Quadriceps activation and perceived exertion during a high intensity, steady state contraction to failure

The ability to sustain a high-intensity, steady-state muscle contraction ma y have differential effects on neuromuscular activation and perceived exert ion. The purpose of this study was to examine changes in neuromuscular acti vation and perceived exertion at a near-maximal steady-state contraction of the quadriceps in healthy men. Seventeen healthy, college-aged male volunt eers were studied during isometric contractions equivalent to 80% of the ma ximum voluntary contraction (MVC). Perceived exertion was measured with a m odified category-ratio scale (CR-10). The CR-10 scale was anchored with one high anchor at 100% MVC and one low anchor at 10% MVC, Subjects then perfo rmed an 80% MVC for as long as they could sustain it. Subjects were asked t o rate the feelings in their quadriceps every 5 s during the contraction. T he results demonstrated significant increases in neuromuscular activation o f the vastus medialis and vastus lateralis muscles (P < 0.05) during the 80 % MVC, but there were no significant muscle by time interactions. The resul ts also demonstrated a significant increase (P < 0.05) in perceived exertio n during the 80% MVC. Neuromuscular activation of both muscles, and perceiv ed exertion, were found to increase in linear (P < 0.05) and quadratic (P < 0.05) trends. Alterations in motor unit discharge properties or impairment s in muscle fiber membrane excitability may account for nonlinear increases in vastii muscle activation and perceived exertion. (C) 2000 John Wiley & Sons, Inc.