RELIABILITY OF MOTOR UNIT RECRUITMENT THRESHOLD VERSUS MEAN FIRING RATE RELATIONSHIPS DURING SUBMAXIMAL CONTRACTIONS

Authors

EM Mosier
MA Trevino
TJ Herda

Abstract

Eric M. Mosier¹, Michael A. Trevino¹ & Trent J. Herda¹

¹University of Kansas, Lawrence, Kansas

PURPOSE: The purpose of this study was to examine the reliability of motor unit (MU) recruitment versus mean firing rate relationships of the vastus lateralis (VL) during 40% and 70% maximal voluntary contractions (MVC). METHODS: Eight healthy men (age=21.63±2.39 yrs) and six healthy women (age=19.67±1.37 yrs) volunteered for this investigation. An electromyography (EMG) sensor was placed over the VL. Participants performed 3 isometric maximal voluntary contractions (MVC) followed by isometric trapezoid muscle actions at 40% and 70% MVC calculated from the highest MVC. These procedures were performed twice separated by 3-5 days. Decomposition techniques were applied to the EMG signals to extract action potentials and firing events of single MUs. The recruitment (REC) thresholds and mean firing rate (MFR) were calculated for each MU. Only MUs that were decomposed with accuracies >90% were included for analysis. Linear regressions were performed on REC vs. MFR relationships on MUs with accuracies >90% and MUs excluding accuracies 90% and again on relationships with the exclusion of MUs with accuracies RESULTS: There were no significant differences between days for the slopes and y-intercepts for either contraction or accuracy condition (including MUs with >90% or excluding MUs with 0.05). The ICCs and SEM (expressed as a percentage of the mean, %) from the 70% MVC that excluded MUs with accuracies 90% were -0.07 and 41.30% and 0.14 and 34.29% for the slopes and 0.56 and 6.86% and 0.38 and 14.39% for the y-intercepts. CONCLUSION: The ICCs and SEMs indicated good reliability for slopes and y-intercepts from the 70% MVC when excluding MUs with accuracies90%, the SEMs were similar to that of the regressions that excluded MUs with accuracies <95%.

Recommended Citation

Mosier, EM; Trevino, MA; and Herda, TJ (2014) "RELIABILITY OF MOTOR UNIT RECRUITMENT THRESHOLD VERSUS MEAN FIRING RATE RELATIONSHIPS DURING SUBMAXIMAL CONTRACTIONS," International Journal of Exercise Science: Conference Proceedings: Vol. 11: Iss. 2, Article 39.
Available at: https://digitalcommons.wku.edu/ijesab/vol11/iss2/39