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

• Published in: Journal of applied physiology (1985) 2004-01, Vol.96 (1), p.211-217
• Main Authors: Medved, Ivan, Brown, Malcolm J, Bjorksten, Andrew R, McKenna, Michael J
• Format: Article
• Language: English
• Subjects: Acetylcysteine - administration & dosage; Acetylcysteine - adverse effects; Adult; Antioxidants; Bicycling; Bicycling - physiology; Biological and medical sciences; Blood; Cross-Over Studies; Double-Blind Method; Exercise; Fatigue; Free Radical Scavengers - administration & dosage; Free Radical Scavengers - adverse effects; Fundamental and applied biological sciences. Psychology; Humans; Infusions, Intravenous; Male; Muscle Fatigue - drug effects; Muscle Fatigue - physiology; Muscle, Skeletal - metabolism; Muscle, Skeletal - physiology; Muscular system; Oxygen Consumption - drug effects; Oxygen Consumption - physiology; Physical Exertion - drug effects; Physical Exertion - physiology; Potassium - blood; Reactive Oxygen Species - metabolism
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00458.2003

1 Muscle, Ions and Exercise Group, School of Human Movement, Recreation and Performance, Centre for Rehabilitation, Exercise and Sport Science, Victoria University of Technology, Melbourne 8001; 2 Department of Anaesthesia, Austin and Repatriation Medical Centre, Melbourne 3084; and 3 Department of Anaesthesia and Pain Management, Royal Melbourne Hospital, Melbourne, Victoria 3052, Australia Submitted 2 May 2003 ; accepted in final form 29 August 2003 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 men completed a double-blind, crossover study, receiving NAC or placebo before and during cycling exercise, comprising 45 min at 70% of peak oxygen consumption ( O 2 peak ) and then to fatigue at 90% O 2 peak . NAC was intravenously infused at 125 mg·kg -1 ·h -1 for 15 min and then 25 mg·kg -1 ·h -1 for 20 min before 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, or plasma electrolytes. Time to fatigue was reproducible in preliminary trials (coefficient of variation 7.4 ± 1.2%) and was not augmented by NAC (NAC 14.6 ± 4.5 min; control 12.8 ± 5.4 min). However, time to fatigue during NAC trials was correlated with O 2 peak ( r = 0.78; P < 0.05), suggesting that NAC effects on performance may be dependent on training status. The rise in plasma K + concentration at fatigue was attenuated by NAC ( P < 0.05). The ratio of rise in K + concentration to work and the 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. reactive oxygen species; muscle fatigue; sodium-potassium-adenosine triphosphatase; training status Address for reprint requests and other correspondence: M. J. McKenna, School of Human Movement, Recreation and Performance (FO22), Victoria Univ. of Technology, PO Box 14428, MCMC, Melbourne, Victoria, Australia, 8001 (E-mail: michael.mckenna{at}vu.edu.au ).