In an effort to determine more accurately the physical characteristics of human tendon, stress-strain and tensile strength studies were performed on tendons removed from amputated lower limbs. The tendons of M. extensor digitorum longus, M. extensor digitorum brevis, M. extensor hallucis longus, M. flexor digitorum longus and M. flexor hallucis longus were used in the studies. Tensile strength of the extensor tendons averaged 13,392 psi while that of the flexor tendons was less, with an average of 10,944 psi. These results indicate that, of the tendons tested, the extensors are about 20 per cent stronger than the flexors.

The stress-strain data were analyzed by a computerized statistical method utilizing a multiple-regression analysis employing as many as 8 variables. All stress-strain curves shown were derived by this method. The difference in stiffness previously reported to exist between embalmed flexor and extensor tendons was not manifest in the present study. However, in the range from 0 to 3.0 per cent strain, thought by many to be the normal physiologic range, extensors and flexor tendons were seen to react differently to stress. The flexors initially exhibited greater strain per unit stress and gradually became stiffer, the stress-strain curves exhibiting an upward concavity. The extensors were initially stiffer, gradually responding with more strain per unit stress, and the stress-strain curve was slightly concave downward. The stress-strain curves of unembalmed flexor and extensor tendons as calculated in the present study are reminiscent of the curves previously reported for embalmed extensor tendons.