Which of the following activities is most appropriate for re-establishing or maintaining an adequate fitness level for safe diving?

Engaging in workouts in a pool with a mask, fins, and snorkel three times per week is particularly beneficial for maintaining and re-establishing fitness levels relevant to diving. This activity closely simulates the conditions divers experience underwater, allowing them to enhance their swim efficiency and comfort in the water. Using fins provides an effective method to build leg strength and improve propulsion while swimming, which is crucial for conserving energy while diving.

Additionally, practicing with a snorkel and mask helps divers become more accustomed to breathing through a snorkel and managing buoyancy, which is vital when transitioning to diving. The repetitive motions involved in swimming laps with this equipment improve cardiovascular fitness and lung capacity, both of which are essential for safe diving practices.

While running on a treadmill can enhance cardiovascular fitness and weightlifting can promote muscular strength, these activities do not replicate the specific skills and adaptations needed for diving. Swimming laps without equipment offers beneficial overall conditioning but lacks the specific focus on diving mechanics that fins and snorkels provide. Thus, the exercise regimen outlined supports both physical fitness and proficiency in essential diving skills, making it the most appropriate choice for divers.