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We compared different approaches to analyze running mechanics alterations during repeated treadmill sprints. Thirteen active male athletes performed five 5-second sprints with 25 seconds of recovery on an instrumented treadmill. This approach allowed continuous measurement of running kinetics/kinematics and calculation of vertical and leg stiffness variables that were subsequently averaged over 3 distinct sections of the 5-second sprint (steps 2–5, 7–10, and 12–15) and for all steps (steps 2–15). Independently from the analyzed section, propulsive power and step frequency decreased with fatigue, while contact time and step length increased (P < .05). Except for step frequency, all mechanical variables varied (P < .05) across sprint sections. The only parameters that highly depend on running velocity (propulsive power and vertical stiffness) showed a significant interaction (P < .05) between the analyzed sections, with smaller magnitude of fatigue-induced change observed for steps 2–5. Considering all steps or only a few steps during early, middle, or late phases of 5-second sprints provides similar mechanical outcomes during repeated treadmill sprinting, although acceleration induces noticeable differences between the sections studied. Furthermore, quantifying mechanical alterations from the early acceleration phase may not be readily detectable, and is not recommended.
Olivier Girard, Franck Brocherie, and Grégoire P. Millet are with ISSUL, Institute of Sport Sciences, Department of Physiology, Faculty of Biology and Medicine, University of Lausanne, Switzerland. Olivier Girard is also with the Athlete Health and Performance Research Center, Aspetar, Qatar Orthopaedic and Sports Medicine Hospital, Doha, Qatar. Jean-Benoit Morin is with the Laboratory of Human Motricity, Education Sport and Health (LAMHESS), University of Nice Sophia Antipolis, Nice, France. Francis Degache is with the University of Health Sciences, University of Applied Sciences and Arts Western Switzerland, Lausanne, Switzerland.