Motor unit firing rates of the first dorsal interosseous differ between male and female children aged 8-10 years

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

doi:10.1016/j.humov.2019.04.011

Motor unit firing rates of the first dorsal interosseous differ between male and female children aged 8-10 years

Hum Mov Sci. 2019 Aug:66:416-424. doi: 10.1016/j.humov.2019.04.011. Epub 2019 Jun 4.

Authors

Trent J Herda¹, Jonathan D Miller², Mandy E Wray², Adam J Sterczala³, Hannah L Dimmick², Michael A Trevino⁴

Affiliations

¹ Neuromechanics Laboratory, University of Kansas, Lawrence, KS, United States. Electronic address: t.herda@KU.edu.
² Neuromechanics Laboratory, University of Kansas, Lawrence, KS, United States.
³ Neuromuscular Research Laboratory, University of Pittsburg, Pittsburg, PA, United States.
⁴ Applied Neuromuscular Physiology Laboratory, Oklahoma State University, Stillwater, OK, United States.

PMID: 31174016
DOI: 10.1016/j.humov.2019.04.011

Abstract

The purpose of this study was to examine possible differences in motor unit action potential amplitudes (MUAP_AMPS) and firing rates of the first dorsal interosseous (FDI) in male and female children aged 8-10 years. Eight male (mean ± SD, age = 8.8 ± 0.7 yrs; BMI = 16.5 ± 1.3 kg/m²) and eight female (age = 9.3 ± 0.9 yrs; BMI = 16.1 ± 1.5 kg/m²) children volunteered to complete isometric trapezoidal muscle actions of the first dorsal interosseous at 50% of maximal voluntary contraction (MVC). Electromyographic signals were decomposed to yield MUAP_AMPS and mean firing rates (MFR) at the targeted force. An exponential model was fitted to the MUAP_AMPS vs. recruitment threshold (RT) while linear models were fitted to the MFRs vs. RT relationships for each subject. Ultrasonography determined the muscle cross-sectional area (CSA) of the FDI. Independent samples t-tests were used to examine possible differences between the male and female children for MVC strength, CSA, and the coefficients from the MU relationships. There were no differences in MVC strength, CSA, or the MUAP_AMP vs. RT relationships between the male and female children (P < 0.05). Males, however, had greater MFRs of lower-threshold MUs as evident by significantly larger y-intercepts (P = 0.019) and more negative slopes (P = 0.004) from the MFR vs. RT relationships. Despite no differences in muscle strength, CSA, and MUAP_AMPS, differences in firing rates existed between male and female children aged 8-10 years. Neural mechanisms may primarily contribute to sex-related differences in firing rates.

Keywords: Children; Firing rates; First dorsal interosseous; Motor units.