In butterfly, which attribute is essential for propulsion?

• A. Arm strength and body undulation
• B. Slow breathing only
• C. Minimal hip movement
• D. None required; it's a passive stroke

Answer: (A)

Propulsion in butterfly comes from a coordinated action: a strong arm pull paired with continuous body undulation driven by the hips and core. The arms generate forward thrust during the catch and pull, pushing water backward as they sweep, while the torso undulates in a dolphin-like wave that transfers energy from the hips through the spine to the hands and water. This undulation amplifies the force of the arm drive and helps sustain speed between strokes. Breathing affects rhythm and oxygen but won’t create forward propulsion by itself. If hip movement is minimized, the undulation loses power and propulsion drops. This is an active stroke where propulsion comes from the combination of arm work, body wave, and the kick, not from passive movement.