Creatine is thought to improve strength, increase lean muscle mass, and help the muscles recover more quickly during exercise . This muscular boost may help athletes achieve bursts of speed and energy, especially during short bouts of high-intensity activities such as weight lifting or sprinting. However, scientific research on creatine has been mixed. Although some studies have found that it does help improve performance during short periods of athletic activity, there is no evidence that creatine helps with endurance sports. Research also shows that not everyone's muscles respond to creatine; some people who use it see no benefit.
Because of an editing error, an article on Monday about teenage boys and body image misstated the number of boys who were interviewed as part of a recently published survey. It was 1,307, not 2,800. The article also misidentified the academic affiliation of a doctor who commented on supplements and steroids. The doctor, Shalender Bhasin, is a professor of medicine at Boston University School of Medicine and chief of endocrinology, diabetes and nutrition at Boston Medical Center. He is not a professor at Boston Medical Center. And the article misidentified the nationality of the soccer player Cristiano Ronaldo, whose body a teenager quoted in the article said he would like to emulate. Mr. Ronaldo is Portuguese, not Brazilian.