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European Journal of Applied Physiology

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01-04-2019 | Ultrasound | Original Article

Motor unit action potential amplitudes and firing rates during repetitive muscle actions of the first dorsal interosseous in children and adults

Authors: Jonathan D. Miller, Adam J. Sterczala, Michael A. Trevino, Mandy E. Wray, Hannah L. Dimmick, Trent J. Herda

Published in: European Journal of Applied Physiology | Issue 4/2019

Abstract

Purpose

Previous research has indicated greater muscle activation is needed for children (CH) to match relative intensity submaximal contractions in comparison with adults (AD). However, no study has compared motor unit (MU) firing and recruitment patterns between children and adults. Therefore, MU action potential amplitudes (MUAP_AMP) and firing rates were examined during two repetitive submaximal contractions of the first dorsal interosseous in children and adults.

Methods

Twenty-two children (age 9.0 ± 0.8 years) and 13 adults (age 22.9 ± 4.8 years) completed three maximum voluntary contractions (MVC) and two repetitive isometric contractions at 30% MVC for 40 s. Surface electromyography (EMG) was recorded and decomposed into action potential trains. MUAP_AMPS, recruitment thresholds (RTs), and mean firing rates (MFRs) were calculated, and EMG amplitude was normalized (N-EMG) to MVC. For each subject and repetition, linear MFR vs. RT and exponential MUAP_AMP vs. RT and MFR vs. MUAP_AMP relationships were calculated.

Results

N-EMG (P = 0.001, CH = 56.5 ± 31.7%, AD = 30.3 ± 9.1%), MFRs regardless of RT, according to greater y-intercepts of the MFR vs. RT relationships [P = 0.013, CH = 31.1 ± 5.1 pulses per second (pps), AD = 25.9 ± 4.3 pps] and MFRs of MUs with smaller action potential amplitudes (P = 0.017, CH = 29.4 ± 6.8 pps, AD = 23.5 ± 3.5 pps), were greater for children. MUAP_AMPS in relation with RT were similar between groups except the highest threshold MUs (RT = 28% MVC) were greater for the adults (1.02 ± 0.43 mV) than children (0.67 ± 0.24 mV) (P = 0.010).

Conclusions

Muscle activation and MU firing rates were greater for children, which likely indicated a greater operating point of MU control in comparison with adults during an isometric contraction performed at a relative submaximal intensity.

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Title: Motor unit action potential amplitudes and firing rates during repetitive muscle actions of the first dorsal interosseous in children and adults
Authors: Jonathan D. Miller
Adam J. Sterczala
Michael A. Trevino
Mandy E. Wray
Hannah L. Dimmick
Trent J. Herda
Publication date: 01-04-2019
Publisher: Springer Berlin Heidelberg
Keywords: Ultrasound
Electromyographic
Ultrasound
Published in: European Journal of Applied Physiology / Issue 4/2019
Print ISSN: 1439-6319
Electronic ISSN: 1439-6327
DOI: https://doi.org/10.1007/s00421-019-04090-0

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Motor unit action potential amplitudes and firing rates during repetitive muscle actions of the first dorsal interosseous in children and adults

Abstract

Purpose

Methods

Results

Conclusions

Keynote webinar | Spotlight on sleep in brain health

Springer Medicine

Abstract

Purpose

Methods

Results

Conclusions

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