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J Appl Physiol (September 5, 2003). doi:10.1152/japplphysiol.00458.2003
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Submitted on May 2, 2003
Accepted on August 29, 2003

Effects of intravenous N-acetylcysteine infusion on time to fatigue and potassium regulation during prolonged exercise

Ivan Medved1, Malcolm J Brown2, Andrew R Bjorksten3, and Michael J McKenna1*

1 Muscle, Ions and Exercise Group; School of Human Movement, Recreation & Performance; Centre for Rehabilitation, Exercise and Sport Science, Victoria University of Technology, Melbourne, Victoria, Australia
2 Anaesthesia, Austin and Repatriation Medical Centre, Melbourne, Victoria, Australia
3 Anaesthesia and Pain Management, Royal Melbourne Hospital, Melbourne, Victoria, Australia

* To whom correspondence should be addressed. E-mail: michael.mckenna{at}vu.edu.au.

The production of reactive oxygen species in skeletal muscle is linked with muscle fatigue. This study investigated whether the antioxidant compound N-acetylcysteine (NAC) augments time to fatigue during prolonged, submaximal cycling exercise. Seven males completed a double-blind, crossover study, receiving NAC or placebo before and during cycling exercise, comprising 45 min at 70%VO2peak, then to fatigue at 90%VO2peak. NAC was intravenously infused at 125 mg.kg-1.hr-1 for 15 min, then 25 mg.kg-1.hr-1 for 20 min prior to and throughout exercise, which was continued until fatigue. Arterialized venous blood was analyzed for NAC concentration, hematology and plasma electrolytes. NAC induced no serious adverse reactions and did not affect hematology, acid-base status and plasma electrolytes. Time to fatigue was reproducible in preliminary trials (CV 7.4±1.2%) and was not augmented by NAC (NAC 14.6±4.5 min; CON 12.8±5.4 min). However, time to fatigue during NAC trials was correlated with VO2peak (r=0.78; P<0.05), suggesting that NAC effects on performance may be dependent on training status. The rise in plasma [K+] at fatigue was attenuated by NAC. The {Delta}[K+].work-1 ratio and percentage change in time to fatigue tended to be inversely related (r=-0.71; P<0.07). Further research is required to clarify a possible training status-dependent effect of NAC on muscle performance and K+ regulation.




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