Start Depth Modification by Adolescent Competitive Swimmers

To expand upon previous studies showing inexperienced high school swimmers can complete significantly shallower racing starts when asked to start “shallow,” 42 age group swimmers (6-14 years old) were filmed underwater during completion of competitive starts. Two starts (one normal and one “requested shallow”) were executed from a 0.76 m block into 1.83 m of water. Dependent measures were maximum depth of the center of the head, head speed at maximum head depth, and distance from the starting wall at maximum head depth. Statistical analyses yielded significant main effects (p < 0.05) for start type and age. The oldest swimmers’ starts were deeper and faster than the youngest swimmers’ starts. When asked to start shallowly, maximum head depth decreased (0.10 m) and head speed increased (0.32 ms-1) regardless of age group. The ability of all age groups to modify start depth implies that spinal cord injuries during competitive swimming starts are not necessarily due to age-related deficits in basic motor skills. The safety risks associated with the execution of a competitive racing start are due to several factors. Some of these are under the swimmer’s control and some are not. For example, the trajectory of the body upon leaving the starting block, the velocity at which the body is traveling, and the depth of the head during the trajectory are to a large extent determined by the swimmer or the physical body characteristics such as mass and strength. Block height and water depth, in contrast, are a function of the facility and regulatory requirements. If a swimmer comes into contact with the pool bottom, the severity of the injury that occurs is influenced by the swimmer’s momentum, primarily a function of the velocity and mass of the swimmer. The swimmer’s velocity is related to the forces generated by the swimmer while on the block, the swimmer’s ability to reduce the resistive forces (streamline) once entering the water, and the height of the block above the water surface. The execution of a safe racing start therefore requires the swimmer to exhibit a complex blend of motor abilities, including such skills as static and dynamic balance, multiple axial movements, and ballistic locomotor skills.