Tillin, N. A. | Search bioRxiv

bioRxiv2024

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

ObjectiveTo 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. MethodsIn 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 Pearsons r correlations, assessing relationships across participants. MEP and silent period duration were compared (ANOVA) between the different phases and at MVC plateau. ResultsMEP and RTD were correlated across separate contractions within participants (RmCorr r=0.43), and in the middle phase across participants (Pearsons 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). ConclusionThe 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.

physiology↗

bioRxiv2024

Test-retest reliability of TMS motor evoked responses and silent periods during explosive voluntary isometric contractions.

PurposeThis study assessed the intraclass correlation coefficient (ICC) and coefficient of variation (CV) test-retest reliability of TMS responses MEPs and silent periods at early, middle, and late phases of the rising time-torque curve during explosive voluntary contractions. We also investigated how the number of consecutively averaged measurements over 3 to 15 separate contractions influenced reliability. MethodsOn two separate occasions 3-7 days apart, 14 adults completed 48 isometric explosives (1-s) contractions of the knee extensors, superimposed with TMS. The TMS elicited an MEP and silent period in the quadriceps muscles at 45 (early), 115 (middle), or 190 ms (late) during each contraction. TMS was also superimposed at the plateau of 15 separate MVCs. Test-retest ICC and CV were calculated for consecutively averaged MEPs and silent periods. ResultsNo one condition was more reliable than another. For MEP amplitude, in all conditions except the explosive late phase, ICCs generally increased, and CV decreased, with an increase in the number of averaged contractions, and were >0.50 ICC and <15% CV within 7 contractions. For silent period, ICCs and CVs were unaffected by the number of consecutively averaged contractions and remained >0.50 ICC and <10% CV. ConclusionTest-retest reliability of TMS responses is comparable between phases of explosive contraction and at the plateau of MVC. To enhance MEP reliability, with the increases he number of averaged contractions of except the explosive late phase, we recommend studies average data across > the 3-5 contractions typically reported in the literature for studies using TMS during MVCs.

physiology↗