title: Influence of neural adjustments and muscle oxygenation on task failure during sustained isometric contractions with elbow flexor muscles.
abstract: This study investigated the adjustments in muscle activation and oxygenation in biceps and triceps brachii during two tasks sustained to failure at 20 and 60% of the maximal voluntary contraction (MVC) force. The tasks required participants either to push against a rigid restraint (force task) or to support an inertial load (position task) with the elbow flexor muscles. The surface EMG was recorded for biceps brachii, brachioradialis, triceps brachii and trapezius superior muscles. Muscle oxygenation of biceps and triceps brachii was measured by near-infrared spectroscopy. The position task was briefer (404 ± 159 s) than the force task (533 ± 194 s) when performed at 20% MVC (P = 0.011), but endurance time did not differ at 60% MVC (54 ± 19 versus 64 ± 16 s, respectively; P = 0.13). Biceps brachii oxygenation decreased slightly (by ~7%) during tasks performed at 20% MVC, whereas it dropped (-40%) for tasks sustained at 60% MVC. However, the decrease in muscle oxygenation was not a significant predictor of time to failure at the two target forces, although its contribution to muscle fatigue cannot be completely ruled out at 60% MVC. In contrast, time to failure was predicted by the increase in EMG of biceps brachii for both tasks at 20% MVC, and EMG of brachioradialis and trapezius for both tasks at 60% MVC. These results suggest that neural adjustments rather than muscle oxygenation limited the time to failure for the force and position tasks at low and high target forces.
authors.affiliation: Laboratory of Applied Biology, Université Libre de Bruxelles, 808 route de Lennik, 1070 Brussels, Belgium.
authors.forename: Cédric
authors.initials: C
authors.lastname: Booghs
authors.forename: Stéphane
authors.initials: S
authors.lastname: Baudry
authors.forename: Roger
authors.initials: R
authors.lastname: Enoka
authors.forename: Jacques
authors.initials: J
authors.lastname: Duchateau
mesh_terms: D000293:Adolescent; D000328:Adult; D004550:Elbow / Q000098:blood supply / Q000502:physiology*; D004576:Electromyography; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology; D018482:Muscle, Skeletal / Q000098:blood supply / Q000294:innervation / Q000502:physiology*; D010100:Oxygen / Q000097:blood*; D010807:Physical Endurance / Q000502:physiology; D019265:Spectroscopy, Near-Infrared; D055815:Young Adult
chemical_list: D010100:Oxygen