NAC Improves Markers of Oxidative Stress Induced by High Intensity Exercise

The word "anti-oxidant" has lost some of its glory within the past couple of years. In absence of overt deficiency, the real-world effects of super high doses of vitamins and other nutrients which have been found to exhibit anti-oxidant activities is negligible if not opposing to the originally intended effect. One of those anti-oxidants which may even produce adverse side effects at very high doses is N-acetyl-cysteine (NAC).
For athletes who expose their bodies to a high amount of oxidative damage, NAC may yet well be a candidate for the list of basic supplements you may want to consider to take. A recent study (Trevin. 2010) involving nine well-trained male cyclists (mean ± SD; 27 ± 6 years of age, VO2peak 69.4 ± 5.8 ml.kg−1.min−1) found that a NAC-loading protocoll consisting of 2 days on 100mg/kg NAC, followed by one day with two servings of 100mg/kg and another dose of 100mg/kg 1h before a 10 minute self-paced time trial, produced the following results:

Respiratory Exchange Ratio (RER) was decreased in the NAC condition throughout HIT exercise, and was significant at bouts 1 and 5 (p < 0.05) as shown in The Figure. Compared to placebo, NAC decreased blood lactate during TT and recovery (p < 0.05). Both pH (p < 0.01), and HCO3 (p <0.05) were reduced throughout exercise and recovery with NAC. In contrast NAC resulted in higher blood glucose concentration during HIT (p < 0.05). EMG median frequency of the vastus lateralis decreased in HIT bout 6 in the NAC condition (p < 0.05). No significant difference was observed in the total work performed in the 10-min TT (p = 0.16) .

So, while it had no direct effect on exercise performance, NAC did increase several performance and recovery related parameters and probably shifted the substrate metabolism from carbs to fats, thus leaving the athletes with a higher blood glucose concentration during and after their high intensity interval sessions.