Long Slow Distance Swim (Swim LSD)
The Long Slow Distance swim is the Thursday cardio session in the 26-week NSW preparation program. It is a continuous swim at a low to moderate intensity, and its distance grows by 100 yards every week, from 1,000 yards in week 1 to 3,500 yards in week 26.
How the Session Is Defined
The LSD swim follows the same intensity rule as the LSD run. The pace should feel relatively easy and relaxed, and the guide uses the Talk Test as the check, which in the water means an effort where you could speak a short sentence at the wall without gasping. The session is about duration, not speed, and it builds the endurance and stroke efficiency that every other swim session depends on. Warm up with 5 to 10 minutes of easy stroking. The guide names a practical goal of swimming 1 to 1.25 miles without stopping, and the program passes that mark around week 13, when the LSD swim reaches 2,200 yards.
How It Progresses Across 26 Weeks
The swim adds 100 yards each week with no plateaus. Week 1 prescribes 1,000 yards. Week 6 prescribes 1,500 yards, week 12 prescribes 2,100 yards, week 18 prescribes 2,700 yards, and week 26 prescribes 3,500 yards. In a 25-yard pool that is 40 lengths in week 1 and 140 lengths in week 26. The progression is linear by design: a fixed 100-yard step keeps the weekly increase small enough to absorb while the total triples and a half over the program. If you have more than 26 weeks, the guide suggests adding a second LSD swim rather than lengthening CHI or interval sessions.
Where It Sits in the Week and How to Pace It
Swim LSD falls on Thursday, paired with a core and push-sit-pull calisthenics session. It sits between the Tuesday CHI swim and the Saturday interval swim, so it is the recovery-oriented swim of the week. Use the combat sidestroke or breaststroke, the two strokes the PST permits, and treat the distance as technique practice under mild fatigue. Count strokes per length and try to hold that count steady from the first length to the last. A rising stroke count signals a decaying stroke, and the LSD swim is the session where you have the time and the low intensity to fix it.
Progression across the program
| Week | Prescription |
|---|---|
| 1 | 1,000 yards |
| 6 | 1,500 yards |
| 12 | 2,100 yards |
| 18 | 2,700 yards |
| 26 | 3,500 yards |
Swim the whole LSD distance in combat sidestroke and alternate sides every length. Symmetry built at this easy pace is what keeps your stroke honest when the 500-yard swim gets hard.
Related Terms
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.
The combat sidestroke (CSS) is a hybrid swimming technique developed for military applications that combines elements of sidestroke, freestyle, and breaststroke. It is the preferred stroke for the PST 500-yard swim and the primary swimming technique used throughout BUD/S training and NSW operations.
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 Continuous High Intensity swim is the Tuesday cardio session in the 26-week NSW preparation program. It is a sustained swim at roughly 90 to 95 percent of the fastest pace you could hold for the prescribed time, with no rest inside the block, and it grows from one 15-minute block in week 1 to two 20-minute blocks in week 26.
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