Interval Running

What is it?

Interval running covers a range of session formats built around short-to-medium hard efforts, separated by recovery. Unlike a single fixed format, we run several different types of interval session — including fartleks, pyramid sessions, and single-duration reps — each targeting a slightly different part of your fitness.

All of our interval sessions are time-based rather than distance-based. This is deliberate: running "4 minutes hard" is inclusive to every ability, since a faster runner and a newer runner both get the same training stimulus and the same recovery structure, just at their own pace. Nobody is left finishing early or struggling to complete a set distance — everyone runs the same session, together.

The different formats we use

Fartlek sessions (Swedish for "speed play") mix varied efforts and recoveries within one continuous run, rather than fixed, repeated blocks. Two of our regular fartlek formats:

  • Monaghetti Fartlek — a descending threshold effort: 10 min warm-up, then 2 x 1:30 min, 4 x 60 sec, 4 x 30 sec, and 4 x 15 sec, all at threshold effort, finishing with a 10 min cooldown. The efforts get shorter as the session goes on, which keeps the pace and focus sharp even as fatigue builds.
  • Gerschler Fartlek — named after coach Woldemar Gerschler, a pioneer of structured interval training. Ours repeats a descending-recovery block three times: 30 sec hard efforts with recovery jogs that shrink from 90 sec down to 15 sec across the block. As the rest gets shorter, the session gets progressively tougher without the work effort itself changing.

Timed Pyramid Intervals build up and back down in effort length — for example, 4 min, 3 min, 2 min, 1 min, then back up through 2 min, 3 min, and 4 min, with 1 min jog recovery between each. The changing rep length keeps the session varied and helps you learn to control pace across efforts of different durations, all within one session.

Anaerobic Intervals are short, sharp reps with generous recovery, designed to build repetition-style speed and power rather than sustained aerobic effort — for example, 2 x 1:30 min followed by 10 x 30 sec efforts, with a longer warm-up to prepare properly for the higher intensity.

Single Duration Intervals are the simplest format — repeating the same effort and recovery length throughout, for example 10 x 1:30 min. This is a good baseline session for tracking progress over time, since the format doesn't change week to week, only the pace or number of reps does.

How it works

All of these formats train your VO2max and your ability to hold pace under fatigue, but the varying structures stress your system slightly differently:

  • Fartleks with descending recoveries (like the Gerschler format) progressively increase the difficulty of maintaining effort as the session goes on, without ever increasing the length of the hard reps themselves
  • Pyramids force you to adjust and control pace across changing durations within a single session
  • Short anaerobic reps with long recovery target power and speed with less aerobic fatigue accumulation
  • Single duration sessions provide a stable, repeatable format that makes it easy to track fitness improvements over time

Across all formats, recovery is typically jogged rather than fully stopped, which keeps you moving and clearing fatigue actively — similar in principle to threshold sessions, though the effort and rep lengths here are higher intensity and shorter.

Why it matters

Varying the interval format keeps training both physically well-rounded and mentally engaging. Different structures challenge pacing, focus, and recovery in different ways, which helps prevent staleness and targets more than one physiological system across a training block — rather than only ever training the same rep length at the same intensity.

Because everything is time-based, these sessions also scale naturally to a group of mixed abilities — everyone runs the same session structure, working just as hard relative to their own fitness, without needing to adjust the plan itself.

Example session — beginner

Single Duration Intervals

  • 10 min warm-up
  • 10 x 1:30 min interval effort, jogged recovery between each
  • 10 min cooldown

Example session — advanced

Timed Pyramid Intervals

  • 10 min warm-up
  • 4 min interval, 1 min jog
  • 3 min interval, 1 min jog
  • 2 min interval, 1 min jog
  • 1 min interval, 1 min jog
  • 2 min interval, 1 min jog
  • 3 min interval, 1 min jog
  • 4 min interval
  • 10 min cooldown

How to pace it

Interval effort should be hard enough that holding a conversation isn't possible, but controlled enough that you can repeat the effort consistently across the whole session — not an all-out sprint. For the shorter anaerobic-style reps (15–30 sec), effort can push closer to maximal, since the longer recovery allows fuller recovery between reps.

Coaching tip

Don't judge a session by the first rep — formats like the Monaghetti and Gerschler fartleks are designed to get progressively harder as the recoveries shrink or the reps repeat, even though the work effort doesn't change. Save something for the back end of the session rather than going out too hard on rep one.

Related sessions

Interval running is just one part of a balanced week. Explore the other effort types:

  • Threshold Running — sustained efforts that raise your lactate threshold, including our 10-week progressive series
  • Hill Running — a lower-impact way to build strength and power
  • Easy Running — the foundation that makes every harder session possible

Not sure what pace to run your intervals at? Try our Training Paces Calculator.