Resumen de The Reliability of the Interpolated Twitch Technique During Submaximal and Maximal Isometric Muscle Actions

Michael A. Cooper, Trent J. Herda, Pablo B. Costa, Eric D. Ryan, Joel T. Cramer

• The purpose of this study was to examine the test-retest reliability of the percent voluntary activation (%VA) vs. force relationships. Fourteen healthy men (mean ± SD age = 21 ± 2.6 years) and 8 women (age = 21 ± 1.8 years) completed 4 maximal voluntary contractions (MVCs) and 9 randomly ordered submaximal isometric plantar flexions from 10 to 100% of the MVC. Transcutaneous electrical stimuli were delivered to the tibial nerve using a high-voltage constant-current stimulator (DS7AH; Digitimer, Herthfordshire, United Kingdom). The %VA was calculated for each maximal and submaximal MVC. Paired-samples t-tests were used to quantify systematic variability, whereas the intraclass correlation coefficients (ICCs), standard error of the mean (%SEM), and minimum differences (%MD; expressed as a percentage of the means) were used for test-retest reliability. Systematic variability was not present at any of the contraction intensities (p > 0.05). The ICCs ranged from 0.52 to 0.84, whereas the %SEM ranged from 6.75 to 38.45%, and the %MD ranged from 18.71 to 106.58%. The ICCs were >=0.74 at contraction intensities ranging from 40 to 100% MVC (6.75�16.78% SEM), whereas the ICCs were <=0.65 (20.95�38.45% SEM) for the contraction intensities <=30% MVC. Although not statistically tested, the ICCs tended to be higher, whereas the %SEMs lower for contractions >=40% MVC. Future research using %VA during submaximal contraction intensities to predict a true maximal force may want to exclude contraction intensities <40% MVC. In addition, caution is warranted when interpreting the changes in the %VA during MVCs after an experimental intervention.