B-17 Thematic Poster - Physical Activity and Cognition

Abstract

PURPOSE: Ultra-marathon running offers the unique possibility to investigate the human body when pushed towards its endurance limitations. From investigations looking at locomotor muscle fatigue it is well established that central fatigue (i.e. a reduced drive to a muscle) is a major contributor to the loss in leg muscle strength found after ultra-endurance exercise. Only limited data is available on respiratory muscle strength after an ultra-marathon showing a large variability in the reduction of maximal voluntary inspiratory (MIP) and expiratory (MEP) pressures. Whether this reduction is caused by peripheral and/or central fatigue is currently unknown. METHODS: We assessed respiratory muscle strength by measuring MIP and MEP (n=22) as well as mouth twitch pressure (Pm,tw) and voluntary activation ratio (VAR, n=16) measured by cervical magnetic stimulation before and after a 103 km mountain ultra-marathon with ∼6000 m of positive and negative elevation. Lung function parameters and maximal voluntary ventilation (MVV) were also obtained at similar time points. RESULTS: Both MIP (-16±13%) and MEP (-21±14%) were significantly reduced after the race likely due to substantial peripheral fatigue (reduction in Pm,tw: -19±15%, p<0.01) while VAR (-3±6%, p=0.09) only tended to be decreased suggesting no or only modest levels of central fatigue. No change was observed for forced vital capacity while forced expiratory volume in the 1st second, peak expiratory and inspiratory flow as well as MVV were markedly reduced (p<0.05). CONCLUSIONS: Ultra-endurance running induces respiratory muscle fatigue with significant peripheral inspiratory muscle fatigue but no central fatigue in contrast to results obtained in locomotor muscles. Whether this is due to inherent differences between these muscle groups, their specific load pattern or methodological considerations remains to be clarified.