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

Purpose This 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. Methods On 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. Results No 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 0.50 ICC and <10% CV. Conclusion Test-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.