Competitive swimming is a highly researched area and technological developments have aided advances in the understanding of the biomechanical principles that underpin these elements and govern propulsion. Moreover, those working in the sports field especially in swimming are interested in studying, analyzing, evaluating and developing motor skills by diagnosing the strengths and weaknesses of the skill, and accordingly, coaches and specialists correct these errors. The researchers chose this (Butterfly swimming) and the (arm length) is an important variable because the success of the stroke is greatly dependent on the propulsion generated from the arm pull, and swimmers with a longer arm span have a mechanical advantage with the resulting force being greater than those with a shorter arm span are. The descriptive method was used in a comparative manner, and the research sample was chosen intentionally are (3) swimmers from the advanced category in the (50 m) The Second International Scientific Conference of the Arab Society for Biomechanics in Sports butterfly swimming. This study took one month to filming the swimmers and take (8) kinematic variables were determined, it was identified that there is a significant relationship between the following variables (maximum time for strike, maximum time for arm (recovery phase), total of arm strikes and rate length for Strike). Moreover, the conclusion was Based on the presented data, butterfly swimming performance was depend on (upper limps) in general, the (Arm length) in particular, and more on technical variables (mainly motor coordination .)
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