Continuous High Intensity Swim (Swim CHI)
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.
How the Session Is Defined
A CHI swim means swimming without stopping for a set number of minutes at approximately 90 to 95 percent of the maximal pace you could hold for that duration. The guide calls the effort very demanding but not totally exhausting, an 8 or 9 on a scale of 1 to 10. At a low fitness level one block of 15 to 20 minutes is sufficient. As fitness improves, the session becomes two blocks with a recovery of about half the work time between them, during which you keep moving with an easy stroke rather than resting on the wall. Warm up for 10 to 15 minutes or more, and use the combat sidestroke or breaststroke.
How It Progresses Across 26 Weeks
The CHI swim matches the CHI run schedule. Weeks 1 through 12 use one block that grows by one minute every two weeks: 15 minutes in weeks 1 and 2, 16 in weeks 3 and 4, 17 in weeks 5 and 6, 18 in weeks 7 and 8, 19 in weeks 9 and 10, and 20 in weeks 11 and 12. From week 13 there are two blocks: 2 x 12 minutes in weeks 13 through 15, 2 x 14 in weeks 16 through 18, 2 x 16 in weeks 19 through 21, 2 x 18 in weeks 22 through 24, and 2 x 20 in weeks 25 and 26. Total work time rises from 15 to 40 minutes.
Where It Sits in the Week and How to Pace It
Swim CHI is fixed on Tuesday, paired with a lower-body and push-sit-pull session, and it is the first swim of the week. Pick an effort you can hold for the full block. The PST swim must finish under 12:30, so even the 15-minute block of week 1 is longer than the test, at a pace a little slower than test pace. The session teaches you to hold a hard, steady stroke past the distance where the PST ends. In the two-block weeks, match the second block to the first. Beyond 26 weeks, do not extend the duration; increase the pace instead.
Progression across the program
| Week | Prescription |
|---|---|
| 1 | 15 min |
| 6 | 17 min |
| 12 | 20 min |
| 18 | 2 x 14 min |
| 26 | 2 x 20 min |
Count laps during the CHI block and write the total down. Yards per 20 minutes at a steady effort is the cleanest week-to-week measure of whether your combat sidestroke is getting more efficient.
Related Terms
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 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.
The Interval swim is the Saturday cardio session in the 26-week NSW preparation program. It consists of repeated 100-yard efforts at a pace slightly faster than your current 500-yard swim pace, separated by recovery periods, and the repeat count grows from 4 in week 1 to 10 by week 13.
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.
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