulus and the storage modulus were non-linearly proportional to the mean static stress level reaching a peak value at 60 per cent UTS, whereas the loss modulus was independent of the mean static stress. All three dynamic parameters were generally independent of frequency. The trends in the dynamic parameters were explained in terms of the loading/unloading response of tendons, as well as the structural organization of their collagen fibres.