Rouard, A. H., & Billat, R. P. (1990). Influences of sex and level of performance on freestyle stroke: an electromyography and kinematic study. International Journal of Sports Medicine, 11, 150-155.

International, national, and regional swimmers (M = 30; F = 20) were electromyographically and cinematographically assessed while swimming repeated 25 m at best-time for 100 m pace.

Full rest occurred between each repetition. The measure of swimming speed was the displacement of the hip while the arm action was divided into five phases relative to the arm-trunk angle: entry of the hand to 45, 45 to 90, 90 to 135, 135 degrees to exit of the hand, and recovery. Each phase was defined as the percentage of total stroke time.

Height, speed of stroke, and swimming speed were closely related. The faster swimmers had lower levels of muscular activity. Females recruited muscle actions in a similar manner to males but had lower performance parameters and therefore, were less efficient. Total time of stroke was not related to performance levels or speed. The best swimmers were more economical in their muscle use and control.

The time phases of the stroke were: entry (35%), 45-90 degrees (9.5%), 90-135 degrees (9.9%), 135 degrees to exit (14.3%), and recovery (31.3%). Swimming with a long arm pull required a greater level of effort in a more consistent fashion across the muscle groups whereas with a bent arm pull, the push was more selective with lower levels of activation (this means that a bent arm pull is more efficient and less exhausting, that is, it is more economical).

At the beginning of the push, water behind a swimmer's upper arm is still. As the push proceeds the mass of the water moves and forms less resistance and less load for the swimmer. Swimmers who push with a long arm have a larger cross-sectional area and, consequently, higher drag. That produces a larger load and requires more muscular effort when compared to what is required when swimming with a bent arm.

Implication. Bending the arm during swimming strokes allows for more force generation, a more horizontal direction of propelling efficiency, and retards fatigue. Attention to this factor in the early phases of all strokes could result in longer and more effective stroking.

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