Training induced changes in quadriceps activation during maximal eccentric contractions

Abstract

Despite full voluntary effort, neuromuscular activation of the quadriceps group of muscles appears inhibited during eccentric contractions. A nerve stimulation protocol during dynamic contractions of the quadriceps was developed that employed triplets of supramaximal pulses to assess suppressed eccentric activation. Subsequently the effects of a short training intervention, performed on a dynamometer, on eccentric strength output and neural inhibition were examined. Torque-angular velocity (T-ω) and experimental voluntary neural drive-angular velocity (%VA-ω; %VA, obtained via the interpolated twitch technique) datasets, were obtained from pre- and post-training testing sessions. Non-linear regression fits of a seven parameter torque function and of a 3rd degree polynomial were performed on the pre- and post-training T-ω and %VA-ω datasets respectively. T-test showed a significant (p < 0.05) increase in the overall torque output post-training for the group, with three out of the six subjects demonstrating a significant (p < 0.05) increase in the torque output across the range of angular velocities as shown by the extra-sum-of-squares F-test. A significant increase (p < 0.05) in the %VA post-training was also observed as well as a reduction in the plateauing of the torque output during fast eccentric contractions.