On the independence of time and strain effects in the stress relaxation ofligaments and tendons

The hypothesis of variables separation, namely the time and the strain sepa ration in the relaxation function, is widely used in soft tissue biomechani cs. Although this hypothesis is central to several biomechanical models, on ly few experimental works have tried to verify it. From these studies, cont radictory results have been found. Moreover, it has recently been noted tha t no such experimental verification has been performed for ligament tissues . In this paper, an experimental method is developed to test the hypothesis of variables separation. This method is then used with human cruciate liga ments and patellar tendons. It is shown that the use of the variables separ ation hypothesis is justified at least for strain values lower than 16% for anterior cruciate ligament, lower than 12% for posterior cruciate ligament and lower than 6% for patellar tendon. The method presented in this paper could be used to verify the validity of variables separation for other tiss ues, (C) 2000 Elsevier Science Ltd. All rights reserved.