Short intervals occupy the space between VO2max work and pure speed training. They're faster than long intervals, briefer, and target a slightly different blend of adaptations: aerobic ceiling development combined with pace-specific speed and fast-twitch fibre recruitment.
Where long intervals (3 to 5 minutes) maximise time at peak oxygen consumption, short intervals (90 seconds to 3 minutes) spend less time at VO2max per rep but run faster. The pace is roughly 3K to 5K race effort. This higher speed recruits more fast-twitch muscle fibres, generates greater neuromuscular demand, and improves running mechanics at paces closer to top-end speed.
For marathon runners, short intervals are a secondary tool. Long intervals are the primary VO2max builder. Short intervals add a speed dimension that keeps the neuromuscular system sharp and develops the upper end of the fitness spectrum.
What They Develop
VO2max (partial). Each rep drives oxygen consumption upward, but 90 seconds to 3 minutes isn't always long enough to reach true VO2max before the rep ends. The cardiovascular stimulus is real but less concentrated than in longer intervals. Across a full session, you still accumulate meaningful time at high oxygen consumption.
Speed and neuromuscular power. The faster pace forces more aggressive muscle fibre recruitment, quicker ground contact, and more elastic energy return. These adaptations improve running economy at every pace, including marathon pace. A runner who can comfortably hold 3:45/km for 800m repeats has neuromuscular reserves that make 5:15/km feel relaxed.
Lactate tolerance. Short, fast efforts produce high lactate levels. Repeated exposure trains the body to buffer and clear lactate more efficiently. This shifts the threshold upward, improving the sustainable pace for longer efforts.
Mental toughness at pace. There is a specific skill in holding a fast pace when the legs are heavy and the lungs are burning. Short intervals practice this more directly than long intervals because the pace is faster and the discomfort is sharper.
Common Formats
800m repeats. The classic short interval. 2:30 to 3:30 per rep depending on fitness. 4 to 6 reps with 90 seconds to 2 minutes jog recovery. Targets the overlap between VO2max and speed.
600m repeats. Slightly faster, slightly shorter. 1:45 to 2:30 per rep. 5 to 8 reps with 90 seconds recovery. More emphasis on speed and neuromuscular recruitment.
2-minute repeats. Time-based rather than distance-based. Useful when you don't have access to a measured track. 4 to 6 reps with 90 seconds to 2 minutes recovery.
Mixed sessions. Some coaches combine short and long intervals in the same session: 2 x 4 minutes followed by 4 x 90 seconds, for example. This works across the VO2max spectrum in a single workout. Useful during peak phase when training economy matters.
The Pacing Challenge
Short intervals are harder to pace correctly than long intervals. The temptation to sprint is stronger because the reps are brief and the pace is fast. Runners frequently start too aggressively, burn through the first 2 reps, and then watch quality collapse through the remaining set.
The check: your last rep should be at the same pace as your first. If the gap between fastest and slowest rep is more than 5 to 8 seconds per 400m, the session wasn't controlled. Consistency across reps, not maximum speed on any single rep, is what produces the training effect.
Target pace is 3K to 5K race effort. Not all-out. If you feel like you're sprinting, you're running too fast for this workout. The effort should be hard, clearly above threshold, but sustainable for the prescribed rep duration.
When in the Training Cycle
Base phase. Not recommended. The same reasoning as long intervals applies: the aerobic system and structural resilience need to be developed first.
Build phase. Introduced after long intervals are established, typically 3 to 4 weeks into the build. Can replace a long interval session every other week to add variety and speed stimulus, or can follow 2 to 3 long interval reps in a mixed session.
Peak phase. Useful for maintaining speed and top-end fitness while the primary training focus shifts to race specificity. Sessions may shorten: 4 x 800m rather than 6 x 800m.
Taper. A single short, sharp session (3 x 600m, for example) in the first week of taper can maintain sharpness without generating meaningful fatigue. After that, strides handle the neuromuscular maintenance.
Short Intervals vs. Long Intervals
| Short (90s to 3 min) | Long (3 to 5 min) | |
|---|---|---|
| Pace | 3K to 5K effort | 5K to 10K effort |
| Primary target | VO2max + speed | VO2max (pure) |
| Time at VO2max per rep | Less (ramp-up time is a larger fraction) | More |
| Neuromuscular demand | Higher (faster pace) | Moderate |
| Lactate production | Higher | Moderate |
| Recovery needed | Slightly less per rep | Slightly more per rep |
| Role in marathon training | Secondary | Primary |
Most marathon runners should prioritise long intervals. Short intervals add speed and variety but aren't the core VO2max stimulus.
Practical Guidelines
- Warmup: 15 to 20 minutes easy, plus 4 to 6 strides (strides matter more before short intervals, since the pace is faster).
- Reps: 4 to 8 repetitions of 90 seconds to 3 minutes.
- Intensity: 3K to 5K race effort. RPE 8.5 to 9.
- Recovery: 90 seconds to 2 minutes easy jog. Shorter than long-interval recovery because the reps are shorter.
- Cooldown: 10 to 15 minutes easy.
- Terrain: Flat. Track is ideal for accurate pacing at these shorter distances.
- Frequency: Once per week at most, and often alternating with long intervals rather than additional.
- The day after: Easy or recovery run.