Introduction In the literature it is often mentioned that during given movements the whole energy delivered by the muscle can be enhanced by means of strain energy stored in tendons and aponeuroses (Alexander and Bennet-Clark, 1977; De Haan et al., 1989; Ettema et al., 1990). Further, the non rigidity of the tendon and aponeurosis is relevant for the work producing capability of the muscle fibre and for the motion and performance of the human body (Alexander, 1988; Ettema et al., 1990). Basing on these findings we hypothesised, that sprinting performance is related to elongation and maximal energy storage capacity of the triceps surae and quadriceps tendon and aponeuroses due to the high forces exerted during the sprint. Therefore this study aimed to examine the mechanical properties of the triceps surae and quadriceps muscle-tendon-units on sprinters with different sprinting performance. Methods Twenty eight sprinters (body mass: 78.04 +/- 6.19 kg, height: 184.4 +/- 6.1 cm) participated in the study. All subjects performed maximal isometric voluntary plantarflexion and knee extension contractions of their left leg on a dyna-mometer. During the plantarflexion the ankle angle was set at 90° ‹ having the knee fully extended. For the knee ex-tension the knee angle was set at 115°‹ and the hip angle at 140° ‹. The kinematics of the leg were recorded using a Vicon system (8 cameras 120 Hz) to allow the calculation of the corresponding resultant joint moments. The distal aponeurosis of the gastrocnemius medialis or the vastus lateralis during plantar flexion or knee extension respec-tively were visualised by ultrasound (Aloka SSD 4000). The elongation, strain, energy storage capacity, stiffness and force of both tendons and aponeuroses were determined. Cluster analysis was used to divide the subjects into two groups according to their best 100 m time (fast group: 11.04 +/- 0.17 s n=17; slow group: 11.64 +/- 0.23 s n=11). The differences between the groups were tested for all measured parameter using an independent sample t-test. Results No differences in any of the examined parameters of the triceps surae muscle-tendon-unit were found (Fig. 1). In the fast group the tendon and aponeurosis of the vastus lateralis showed significant greater elongation (32.9 +/- 7.0 vs. 26.9 +/- 5.8 mm, p.0.05) and strain (9.02 +/- 1.5 vs. 7.74 +/- 1.6 %, P.0.05) than the slow group (Fig.2). No further differ-ences between the groups (p>0.05) were found for the quadriceps tendon: Maximal force (4332 +/- 812 vs. 3886 +/- 829 N), maximal energy storage capacity (131.0 +/- 43.5 vs. 124.7 +/- 38.8 J/m) and stiffness (50.23 +/- 7.51 vs. 54.85 +/-14.0 kN/strain). Discussion/Conclusion The main findings of this study are: (a) Both sprinter groups showed similar mechanical properties for their triceps surae muscle tendon unit and (b) for the sprinters of the fast group the tendon and aponeurosis of the vastus lateralis exhibited an average of 16% higher maximal strain and 22 % higher elongation than those of the slow group. The higher maximal strain and elongation of the quadriceps tendon and aponeurosis in the fast group might decrease the shortening velocity of the muscles fibres increasing the force potential of the muscle-tendon-unit due to the force velocity relationship and in consequence increase the rate of force generation per active muscle volume. The above cited points suggest that the higher maximal elongation and strain of the quadriceps tendon and aponeurosis contrib-ute to the differences in sprinting performance between both examined groups.
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