Abstract

VALAMATOS, Maria João; VALAMATOS, Maria José; MIL-HOMENS, Pedro  and  VELOSO, António. Dynamic take-off hurdles clearance: Changes on the mechanical power output variables produced by the muscle-skeletal system on the take-off phase of hurdles clearance, induced by a specially designed fatigue protocol. Rev. Port. Cien. Desp. [online]. 2005, vol.5, n.1, pp.15-30. ISSN 1645-0523.

The purpose of this study was to investigate changes on the mechanical power output variables produced by the muscle-skeletal system on the take-off phase of hurdles clearance, induced by a specially designed fatigue protocol, which was intended to simulate the fatigue condition of the 400 meters hurdles. Seven national elite male athletes (age: 24.43 ± 5.68 years old; height: 1.82 ± 0.06 m; body mass: 71.79 ± 5.84 Kg; 400mH best: 51.55 ± 1.72 s) participated in this study. The performance of the clearance action was high speed video recorded at 250Hz (Redlake PCI1000), and 2D coordinates of the athlete body joints were obtained. The regression equations adapted by Jacobs et al. (14) were used to estimate the length changes of the muscle tendon complex during the contact phase of the take-off of the clearance action. A three axial force platform was installed on the track, and the ground reaction forces (Fz, Fy and Fx) were recorded synchronized with video data. These procedures were repeated before and after a fatigue protocol. The differences between both conditions were tested using T-Tests for paired samples. In the take-off phase of the hurdles clearance there was an increase on the loose of the horizontal velocity in the fatigue conditions (p<.05). This fact was associated with the increase of the total contact time (p<.001), due to a significant increase of both the breaking (p<.001) and the propulsive (p<.05) contact times. However, ground reactions forces did not show any significant changes. The increase of the support time and the changes in angular displacement of the joint of the trail leg, suggested a decrease in the stiffness and power output produced by the muscle-skeletal system, in the fatigue condition.

Keywords : athletics; 400 meters hurdles; kinematics; kinetics; fatigue; stretch-shortening cycle (SSC).

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