A triathlon is an enurance sports event consisting of swimming, cycling and running over various distances. As a result, proficiency in swimming, cycling, and running alone is not sufficient to guarantee a triathlon athlete a competitive time; trained triathlon athletes have learned to race each stage in a way that preserves their energy and endurance for subsequent stages. In most modern triathlons, these events are placed back-to-back in immediate sequence and a competitor's official time includes the time required to "transition" between the individual legs of the race, including any time necessary for changing clothes and shoes.