A key factor in Viagra is its ability to increase blood flow. Its active ingredient, sildenafil citrate, cause the blood vessels to relax, which improves blood flow from the heart and increases oxygen to the muscles. Studies conducted two years ago on a group of elite cyclists showed that Viagra taken at altitude produced a marked improvement - up to 15 per cent faster time trials - by 45 per cent of those who took the drug. But at sea level the drug shows no benefit. Still, athletes desperate to find the smallest advantage, don’t take notice of the fine print.
