First, we have to consider the conflicting variables:
Different results in trials using both animals and humans
Varying dosage amounts of nutrients being inconsistent between trial or taken in isolation from other nutrients known to offer benefit and the difference in outcomes; for example, using vitamin C twice a day vs. once per day, in addition to dosing with synthetic Vitamin E vs. natural tocolpherols.
These discrepancies may not be accounted for in the research. In fact, the only factors that were consistent were:
1. The timing of the supplement mattered, and
2. Actual performance was not affected between supplement and non-supplement users.
From a physiology standpoint, that makes a lot of sense. Exercise creates a free radical environment, which relies on the production of free radicals to carry muscles through a catabolic (breakdown) phase, followed by an anabolic (repair or growth) phase.
High dose or combination antioxidants may prevent this necessary action from taking place, thereby making athletic conditioning less efficient at a cellular level. When or if antioxidants are taken during exercise or during a phase of catabolism, presumably, depending on intensity of exercise within two (2) hours post-workout, they may hamper the production of necessary free radicals.
That being said, certain select antioxidants, like alpha-lipoic and R-lipoic acid acid, assist the body in optimal functioning of fatty acid (fuel) utilization for mitochondrial cells found in metabolically-active tissue. So the type of antioxidant matters as much as the timing of the antioxidant.
Recent studies have made the assessment that antioxidants like vitamin C, E and resveratrol may hamper mitochondrial genesis. This in turn makes the muscles less energy efficient in endurance exercise. This was not the case in fast or short burst exercise activity; when there was no presence of the antioxidant, energy metabolism was adequate.
Based on these outcomes and performance of antioxidants for tissue repair (say consumption at night or away from exercise’ catabolic window), antioxidants can be beneficial in the athlete. What we shouldn’t take from the outcome is the assumption that all antioxidants are created equal or perform the same way regardless of our metabolic environment. A prudent recommendation for athletes is to continue to ingest a diet rich in antioxidants, protein and fat in their natural state, while taking select supplements for performance and repair timed appropriate to the body’s metabolic need.