Interval Swim (Swim INT)
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.
How the Session Is Defined
An interval swim alternates 100-yard work intervals with recovery periods that last 2 to 2.5 times as long as the work. During recovery you keep moving with an easy stroke rather than hanging on the wall. The target pace comes from the swim interval pace chart and should be about 2 seconds per 100 yards faster than the pace you held in your most recent 500-yard swim. A candidate who swam 500 yards in 10:30 has a base 100-yard pace of 2:06, so the interval target is about 2:04. Warm up for 10 to 15 minutes or more before the first repeat, and swim the repeats with the combat sidestroke or breaststroke.
How It Progresses Across 26 Weeks
The repeat count follows the same schedule as the interval run. Weeks 1 and 2 prescribe 4 repeats. The count rises by one every two weeks: 5 in weeks 3 and 4, 6 in weeks 5 and 6, 7 in weeks 7 and 8, 8 in weeks 9 and 10, 9 in weeks 11 and 12, and 10 from week 13 through week 26. Ten is the ceiling; the guide says not to swim more than 10 intervals in a session. Once you can hit all 10 repeats in the prescribed time, the progression moves to pace, and you swim the same 10 repeats a little faster each week.
Where It Sits in the Week and How to Pace It
Swim INT closes the training week on Saturday, paired with a lower-body and push-sit-pull session. The guide wants even splits: little variation between your fastest and slowest repeat, and the last repeat the fastest of the set. Every fourth or fifth week you may use shorter, more frequent efforts, for example 16 to 20 repeats of 50 yards, to raise intensity. Because the session comes two days after the Thursday LSD swim, the stroke should feel grooved. Record every repeat time, because the chart only moves when you retest the 500-yard swim.
Progression across the program
| Week | Prescription |
|---|---|
| 1 | 4 x 100 yards |
| 6 | 6 x 100 yards |
| 12 | 9 x 100 yards |
| 18 | 10 x 100 yards |
| 26 | 10 x 100 yards |
Push off the wall on every repeat exactly as you will in the PST, with no extra glide. Interval swims are the only place in the week where turn speed gets rehearsed at race intensity.
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.
The swim interval pace chart is the swim half of Table 1 in the NSW Physical Training Guide. It converts your most recent 500-yard swim time into a target 100-yard repeat time and a recovery window for the Saturday interval swim, so the intensity of every interval session tracks your tested fitness.
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 Interval run is the Wednesday cardio session in the 26-week NSW preparation program. It consists of repeated quarter-mile efforts at a pace slightly faster than your current 1.5-mile run pace, separated by recovery periods, and the number of repeats grows from 4 in week 1 to 10 by week 13.
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