Final answer:
A properly designed kettlebell training routine combines strength training, cardiovascular exercise, and flexibility training.
Step-by-step explanation:
A properly designed kettlebell training routine combines aspects of: 1) Strength training: Kettlebell exercises like swings and snatches can help build muscular strength. 2) Cardiovascular exercise: Kettlebell workouts that involve continuous movement can improve cardiovascular health. 3) Flexibility training: Performing dynamic stretches with kettlebells can increase the range of motion of muscles and joints.
Therefore, the correct answer is 4) All of the above.