With the recent push for increased physical activity, participation in triathlons has dramatically increased. Triathlons consist of a three-sport endurance event consisting of swimming, cycling and running. Many people who participate in these events come from a strong background in one of the sports and then train for the other two legs. A recent study demonstrated that the risk of sudden death in the triathlon was 1.5 per 100,000 participants. The study included 922,810 participants. There were a total of 14 deaths, 11 in men and 3 in women. Thirteen of the deaths occurred during the swimming leg of the race and were initially thought to be from drowning. Autopsies were performed on 6 of the 13 swimming deaths and underlying cardiovascular disease was found in 4 of them. Some possible reasons for the swim being the most dangerous leg included: cold water causing irregular heart rhythms, the inability for the athlete to stop and rest when he/she is in trouble and just inexperience in the water. The different triathlon distances did not have an effect on the death rates. In comparison, a study of 3 million marathon runners showed the sudden cardiac death rate to be 0.8 per 100,000 participants (almost ½ of the triathlon rate).