Abstract
N‐acetylcysteine (NAC; antioxidant and thiol donor) supplementation has improved exercise performance and delayed fatigue, but the underlying mechanisms are unknown. One possibility is NAC supplementation increases limb blood flow during severe‐intensity exercise. The purpose was to determine if NAC supplementation affected exercising arm blood flow and muscle oxygenation characteristics. We hypothesized that NAC would lead to higher limb blood flow and lower muscle deoxygenation characteristics during severe‐intensity exercise. Eight healthy nonendurance trained men (21.8 ± 1.2 years) were recruited and completed two constant power handgrip exercise tests at 80% peak power until exhaustion. Subjects orally consumed either placebo (PLA) or NAC (70 mg/kg) 60 min prior to handgrip exercise. Immediately prior to exercise, venous blood samples were collected for determination of plasma redox balance. Brachial artery blood flow (BABF) was measured via Doppler ultrasound and flexor digitorum superficialis oxygenation characteristics were measured via near‐infrared spectroscopy. Following NAC supplementaiton, plasma cysteine (NAC: 47.2 ± 20.3 μmol/L vs. PLA: 9.6 ± 1.2 μmol/L; P = 0.001) and total cysteine (NAC: 156.2 ± 33.9 μmol/L vs. PLA: 132.2 ± 16.3 μmol/L; P = 0.048) increased. Time to exhaustion was not significantly different (P = 0.55) between NAC (473.0 ± 62.1 sec) and PLA (438.7 ± 58.1 sec). Resting BABF was not different (P = 0.79) with NAC (99.3 ± 31.1 mL/min) and PLA (108.3 ± 46.0 mL/min). BABF was not different (P = 0.42) during exercise or at end‐exercise (NAC: 413 ± 109 mL/min; PLA: 445 ± 147 mL/min). Deoxy‐[hemoglobin+myoglobin] and total‐[hemoglobin+myoglobin] were not significantly different (P = 0.73 and P = 0.54, respectively) at rest or during exercise between conditions. We conclude that acute NAC supplementation does not alter oxygen delivery during exercise in men.
Highlights
The production of free radicals occurs at rest (Richardson et al 2007; Bailey et al 2007) and increases during exercise (Richardson et al 2007; Bailey et al 2003, 2004, 2007)
Following N -acetylcysteine (NAC) supplementation, the increased CySH, GSSG, and CySH:Total cysteine (tCyS) occurred in all eight subjects, while the increases in tCyS and tGSH occurred in six of eight subjects
The major findings of this study are that an acute oral supplementation of NAC does not affect blood flow or muscle oxygenation characteristics at rest or during severe-intensity handgrip exercise in healthy men
Summary
The production of free radicals occurs at rest (Richardson et al 2007; Bailey et al 2007) and increases during exercise (Richardson et al 2007; Bailey et al 2003, 2004, 2007). Endogenous antioxidant systems (e.g., superoxide dismutase, catalase, glutathione peroxidase) help minimize the increase in free radicals (Sen 1995), the accumulation of free radicals occurs with exercise (Richardson et al 2007; Bailey et al 2003, 2004, 2007), which affects processes associated with muscular fatigue (Reid 2015). In 1990, N -acetylcysteine (NAC), an antioxidant and thiol donor, was shown to delay fatigue in rabbit diaphragm fibers (Shindoh et al 1990). Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society
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