## 2 Materials and Methods  
In the present study, 268 tendons from 35 human cadavers were examined. From every cadaver, the following types of tendon were harvested: 67-67 pieces quadriceps and peroneus longus (PL), 69 pieces semitendinosus + gracilis (STG) and 65 pieces tibialis anterior (TA) tendons. The types of tendon grafts were collected from human cadavers within 24 h post mortem. All tendons were visually inspected before mechanical testing, and the cortexes of the dead were also examined. Each graft was soaked in a radioprotective solution for 4 h at 40 \({}^{\circ}\)C with agitation and then for 24 h at 4 \({}^{\circ}\)C, according to [PERSON] et al. [13], to help prevent the harmful effects of sterilization and storage on the tissue. The solution contained 2.7% D-mannitol, 3.8% D-trehalose, 16.7% 1,2-propanediol and 24.2% dimethyl-sulfoxide (all _w/w_, manufacturer: Sigma-Aldrich, Saint Louis, MO, USA). Each specimen was labeled in a separate container. The grafts were then divided into three groups. Group A contained 63 fresh specimens (16 quadriceps, 17 semitendinosus + gracilis, 14 tibialis anterior, 16 peroneus longus, the average age of the donors was \(78.4\pm 15.69\) years). The other groups of tendons were frozen slowly to \(-80\)\({}^{\circ}\)C. Group B (22 quadriceps, 22 semitendinosus + gracilis, 22 tibialis anterior, 22 peroneus longus, the average age of donors was \(85.2\pm 15.31\) years) were sterilized with a bactericidal dose (target dose: 21 kGy, dose range: 18-24 kGy). Group C contained the other 117 tendons (29 quadriceps, 30 semitendinosus + gracilis, 29 tibialis anterior, 29 peroneus longus, the average age of donors was 77.8 \(\pm\) 20.61 years) sterilized with a virucidal dose (target dose: 42 kGy, dose range: 38-46 kGy). The exact numbers for the distribution between the groups were based on cadaver availability and the number of successfully harvested, intact tendons, bearing in mind having a statistically significant number of tendons in each tested group. According to the results of a preliminary study [11], the freezing, the irradiation, and thawing were unified at all graft types. Irradiation was performed on frozen grafts, with the same method atall grafts. Before the test, the tendons were thawed at 37 \({}^{\circ}\)C for 20 min. Prior to the start of the test, the cross-section of the tendons and the length of the clamp were measured with micrometric calipers. For the endurance tests, we used an Instron 8872 servohydraulic load frame (Instron Ltd., High Wycombe, UK) equipped with an Instron Dynacell load cell with a 25 kN load capacity and an Instron Fasttrack 8800 control unit and a freezer clamp structure at the accredited materials testing laboratory of the Budapest University of Technology and Economics Biomechanical Research Center. The strain characteristics of the specimens were also investigated by a Mercury Monet (Sobriety, Kurim, Czech Republic) optical digital image correlation (DIC) machine. During the preliminary tests, three minutes of freezing was used for proper fixation and for preventing the freezing of the grafts at the gauge length [12]. Based on our previous result [12], the effect of frost had a negligible effect on the measuring length because the thermal conductivity of the tissue is weak. The force-elongation curve was determined after 1000 cycles at a frequency of 2 Hz between 50 and 250 N. The method of the load-to-failure test is summarized in [12]. The cross-section of the specimen was measured by a digital caliper, and the strain (crosshead displacement) and force were measured by the tensile tester for the calculation of the presented results. The tests were authorized by the Research Ethics Committee of Uzsoki utcai and Peterffy Sandor Hospital (license number: 03/2009). Comparing biological materials is not easy, as there is a big difference between humans, including their tissues. Therefore, for statistical comparison, a nonparametric procedure had to be used to see if the samples could be derived from the same distribution.