[Effect of change of plasma K+ and pH value induced by exercise on muscle fatigue and surface EMG]
Related Experiment Video
Updated: Feb 10, 2026

Muscle Function Obtained with Motion Mode Ultrasound and Surface Electromyography during Core Endurance Exercise
Published on: August 25, 2022
Wei He1, Mian-zhen Wang, Zhi-ming Wang
1Department of Occupational Health, West China School of Public Health, Sichuan University, Chengdu 610041, China.
Objective:
This study was undertaken to explore the relationship between plasma K+, H+ and muscle fatigue as well as electromyogram changes.
Methods:
Fourteen male students enrolled as the subjects of this study performed two exercise tests of different intensity (200 W; 120 W) on a cycle ergometer till being fatigued. The plasma K+, pH value and electromyography (EMG) of active and inactive muscles during 10 s isometric contraction fixed load were measured before exercise and at 0, 5, 10, 20 minutes after exercise.
Results:
Both plasma K+ and mean power frequency (MPF) of the active muscles changed significantly (P<0.01) after exercise, but recovered in 20 minutes and were highly negatively correlated. Plasma pH at 20 minutes after 200 W exercise was significantly lower than that at rest (P<0.01), but did not change after 120 W exercise, and no correlation was found between pH and EMG. Integral electromyography (IEMG) of inactive muscles at 20 minutes after 120 W exercise was significantly lower than that at rest (P<0.05).
Conclusion:
The results showed that high extra cellular K+ concentration for exercise is one of the main factors inducing fatigue and MPF decrease of the active muscles as well as IEMG decrease of the inactive muscle, but H+ is not a main factor for fatigue and it has no direct effect on EMG.
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