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European Journal of Applied Physiology

, Volume 119, Issue 9, pp 1971–1979 | Cite as

Isometric-based test improves EMG-threshold determination in boys vs. men

  • Stacey Woods
  • Raffy Dotan
  • Nicole Jenicek
  • James Maynard
  • David Gabriel
  • Craig Tokuno
  • Bareket FalkEmail author
Original Article

Abstract

Background

Children have been hypothesized to utilize higher-threshold (type-II) motor units (MUs) to a lesser extent than adults. Two recent studies, using a cycling-based EMG-threshold (EMGTh) protocol, supported the hypothesis, showing children’s EMGTh intensities to be higher than adults’. Conclusions, however, were hampered by children’s low EMGTh detection rates. Insufficiently high contractile forces at exhaustion were postulated as the reason for non-detection, predominantly in children. An intermittent isometric contraction test (IICT) protocol facilitates higher contractile forces prior to exhaustion and was shown effective in EMGTh testing of adults.

Purpose

Determine whether an IICT protocol would enhance EMGTh detection in children, and consequently increase the magnitude of the previously observed child–adult EMGTh differences.

Methods

18 boys and 21 men completed one-repetition-maximum (1RM) isometric knee-extension test. The IICT protocol followed, commencing at 25%1RM and comprising five isometric contractions per load, incremented by ~ 3%1RM to exhaustion. Vastus lateralis surface EMG was recorded and EMGTh, expressed as %1RM, was defined as the onset of the EMG-response’s steeper segment.

Results

EMGTh was detected in 88.9% of boys and 95.2% of men, and occurred at higher relative intensities in boys (56.4 ± 9.2%1RM) than in men (46.0 ± 6.8%1RM). This 10.4% difference was 57% greater than the corresponding, previously reported cycling-based age-related difference.

Conclusions

With the boys’ detection rate nearly on par with the men’s, the IICT protocol appears to overcome much of the intensity limitation of cycling-based protocols and provide a more sensitive EMGTh detection tool, thus extending the previously observed boys‒men difference. This difference adds supports to the notion of children’s more limited type-II MU recruitment capacity.

Keywords

Child Exercise Fatigue Force Electromyography Maturation Muscle Neuromotor Torque 

Abbreviations

EMG

Electromyography

EMGTh

Electromyographic threshold

EMGRMS

Root mean square of each contraction’s EMG signal

EMGRMS5

Average of EMGRMS values for each load

IICT

Intermittent isometric contraction test

LBM

Lean body mass

LSS

Least sum of squares

MU

Motor units

MVC

Maximal volitional contraction

RM

Repetition maximum

RMS

Root mean square

Notes

Acknowledgements

The authors wish to thank all participants for their hard work and dedication and to the parents or guardians for bringing the boys and making it all possible.

Author contributions

SW, RD and BF conceived and designed research. SW, NJ, RD and JM conducted the experiments. RD designed and built the custom-made ergometer. SW and RD analyzed the data. SW, RD and BF wrote the manuscript. DG and CT contributed to the design of the experiments and the analysis approach. All the authors read and approved the manuscript.

Funding

The study was funded by a Brock University internal grant.

Compliance with ethical standards

Conflict of interest

The authors have no competing interests to declare.

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Department of Kinesiology, Faculty of Applied Health SciencesBrock UniversitySt. CatharinesCanada
  2. 2.Faculty of Applied Health SciencesBrock UniversitySt. CatharinesCanada
  3. 3.Centre for Bone and Muscle Health, Faculty of Applied Health SciencesBrock UniversitySt. CatharinesCanada

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