Knee extensor torque, work, and EMG during subjectively graded dynamic contractions

Abstract

We examined knee extensor peak torque, work, and electromyogram (EMG) during dynamic contractions to perceived exertion levels in men and women. Thirty subjects performed three maximal effort isokinetic knee extensions (60 deg x s(-1)), followed by three contractions to each of nine separate levels of perceived exertion. Surface EMG of the vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF), and knee extensor peak torque and work were normalized to a percent of each respective value obtained during the maximal effort contractions. The results demonstrated a significant linear increase in voluntary knee extensor peak torque and work across perceived exertion levels. Knee extensor peak torque and work were less than 70%, 80%, and 90% maximal voluntary contraction (MVC) at perceived exertion levels 7, 8, and 9, respectively. A significant increase in VM, VL, and RF muscle EMG was observed across perceived exertion levels 1 through 9, with EMG increase highest for the VL. The findings demonstrate that dynamic contractions guided by perceived exertion are underproduced at relatively high perceptual intensities, and that reliance on VL activation occurs across submaximal torque levels. The overestimation of knee extensor peak torque and work at relatively high perceptual intensities may suggest the presence of a subconscious mechanism aiming to reduce high muscle and joint forces.

Contraction mode shift in quadriceps femoris muscle activation during dynamic knee extensor exercise with increasing loads

“…This finding is in contrast to previous investigations that reported either similar IEMG-torque responses between men and women during isokinetic (concentric) knee extensor exercise of progressive increased efforts (Pincivero et al, 2003), or greater overall activation values for women during the concentric mode of repeated inertial contractions at 50% 1RM (Pincivero et al, 2006). In order to further elucidate patterns of muscle activation, the EMG median frequency parameter has been examined under conditions of muscle fatigue (Bilodeau et al, 2003;Arendt-Nielsen et al, 1989;Gerdle et al, 1997) and incremental force levels (Cioni et al, 1994;Mullany et al, 2002;Pincivero et al, 2001Pincivero et al, , 2002.…”

“…As a result, the analysis of the raw EMG signal in its frequency domain may reveal a propensity of higher values in men, than women (Cioni et al, 1994;Pincivero et al, 2001Pincivero et al, , 2002. However, in terms of examining EMG amplitude during submaximal knee extensor exercise, when normalized to an individuals' maximal voluntary contraction, differences between men and women may not be evident (Pincivero et al, 2003). Therefore, the objective of the present study was to examine the surface EMG-contraction intensity relation of the different QF muscle components during different modes (i.e., concentric, isometric and eccentric) of dynamic knee extension exercise between healthy young men and women.…”

“…Therefore, the objective of the present study was to examine the surface EMG-contraction intensity relation of the different QF muscle components during different modes (i.e., concentric, isometric and eccentric) of dynamic knee extension exercise between healthy young men and women. It was hypothesized that: (1) VL muscle EMG amplitude will be greater than the VM and RF muscles during all modes of knee extension exercise across lowto-moderate lifting loads, while converging at near-maximal loads (Alkner et al, 2000;Pincivero et al, 2003;Pincivero and Coelho, 2000), (2) men and women will demonstrate similar QF muscle EMG amplitudes across all contraction modes and loads (Pincivero et al, 2003), and (3) VL muscle f med will increase more in men than women across the spectrum of lifting loads, whereas VM and RF muscle f med will not display lifting load dependency (Cioni et al, 1994;Pincivero et al, 2001Pincivero et al, , 2002.…”

Perceptions of effort during handgrip and tongue elevation in Parkinson's disease

“…The observed function is characterized by relatively larger differences in pressure at the effort extremes and little difference in pressure across the midrange effort levels. Similarly, Pincivero et al [32] described a relatively linear relationship in the midrange, but not at the extremes, of perceived exertion for knee-extension in normal adults. Another major finding from the study by Somodi et al [17] was that higher levels of effort corresponded with lower pressure values for the hand than for the tongue.…”

Submaximal force production during perceptually guided isometric exercise

“…The reason for perceptual overestimation may be a teleological one, in that subjects subconsciously under produce force at higher intensities as a protective mechanism, in order to maintain a reserve capacity and therefore prevent mechanical and metabolic damage which may occur from maximal force generation. Another explanation for the perceptual inaccuracies may be the absence of an anchoring process, which allows the subjects to cognitively establish a perceptual range by a low and a high reference (Pincivero et al 2003a(Pincivero et al , 2003b In the present study we introduced two different fatiguing protocols, a maximal 100% MVC and a submaximal 20% MVC fatigue test. Central and peripheral fatigue has been shown to develop during maximal and submaximal sustained voluntary muscle contractions (Bigland-Ritchie et al 1983).…”