The most significant portion is the primary portion of swimming, cycling, or running. It is designed to provide the entire body with exercise. It tends to follow the warm-up and precede the cool-down.
The main set, and one that may incorporate threshold intervals, tempo attempts, or VO2 max sets, is that which targets the improvements you seek on race day, such as increasing endurance, speed, or fitness. A good example of a main set is 10 x 100 meters at race pace in swimming. A main set maximizes how you spend training time because you are targeting specific gains.
