What type of speed would a 400m runner predominantly rely on?

In the context of a 400m race, a runner predominantly relies on speed endurance. This type of speed refers to the ability to maintain a high speed over a longer distance while resisting fatigue. The 400m event, being a race that combines both sprinting and endurance elements, requires athletes to sustain a significant pace throughout the race's full distance.

Speed endurance training focuses on enhancing the muscle's ability to work efficiently under conditions where fatigue would typically set in. This allows the athlete to perform at a high intensity, ensuring they maintain their speed as they approach the latter stages of the race.

While acceleration speed is important for the initial phase of the race, and pure speed would be relevant for shorter sprints, the unique demands of the 400m event make speed endurance the critical factor for success. Reaction speed, although useful at the start, is less significant in the overall performance of a 400m runner compared to the need to sustain speed throughout the distance.