Long Slow Distance (LSD) Training
Long Slow Distance (LSD) training is a cardio methodology that emphasizes sustained, moderate-intensity effort over extended durations. In BUD/S preparation, LSD sessions build the aerobic base required for long swims, runs, and the prolonged physical output demanded throughout SEAL selection.
How LSD Training Works
LSD workouts are performed at a conversational pace — typically 60-70% of maximum heart rate. The goal is duration over intensity. A typical LSD run might be 4-6 miles at a steady, sustainable pace, while an LSD swim could be 1,000-2,000 yards of continuous effort. The pace should feel manageable enough to maintain for the entire duration without significant fatigue.
Aerobic Base and BUD/S Demands
BUD/S places enormous demands on the aerobic system. Candidates spend hours in cold water, run miles in soft sand, and perform sustained physical tasks throughout the day. Without a strong aerobic base, the body cannot recover between efforts and fatigue accumulates rapidly. LSD training builds the cardiovascular foundation that supports all other training modalities.
LSD vs. Interval Training
LSD and interval training serve complementary purposes. LSD develops the aerobic engine — the body's ability to sustain effort over time. Interval training develops speed and anaerobic capacity — the ability to push hard in short bursts. The NSW preparation program uses both methods across the 26-week cycle, with LSD dominating the early phases and intervals increasing as fitness improves.
Don't skip LSD days to do harder workouts. Your aerobic base is what keeps you going when BUD/S grinds you down over hours and days.
Related Terms
Interval training is a cardio method that alternates between high-intensity work periods and active recovery periods. In the NSW preparation program, interval sessions target running and swimming speed by training the body to sustain faster paces through repeated timed efforts.
Continuous High Intensity (CHI) training is a cardio method that sustains a near-maximal effort for a set duration, typically 15-20 minutes. In the NSW preparation program, CHI sessions bridge the gap between LSD endurance work and short-burst interval training by developing the ability to maintain a fast pace without rest breaks.
The 500-yard swim is the first event of the Physical Screening Test (PST) and measures a candidate's aquatic endurance. Performed using either the combat sidestroke (CSS) or breaststroke, it tests the sustained swimming capacity required for BUD/S water-based evolutions.
The 1.5-mile run is the final event of the Physical Screening Test (PST) and measures a candidate's running speed and cardiovascular endurance. Performed after the swim and calisthenics events, it tests the ability to produce a fast run effort on fatigued legs — a skill directly relevant to BUD/S demands.
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