Rate of force development is correlated with corticospinal excitability during explosive voluntary contractions.

Objective: To investigate the relationship between rate of torque development (RTD) and corticospinal excitability (denoted by motor-evoked potential; MEP) during explosive voluntary contractions. Also, to assess differences in MEP and silent period duration between different phases of explosive contraction and at maximum voluntary contraction (MVC) plateau. Methods: In 14 adults, quadriceps muscle MEP and silent period duration were measured at ~45 (early), ~115 (middle), and ~190 ms (late) from EMG onset during knee-extensor isometric explosive contractions, and at MVC plateau with superimposed transcranial magnetic stimulation (TMS). RTD was measured immediately prior to early-phase MEP during the same contractions, and these two variables were correlated across separate contractions, within participants, via repeated measures correlation (RmCorr). RTD was also measured in explosive contractions without TMS over early-, middle-, and late-phases and correlated to MEP averaged across the corresponding and preceding phases, via Pearson's r correlations, assessing relationships across participants. MEP and silent period duration were compared (ANOVA) between the different phases and at MVC plateau. Results: MEP and RTD were correlated across separate contractions within participants (RmCorr r=0.43), and in the middle phase across participants (Pearson's r=0.56). MEP and RTD were not correlated in other phases (r≥0.09). Silent period duration increased throughout the different phases of contraction and up to MVC plateau (ANOVA, p= 0.001) but MEP remained constant (ANOVA, p= 0.42). Conclusion: The correlations between MEP and RTD suggests corticospinal excitability is an important determinant of RTD. During rapid torque development and up to MVC plateau, corticospinal inhibition increases but excitability remains constant.