What is the focus of the fourth progression in backstroke?

Focusing on the fourth progression in backstroke, the emphasis is on performing the stroke over a distance of 15 yards with the technique of windmill arms. This particular progression helps swimmers to solidify their coordination and body position while enhancing the efficiency of their strokes. The windmill arm action is crucial in backstroke as it promotes a continuous, rhythmic movement that is essential for maintaining momentum and balance in the water.

Swimmers are encouraged to concentrate on a smooth recovery phase and effective arm entry, which are critical components of the backstroke technique. By practicing over this specific distance, swimmers can build endurance and confidence, allowing them to transition effectively to longer distances later on, which could be represented by options that suggest 25 yards or more.

The other choices represent distances that may either be too short or suggest different specific activities that do not focus on the windmill arm technique, which is vital in the fourth progression for promoting a deeper understanding and execution of backstroke swimming. This progression represents an essential step in developing backstroke skills through distance and technique focus, preparing swimmers for more advanced levels.