Skip to main content

Motor unit action potential amplitude during low torque fatiguing contractions versus high torque non-fatiguing contractions: a multilevel analysis

Abstract

Purpose

The ability to maintain an absolute, submaximal torque level during fatiguing contractions is controlled, in part, by the recruitment of larger motor units. These motor units are commonly identified based on greater action potential peak-to-peak amplitude values. It is unclear, however, if motor unit action potential (MUAP) amplitude values during low torque, fatiguing contractions reach similar levels as those observed during non-fatigued, high torque contractions. To establish a clearer understanding of motor unit control during fatigue, we compared MUAP amplitude during 50 and 80% maximum voluntary contraction (MVC) torque contractions and at the beginning, middle, and end of a 30% MVC fatigue protocol.

Methods

Eleven untrained men (mean age = 24 years) performed isometric contractions at 50 and 80% MVC, followed by repeated contractions at 30% MVC. Surface electromyographic (EMG) signals were detected from the vastus lateralis and decomposed to quantify the peak-to-peak amplitude of individual MUAPs. A two-level multilevel model was estimated, allowing examination of simultaneous measures of MUAP amplitude within participants and controlling for the dependence between measures within participants.

Results

Results from the multilevel analyses suggested that there were not statistically significant differences in MUAP amplitude between 80% MVC and end fatigue. Separate repeated-measures analyses of variance indicated that there were not statistically significant mean differences in greatest MUAP or surface EMG amplitude between 80% MVC and end fatigue.

Conclusions

MUAP and surface EMG amplitude values during a 30% MVC fatiguing protocol appear to be comparable to those observed during a non-fatigued 80% MVC condition.

This is a preview of subscription content, access via your institution.

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5

Data availability

All data analyzed during this study are included in supplementary information files.

Abbreviations

ANOVA:

Analysis of variance

EMG:

Electromyography

MUAP:

Motor unit action potential

MVC:

Maximum voluntary contraction

References

Download references

Funding

No funding was provided for this study.

Author information

Authors and Affiliations

Authors

Contributions

This study was conceived of and designed by MS. Data collection was performed by all authors, except for DHV. DHV conducted the statistical analyses and provided feedback concerning data interpretation. The first draft of the manuscript was written by KH. All authors provided edits and feedback in preparation for manuscript submission. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Matt S. Stock.

Ethics declarations

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

All procedures performed involving human participants were in accordance with the ethical standards of the Institutional Review Board and with the 1964 Helsinki Declaration and its later amendments. The study was approved by the Institutional Review Board of The University of Central Florida (BIO-17-12855).

Informed consent to participate

Informed consent was obtained from all individual participants included in the study.

Additional information

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Communicated by William J. Kraemer.

Supplementary Information

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Harmon, K.K., Hamilton, A.S., Johnson, B.D. et al. Motor unit action potential amplitude during low torque fatiguing contractions versus high torque non-fatiguing contractions: a multilevel analysis. Eur J Appl Physiol 121, 1145–1157 (2021). https://doi.org/10.1007/s00421-021-04606-7

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1007/s00421-021-04606-7

Keywords

  • Motor unit recruitment
  • Surface EMG
  • Fatigue
  • Motor unit size