Activation of human quadriceps femoris during isometric, concentric, and eccentric contractions

Abstract

Maximal and submaximal activation level of the right knee-extensor muscle group were studied during isometric and slow isokinetic muscular contractions in eight male subjects. The activation level was quantified by means of the twitch interpolation technique. A single electrical impulse was delivered, whatever the contraction mode, on the femoral nerve at a constant 50 degrees knee flexion (0 degrees = full extension). Concentric, eccentric (both at 20 degrees /s velocity), and isometric voluntary activation levels were then calculated. The mean activation levels during maximal eccentric and maximal concentric contractions were 88.3 and 89.7%, respectively, and were significantly lower (P < 0.05) with respect to maximal isometric contractions (95.2%). The relationship between voluntary activation levels and submaximal torques was linearly fitted (P < 0.01): comparison of slopes indicated lower activation levels during submaximal eccentric compared with isometric or concentric contractions. It is concluded that reduced neural drive is present during 20 degrees /s maximal concentric and both maximal and submaximal eccentric contractions. These results indicate a voluntary activation dependency on both tension levels and type of muscular actions in the human knee-extensor muscle group.

Assessing Voluntary Muscle Activation with the Twitch Interpolation Technique

“…In contrast, significant deficits in quadriceps femoris activation have been reported during both concentric and eccentric isokinetic actions [16,76] . Furthermore, significant differences in quadriceps femoris activation have been found between dynamic and isometric efforts [16,76] .…”

“…In contrast, significant deficits in quadriceps femoris activation have been reported during both concentric and eccentric isokinetic actions [16,76] . Furthermore, significant differences in quadriceps femoris activation have been found between dynamic and isometric efforts [16,76] . For example, Babault and colleagues reported voluntary activation levels of 95.2 ± 1.2% for isometric contractions, 88.3 ± 1.9% for eccentric contractions at 20°.s -1 and 89.7 ± 1.4% for concentric contractions at the same angular velocity (means ± standard errors) [76] .…”

“…To accommodate for the changes in voluntary force that occur during dynamic contractions the force trace prior to stimulation is extrapolated to provide an estimate of what the voluntary force would have been at the time when evoked force reaches its peak [16,76,77] . This extrapolation method has been shown to have a negligible impact on estimates of voluntary activation during isometric contractions [14] .…”

“…Furthermore, significant differences in quadriceps femoris activation have been found between dynamic and isometric efforts [16,76] . For example, Babault and colleagues reported voluntary activation levels of 95.2 ± 1.2% for isometric contractions, 88.3 ± 1.9% for eccentric contractions at 20°.s -1 and 89.7 ± 1.4% for concentric contractions at the same angular velocity (means ± standard errors) [76] . These studies suggest, for the quadriceps muscles at least, that the levels of activation reported during isometric actions are not necessarily indicative of those that 20 might occur in dynamic contractions.…”

Preservation of eccentric strength in older adults: Evidence, mechanisms and implications for training and rehabilitation

“…Increased antagonist activation during concentric contractions-The preservation of eccentric strength may also be explained by the disproportionate activation of antagonist muscles with aging reported in some (Macaluso et al, 2002;Hakkinen et al, 1998) but not all (Babault et al, 2001;Valour et al, 2003) studies. While it remains to be determined what mechanisms account for this increased coactivation (Hortobagyi and DeVita, 2006), a greater activation of antagonist muscles, specifically during concentric contractions, could contribute to the greater deficits in concentric strength observed in older adults ( fig.…”