Interval Run (Run INT)
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.
How the Session Is Defined
An interval run alternates short, intense work periods with periods of recovery. The work interval is a quarter mile. The recovery period lasts 2 to 2.5 times as long as the work interval, and during recovery you keep moving at a slow jog or brisk walk rather than stopping. The target pace comes from the run interval pace chart: it should be about 4 seconds per quarter mile faster than the pace you held in your most recent 1.5-mile run. A candidate who ran 1.5 miles in 10:30 has a base quarter-mile pace of 1:45, so the interval pace is about 1:41. Warm up for 10 to 15 minutes or more before the first repeat.
How It Progresses Across 26 Weeks
The repeat count is the variable that grows. Week 1 and week 2 prescribe 4 repeats. The count rises by one every two weeks: 5 repeats 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 onward. The count holds at 10 repeats for the last 14 weeks of the program. The guide says never to run more than 10 intervals in a session. Once you can complete 10 repeats at the prescribed time, progress by running the same 10 repeats a little faster each week.
Where It Sits in the Week and How to Pace It
Run INT falls on Wednesday, paired with a core and push-sit-pull calisthenics session. The guide asks for consistency: keep little variation between your fastest and slowest repeat, and pace the session so that the last repeat is the fastest. Going out hard on repeat one and fading is the common error. Every fourth or fifth week you may swap the format for shorter, more frequent efforts, for example 16 to 20 repeats of 220 yards. After the last repeat, extend the cool-down until your breathing is easy and your heart rate is near its resting value.
Progression across the program
| Week | Prescription |
|---|---|
| 1 | 4 x 1/4 mile |
| 6 | 6 x 1/4 mile |
| 12 | 9 x 1/4 mile |
| 18 | 10 x 1/4 mile |
| 26 | 10 x 1/4 mile |
Log every repeat time, not just the session. The chart pace only updates when you retest the 1.5-mile run, so your interval log is the earliest evidence that you are ready for a faster bracket.
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 run interval pace chart is Table 1 of the NSW Physical Training Guide. It converts your most recent 1.5-mile run time into a target quarter-mile repeat time and a recovery window for the Wednesday interval run, so every candidate trains at an intensity calibrated to their current fitness.
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.
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.
Ready to start training?
ZeroPhase turns the 26-week NSW training guide into a daily digital program with PST tracking and automatic plan adjustments.
Start Your TrainingNot ready to start? Take the standards with you.
Get the PST standards and week 1 of the plan by email. Occasional training emails after that, nothing weekly, one-click unsubscribe.