Method of analysis influences interpretations of sex-related differences in firing rates during prolonged submaximal isometric contractions

Hannah L Dimmick; Michael A Trevino; Jonathan D Miller; Mandy E Parra; Adam J Sterczala; Trent J Herda

Method of analysis influences interpretations of sex-related differences in firing rates during prolonged submaximal isometric contractions

J Musculoskelet Neuronal Interact. 2022 Mar 1;22(1):27-36.

Authors

Hannah L Dimmick¹, Michael A Trevino², Jonathan D Miller³, Mandy E Parra⁴, Adam J Sterczala⁵, Trent J Herda³

Affiliations

¹ Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, AB, Canada.
² Applied Neuromuscular Physiology Laboratory Department of Health and Human Performance, Oklahoma State University, Stillwater, OK, USA.
³ Neuromechanics Laboratory, Department of Health, Sport and Exercise Sciences, University of Kansas, Lawrence, KS, USA.
⁴ Mayborn College of Health Sciences, University of Mary Hardin-Baylor, Belton, TX, USA.
⁵ Neuromuscular Research Laboratory, Department of Sports Medicine and Nutrition, University of Pittsburg, Pittsburgh, PA, USA.

PMID: 35234156
PMCID: PMC8919653

Abstract

Objective: This study examined motor unit (MU) firing rates during a prolonged isometric contraction of the vastus lateralis (VL) for females and males.

Methods: Surface electromyographic (sEMG) signals were recorded from the VL for eleven females and twelve males during a 45-second isometric trapezoid muscle actions at 40% of maximal voluntary contraction (MVC). For each MU, mean firing rate (MFR) was calculated for the initial and final 10-second epochs of the steady torque segment and regressed against recruitment threshold (RT, expressed as %MVC), as well as time at recruitment (T_REC, seconds). MFR was also averaged for each subject.

Results: Significant differences existed across epochs for the y-intercepts (P=0.009) of the MFR vs. T_REC relationship, as well as the grouped MFR analysis (P<0.001); no differences were observed between epochs for the MFR vs. RT relationship. Significant differences existed between sexes for the grouped MFR analysis (P=0.049), but no differences were observed for the MFR vs. T_REC or MFR vs. RT relationships.

Conclusion: Analysis method may impact interpretation of firing rate behavior; increases in MU firing rates across a prolonged isometric contraction were observed in the MFR vs. T_REC relationship and the grouped MFR analysis.

Keywords: Electromyography; Motor Unit; Muscle Fatigue; Neuromuscular; Vastus Lateralis.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Action Potentials / physiology
Electromyography
Female
Humans
Isometric Contraction* / physiology
Male
Muscle, Skeletal / physiology
Quadriceps Muscle / physiology
Recruitment, Neurophysiological* / physiology