Cassio Ruas

and 4 more

We compared voluntary drive and corticospinal responses during eccentric (ECC), isometric (ISO) and concentric (CON) muscle contractions to shed light on the mechanisms underpinning the greater force production despite lower electromyographic activity (EMG) commonly reported in ECC than ISO and CON. Sixteen participants (20-33 y) performed ISO and isokinetic (30˚/s) CON and ECC knee extensor contractions between 110˚ and 40˚ knee flexion, while EMG was recorded from vastus lateralis. Voluntary activation (VA) was measured during ISO, CON and ECC maximal voluntary contractions (MVCs). Transcranial magnetic stimulation elicited motor evoked potentials (MEPs) and corticospinal silent periods (CSP) during MVCs and submaximal contractions (30% maximum), and short-interval intracortical inhibition (SICI) in submaximal contractions. MVC torque was greater (P<0.01) during ECC (302.6±90.0 Nm) than ISO (269.8±81.5 Nm) and CON (235.4±78.6 Nm), but VA was lower (P<0.01) for ECC (68.4±14.9%) than ISO (78.3±13.1%) and CON (80.7±15.4%). Additionally, EMG/torque was lower (P<0.02) for ECC (1.9±1.1 μV.Nm-1) than ISO (2.2±1.2 μV.Nm-1) and CON (2.7±1.6 μV.Nm-1), CSP was shorter (p<0.04) for ECC (0.097±0.03 s) than ISO (0.109±0.02 s) and CON (0.109±0.03 s), and MEP amplitude was lower (P<0.01) for ECC (3.46±1.67 mV) than ISO (4.21±2.33 mV) and CON (4.01±2.06 mV). Similar results were found for EMG/torque and CSP during 30% contractions, but MEP amplitude and SICI showed no differences among contractions (p>0.05). Reduced VA during ECC may be at least partly explained by lower corticospinal excitability, while a shorter CSP may reflect extra muscle spindle excitation of the motoneurons from muscle lengthening, rather than reduced corticospinal inhibition.