File
K. Kawamura1, S. Iida1, M. Kobayashi2, Y. Setaka1, K. Tomita1,2
1Ibaraki Prefectural University of Health Sciences, Department of Physical Therapy, Ami-machi, Japan, 2Ibaraki Prefectural University of Health Sciences, Graduate School of Health Sciences, Ami-machi, Japan
Background: Muscle electromyography in the lower limb increases during incremental exercise test, which also involves the break points (EMG threshold; EMGth). EMGth reportedly increased firing frequency of motor units, mainly type II fibers, and pH reduction, which correlates with anaerobic threshold (AT). However, EMGth in respiratory muscles is still unknown. It is important to clarify changes in respiratory muscle activity during exercise because respiratory muscle fatigue is a limiting factor in exercise.
Purpose: The purpose of this study was to examine changes in respiratory muscles activity during incremental exercise and determine the relationship between EMGth and AT.
Methods: Fourteen healthy men, who were non-smokers and did not engage in regular heavy exercise, were recruited. Participants were aged 22.0 years (21.0-23.5 years) (median (25%-75%)), 1.72 m (1.69-1.77 m) in height, and 65.2 kg (60.8-70.0 kg) in weight. Their BMI was 21.9 kg/m2 (21.0-23.4 kg/m2). An incremental exercise test was performed on a cycle ergometer. At the beginning of the test, the participants took rest for a minute, which was followed by three minutes of warm up pedaling at 20 watts. Then, the workload was increased by 15 watts every minute till endpoint. The criteria for endpoint of the exercise test were inability to continue exercising due to symptomatic limitations or when participant’s heart rate exceeded 80% of maximum predicted heart rate. For all participants, oxygen uptake (VO2) and carbon dioxide output (VCO2) were recorded by a gas analyzer. The electromyograms of the sternocleidomastoid, parasternal intercostal muscle, diaphragm, rectus abdominis, rectus femoris, vastus lateralis and lateral head of gastrocnemius were recorded at rest and during exercise. The EMG data converted to RMS were averaged for every respiratory phase. EMGth was analyzed using the segmented regression model. Correlation between EMGth and AT was analyzed using Spearman rank correlation method.
Results: The maximum work rate of the exercise test was 170.5 watts (155.5-198.3 watts) and peak VO2 was 24.9 ml/min/kg (23.9-30.7 ml/min/kg). AT was identified in all participants at 65.0 watts (57.0-79.3 watts) and VO2 of 10.2 ml/min/kg (8.4-10.8 ml/min/kg). The work rates at AT and sternocleidomastoid, rectus femoris, and vastus lateralis muscle were significantly correlated.
Conclusion(s): EMGth of the sternocleidomastoid and the work rate at AT were found to be correlated.
Implications: Patients with respiratory and cardiovascular diseases have more effortful respiratory muscle activity than healthy individuals, which can be a limiting factor for exercise. A more accurate assessment of respiratory muscle activity during exercise would be useful in prescribing exercise for patients with respiratory and cardiovascular diseases.
Funding, acknowledgements: This study received no funding.
Keywords: Electromyography, Anaerobic threshold, Respiratory muscles
Topic: Cardiorespiratory
Did this work require ethics approval? Yes
Institution: Ibaraki Prefectural University of Health Sciences
Committee: Ethics Committee at the Ibaraki Prefectural University
Ethics number: Approval number 950
All authors, affiliations and abstracts have been published as submitted.
