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Factors contributing to increased muscle fatigue with beta-blockers
R S McKelvie1, N L Jones, G J Heigenhauser
1McMaster University Health Sciences Centre, Hamilton, Ont., Canada.
Canadian Journal of Physiology and Pharmacology
|February 1, 1991
Summary
Beta-blockers impair exercise performance, potentially by affecting muscle ion pumps. This study found that while propranolol increased plasma potassium, this effect did not directly cause reduced exercise capacity at high doses.
Area of Science:
- Exercise Physiology
- Pharmacology
Background:
- Beta-adrenoceptor blockers are common medications with known side effects impacting exercise performance.
- Mechanisms for this impairment include cardiovascular, metabolic, and ion transport effects, specifically inhibition of Na(+)-K+ ATPase pumps.
Purpose of the Study:
- To investigate the relationship between plasma potassium changes and exercise performance impairment in healthy males taking propranolol.
- To determine if elevated plasma potassium levels contribute to reduced exercise capacity during beta-blockade.
Main Methods:
- Healthy male subjects underwent maximal incremental cycle ergometer tests under control, low-dose (LD), and high-dose (HD) propranolol conditions.
- Plasma potassium levels and maximum oxygen uptake were measured.
- High-intensity isokinetic exercise tests were also performed to assess plasma potassium changes and performance.
Main Results:
- Propranolol use resulted in higher plasma potassium levels during exercise compared to control.
- Maximum oxygen uptake was reduced only at the HD of propranolol.
- Despite similar increases in plasma potassium between LD and HD, exercise performance was significantly reduced at HD compared to LD.
Conclusions:
- The observed increases in plasma potassium during propranolol use did not appear to directly cause the reduced exercise performance.
- Other mechanisms likely contribute to exercise impairment associated with beta-blocker therapy.