What are some effective strategies for building up cardiovascular endurance in swimming, particularly for individuals who are accustomed to explosive, short-interval workouts but struggle with sustained efforts over longer distances? Are there specific drills or exercises that can help improve lactate threshold and increase overall endurance, or is it more a matter of gradually increasing volume and intensity over time? Are there any differences in approach between sprint-focused swimmers and distance swimmers when it comes to building endurance, or are the underlying physiological principles the same? How do swimmers balance the need for endurance work with the need for strength and power training, and are there any specific strength exercises that can help improve swimming endurance? What role do nutrition and recovery play in building swimming endurance, and are there any specific strategies or techniques that can help optimize these aspects of training?