Some exercisers take vitamin C because they think that it will help them recover faster and therefore become better athletes. However, a study from the University of Valencia in Spain shows that vitamin C pills can make an athlete tire earlier during long-term exercise. ( Journal reference )
Every muscle cell has hundreds, and even thousands, of small inclusions called mitochondria that turn food into the force that drives muscles. They do this by shuffling electrons to produce energy. After the electrons are moved, they can end up stuck on oxygen molecules to produce poisons called oxidants that make muscles burn, and feel sore and tired. The human body produces antioxidants that help protect a person from cell damage from these oxidants. Large doses of vitamin C have been shown to block antioxidants, so giving large doses of vitamin C to either humans and animals before they exercise would make them tire earlier.