How to Kettlebell Windmill Anatomical Analysis. The kettlebell Windmill develops flexibility and strength in the core muscles, shoulders and hips. Keep the kettlebell locked out and arms straight at all times and push your hip out in the direction of the kettlebell. Keep your eyes on the kettlebell all the way down and up. The movement in the left hip joint is extension with lateral/external rotation. The target muscle is the gluteus maximus. The hamstrings assist in extension and also assist in