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PLoS One. 2016 Mar 31;11(3):e0151687. doi: 10.1371/journal.pone.0151687. eCollection 2016.

Effect of the Fatigue Induced by a 110-km Ultramarathon on Tibial Impact Acceleration and Lower Leg Kinematics.

Author information

Laboratory of Exercise Physiology (EA4338), University Savoie Mont Blanc, Le Bourget-du-Lac, France.
Laboratory Culture Sport Health Society (EA 4660), University of Franche-Comté, Besançon, France.
Laboratory of Exercise Physiology (EA4338), University of Lyon, Saint-Etienne, France.
Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Canada.
Institut de Recherche Biomédicale des Armées (IRBA), Fatigue and Vigilance Team, Brétigny-sur-Orge, France.
Laboratoire des Adaptations Métaboliques à l'Exercice en conditions Physiologiques et Pathologiques (EA3533), Université Blaise Pascal Clermont Auvergne, Clermont-Ferrand, France.
Laboratory of Human Motricity, Education Sport and Health (EA6312), University of Nice Sophia Antipolis, Nice, France.


Ultramarathon runners are exposed to a high number of impact shocks and to severe neuromuscular fatigue. Runners may manage mechanical stress and muscle fatigue by changing their running kinematics. Our purposes were to study (i) the effects of a 110-km mountain ultramarathon (MUM) on tibial shock acceleration and lower limb kinematics, and (ii) whether kinematic changes are modulated according to the severity of neuromuscular fatigue. Twenty-three runners participated in the study. Pre- and post-MUM, neuromuscular tests were performed to assess knee extensor (KE) and plantar flexor (PF) central and peripheral fatigue, and a treadmill running bouts was completed during which step frequency, peak acceleration, median frequency and impact frequency content were measured from tibial acceleration, as well as foot-to-treadmill, tibia-to-treadmill, and ankle flexion angles at initial contact, and ankle range of motion using video analysis. Large neuromuscular fatigue, including peripheral changes and deficits in voluntary activation, was observed in KE and PF. MVC decrements of ~35% for KE and of ~28% for PF were noted. Among biomechanical variables, step frequency increased by ~2.7% and the ankle range of motion decreased by ~4.1% post-MUM. Runners adopting a non rearfoot strike pre-MUM adopted a less plantarflexed foot strike pattern post-MUM while those adopting a rearfoot strike pre-MUM tended to adopt a less dorsiflexed foot strike pattern post-MUM. Positive correlations were observed between percent changes in peripheral PF fatigue and the ankle range of motion. Peripheral PF fatigue was also significantly correlated to both percent changes in step frequency and the ankle angle at contact. This study suggests that in a fatigued state, ultratrail runners use compensatory/protective adjustments leading to a flatter foot landing and this is done in a fatigue dose-dependent manner. This strategy may aim at minimizing the overall load applied to the musculoskeletal system, including impact shock and muscle stretch.

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