Abstract
Purpose
To examine differences in the electromyographic vs torque (EMG-T) relationship, as well as muscle strength and indicators of muscle mass and quality between young versus postmenopausal females, and explore whether the potential differences in the EMG-T relationships could be explained by differences in muscle mass.
Methods
Thirty young (age = 20.7 ± 2.8 y) and 30 postmenopausal (age = 56.3 ± 4.7 y) females completed maximal isometric strength testing (MVIT) and isometric ramp contractions at 40% and 70% MVIT, during which electromyographic signals were collected to quantify the slopes (Slope40; Slope70) and intercepts (Intercept40; Intercept70) of the EMG-T relationships. Muscle mass and quality measurements were also completed.
Results
Postmenopausal females exhibited lower skeletal muscle mass (− 2.3 ± 1.5 kg), fat-free mass index (− 1.1 ± 0.7 kg·m−2), MVIT (− 17.1 ± 16.3 Nm), phase angle (− 0.5 ± 0.0°), muscle cross-sectional area (− 5.5 ± 1.1 cm2), muscle quality (− 0.1 ± 0.0 a.u), Slope40 (− 0.0003 ± 0.0002 mV·%MVIT−1), Slope70 (− 0.0003 ± 0.0002 mV·%MVIT−1), and had a higher echo intensity (+ 9.8 ± 2.8 a.u), Intercept40 (+ 0.001 ± 0.001 mV), and Intercept70 (+ 0.004 ± 0.003 mV) (p ≤ 0.001–0.04) than the young females. The EMG-T relationship variables were correlated with both muscle mass and quality after controlling for bodyweight. When controlling for muscle mass and bodyweight, group differences in the slopes of the EMG-T relationship and muscle strength were eliminated.
Conclusion
Muscle mass and quality are primary contributors to the decrements in neuromuscular function observed in postmenopausal versus young females, and the preservation of muscle mass should be prioritized in the years leading up to, during, and immediately after menopause.
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Data availability
Data will be made available upon reasonable request.
Abbreviations
- ANCOVA:
-
Analysis of Covariance
- BIA:
-
Bioelectrical impedance analysis
- EI:
-
Echo intensity
- EMG:
-
Electromyography
- EMG-T:
-
Electromyographic vs. Torque
- FFMI:
-
Fat-free mass index
- Intercept40, Intercept70 :
-
Intercept at 40%/70% maximal voluntary isometric torque
- MVIC:
-
Maximal voluntary isometric contraction
- MVIT:
-
Maximal voluntary isometric torque
- MU:
-
Motor Unit
- MUAP:
-
Motor Unit Action Potential Amplitude
- Mcsa:
-
Muscle cross-sectional area
- MQ:
-
Muscle quality
- PA:
-
Phase angle
- SMM:
-
Skeletal muscle mass
- Slope40, Slope70 :
-
Slope at 40%/70% maximal voluntary isometric torque
- sEMG:
-
Surface electromyography
- US:
-
Ultrasound
- VL:
-
Vastus lateralis
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Acknowledgments
Thank you to all of the participants of this study for volunteering their time and effort. Thank you to Tyler W.D. Muddle, Ryan J. Colquhoun, and Patrick M. Tomko for your roles in data collection. The data included in this manuscript include those collected during projects supported by the Center for Integrative Research on Childhood Adversity (Award Number P20GM109097) and the American Heart Association (Award Number: 18AIREA33960528).
Funding
The data included in this manuscript include those collected during projects supported by the Center for Integrative Research on Childhood Adversity under Award Number P20GM109097 and the American Heart Association (Award Number: 18AIREA33960528).
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N.F.B. carried out data analysis and interpretation, and was the primary author. E.M.R. helped carry out data acquisition and interpretation. N.F.B. and N.D.M.J. created figures and tables. N.D.M.J. was the primary manuscript reviser and a substantial contributor to study concept, study design, and interpretation. All authors read, revised, and approved the final version of this manuscript. All authors agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
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This study was approved by and conducted in accordance with the guidelines and regulations of the Oklahoma State University’s Institutional Review Board (IRB Approval #s: ED-17-157 and ED-18-101) and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
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Banks, N.F., Rogers, E.M. & Jenkins, N.D.M. Electromyographic amplitude versus torque relationships are different in young versus postmenopausal females and are related to muscle mass after controlling for bodyweight. Eur J Appl Physiol 121, 479–488 (2021). https://doi.org/10.1007/s00421-020-04532-0
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DOI: https://doi.org/10.1007/s00421-020-04532-0