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The objectives of this study were to develop an improved method of measuring kinematic parameters of a swimmer at the start of a race from water entry through the initial glide in a seamless manner and to consider deceleration factors with reference to changes in the swimmer’s kinematic parameters during the start. Ten elite collegiate male swimmers participated in this study. To obtain accurate displacements of each reference point on a swimmer while avoiding interference from bubbles, waterproofed, super-luminosity LED markers were used. Additionally, a metallic frame (3 m × 2 m) and a nylon belt (6.1 m long with marks at intervals of 0.5 m) were used as calibration control points. Participants were asked to start from a starting block three times with their maximum effort and maintain a streamlined position without any kicking after water entry until they reached the 10-m point. The mean calibration error was 0.0046 m in the horizontal direction and 0.0047 m in the vertical direction across the measurement span (11 m × 6 m). This improved method enabled us to measure successive changes in the velocity and acceleration of the centre of mass both above water and following water entry.