Knee Extensor Fatigue Threshold Is Related to Whole-Body V[spacing dot above]O2max.

• Autores: Cornelius J. de Ruiter, Arnold de Haan, Ellen A. Maas, Mariska G. H. Wesseling
• Localización: Medicine & Science in Sports & exercise: Official Journal of the American College of Sports Medicine, ISSN 0195-9131, Vol. 44, Nº. 7, 2012, págs. 1366-1374
• Idioma: inglés
• Texto completo no disponible (Saber más ...)
• Resumen

  • AB Purpose: Above a given exercise intensity, rapid muscle fatigue will occur. We explored the possibility of assessing torque threshold for peripheral fatigue during single-legged repetitive isometric knee extensor exercise. We hypothesized this fatigue threshold to be related to the general aerobic fitness level and the so-called "critical torque" (CT) established with a recently validated 5-min all-out test. Methods: Seventeen healthy men (V[spacing dot above]O2max = 44.7-69.6 mL[middle dot]kg-1[middle dot]min-1) performed six submaximal (20%-55% maximal voluntary contraction [MVC]) 5-min bouts of 60 repetitive contractions (3-s on, 2-s off). Torque was changed between bouts in steps of 5% MVC to estimate the highest intensity (fatigue threshold) at which average changes in rsEMG, EMG median power frequency, and tissue deoxygenation (near-infrared spectroscopy) of the three superficial knee extensor muscles were still <5%, signifying steady-state exercise with minimal peripheral fatigue. On another occasion, one bout was performed in an all-out manner with end-test torque representing CT. Results: Fatigue threshold (40.0% +/- 8.1% MVC) was related (r2 = 0.57, P < 0.05) to CT (53.1% +/- 10.0% MVC), but it was consistently lower (P < 0.05) and only fatigue threshold was significantly related to V[spacing dot above]O2max (r2 = 0.68), and the first (r2 = 0.45) and second (r2 = 0.63) ventilatory threshold obtained during cycle ergometry. Conclusions: Performing submaximal bouts of knee extensor contractions, while monitoring EMG and deoxygenation, seems a feasible manner to estimate an aerobic capacity-related exercise intensity of peripheral fatigue onset. This test may be used to evaluate changes in endurance capacity of single muscle groups, without the necessity for all-out testing, which could be problematic with frail subjects. (C)2012The American College of Sports Medicine