Purpose: Ultra-marathon running offers the unique possibility to investigate the mechanisms contributing to the limitation of endurance performance. Investigations of locomotor muscle fatigue show that central fatigue is a major contributor to the loss of strength in lower limbs after an ultra-marathon. Also respiratory muscle fatigue is known to limit exercise performance but only limited data are available on changes in respiratory muscle function after ultra-marathon running and it is not known whether the observed impairment is caused by peripheral and/or central fatigue.
Method: In 22 experienced ultra-trail runners, we assessed respiratory muscle strength, i.e. maximal voluntary inspiratory (MIP) and expiratory (MEP) pressures, mouth twitch pressure (Pm,tw, n=16) and voluntary activation (%VA, n=16) by means of cervical magnetic stimulation, lung function and maximal voluntary ventilation (MVV), before and after a 110-km mountain ultra-marathon with 5862m of positive elevation gain.
Results: Both MIP (-16+/-13%) and MEP (-21+/-14%) were significantly reduced after the race. Fatigue of inspiratory muscles likely resulted from substantial peripheral fatigue (reduction in Pm,tw: -19+/-15%, P < 0.01) as %VA (-3+/-6%, P = 0.09) only tended to be decreased suggesting negligible or only mild levels of central fatigue. Forced vital capacity remained unchanged while forced expiratory volume in 1 s, peak inspiratory and expiratory flow rate as well as MVV were significantly reduced (P < 0.05).
Conclusions: Ultra-endurance running reduces respiratory muscle strength, for inspiratory muscles shown to result from significant peripheral muscle fatigue with only little contribution of central fatigue. This contrasts findings in locomotor muscles. Whether this difference between muscle groups results from inherent neuromuscular differences, their specific pattern of loading or other reasons remains to be clarified.
(C) 2014 American College of Sports Medicine