Fatigue effects of marathon fatigue on neuromuscular performance. I. Changes in muscle force and stiffness characteristics

International audienceNine experienced endurance runners performed individual marathon runs that involved several tests of neuromuscular performance before, during and after the marathon. The tests were performed with special force platform and dynamometer techniques. The results showed an overall decrease in performance from the marathon. The maximal sprint velocity decreased parabolically during the marathon, reaching the final value of 84% of the pre-marathon one. Similarly, the other test results after marathon indicated that maximal isometric knee extension torque was 78%, the performance in a special rebound test (drop jump) 84% and the 5-jump performance 92% of the pre-marathon values. These reductions were accompanied by alteration in the ground reaction force curves in the sprint and jump tests, suggesting reduced tolerance to stretch load as well as loss in the recoil characteristics of the muscles. Repeated strech-shortening cycle (SSC) exercises induce fatigue that is likely to affect force production both in isometric and dynamic type performances. In fact, force reduction has been demonstrated in prolonged exercises of primarily aerobic type such as 85-km skiing race (1) or marathon running (2) as well as in shorter periods of intensive repetition with the arm muscles (3). Because of the successive stretching loads, the decreased performance may result partly from alterations in stiffness regulation. Thus, repeated and fatiguing SSC efforts may modify neuromuscular behavior so that, depending on the test load, the regulation either increases the muscle stiffness or favors damping mechanisms. These changes may be specifically reflected by disturbances in the interaction person-(shoe)-surface. To investigate further the effects and adaptations induced by this type of fatigue, we examined the short-term influences of a marathon race. The run was performed individually in a research situation, simulating as closely as possible a real competitive race. The parameters covered several aspects of neuromus-cular functioning. This report deals primarily with the force production measured by the dynamom-eter and force platform techniques