The purpose of this study was to examine the changes in velocity and underwater movements during one stroke cycle in competitive breaststroke swimming. The subjects were 19 collegiate swimmers (11 men and 8 women with mean age, 20.9 ± 0.6 y and 20.0 ± 1.0 y; mean height, 173.7 ± 7.0 cm and 165.8 ± 3.8 cm; and mean mass, 66.1 ± 6.7 kg and 59.5 ± 3.9 kg, respectively). They wore a belt that was attached to Speed Meter (manufactured by Vine Inc) via a harness. Each swimmer covered a distance of 25 m twice with the breast-stroke at the highest speed possible. The best time was then analyzed. An underwater video camera (manufactured by YAMAHA K.K) was set up at the center of the pool (at 12.5 m from each end), and it captured pictures of a 5 m section (10 to 15 m). Image analysis revealed 2 acceleration phases in all subjects, which were to the "kick" and "pull" actions of the swimmers. This was agreed upon by the top swimmer of the literature review. Moreover, underwater movement could be estimated from the pattern of change in the speeds on the basis of the relationship between the 2 parameters in the absence of underwater movement.