title: Locomotor muscle fatigue increases cardiorespiratory responses and reduces performance during intense cycling exercise independently from metabolic stress.
abstract: Locomotor muscle fatigue, defined as an exercise-induced reduction in maximal voluntary force, occurs during prolonged exercise, but its effects on cardiorespiratory responses and exercise performance are unknown. In this investigation, a significant reduction in locomotor muscle force (-18%, P < 0.05) was isolated from the metabolic stress usually associated with fatiguing exercise using a 100-drop-jumps protocol consisting of one jump every 20 s from a 40-cm-high platform. The effect of this treatment on time to exhaustion during high-intensity constant-power cycling was measured in study 1 (n = 10). In study 2 (n = 14), test duration (871 +/- 280 s) was matched between fatigue and control condition (rest). In study 1, locomotor muscle fatigue caused a significant curtailment in time to exhaustion (636 +/- 278 s) compared with control (750 +/- 281 s) (P = 0.003) and increased cardiac output. Breathing frequency was significantly higher in the fatigue condition in both studies despite similar oxygen consumption and blood lactate accumulation. In study 2, high-intensity cycling did not induce further fatigue to eccentrically-fatigued locomotor muscles. In both studies, there was a significant increase in heart rate in the fatigue condition, and perceived exertion was significantly increased in study 2 compared with control. These results suggest that locomotor muscle fatigue has a significant influence on cardiorespiratory responses and exercise performance during high-intensity cycling independently from metabolic stress. These effects seem to be mediated by the increased central motor command and perception of effort required to exercise with weaker locomotor muscles.
authors.affiliation: School of Sport, Health and Exercise Sciences, Bangor University, George Bldg., Holyhead Road, Bangor, Gwynedd, LL57 2PZ, UK. s.m.marcora@bangor.ac.uk
authors.forename: Samuele M
authors.initials: SM
authors.lastname: Marcora
authors.forename: Andrea
authors.initials: A
authors.lastname: Bosio
authors.forename: Helma M
authors.initials: HM
authors.lastname: de Morree
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology*; D001784:Blood Gas Analysis; D002302:Cardiac Output / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008124:Locomotion / Q000502:physiology*; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology; D010101:Oxygen Consumption / Q000502:physiology; D015656:Respiratory Mechanics / Q000502:physiology*; D012649:Self Concept; D013312:Stress, Physiological / Q000378:metabolism / Q000503:physiopathology; D013318:Stroke Volume / Q000502:physiology