Training · Running
Intervals, reps and threshold: reading a session
A written running session is a compressed notation, and once you can read it the whole family of them becomes obvious. Every structured session is four numbers — how many, how long, how hard, how much recovery — and changing any one of them changes what the session is for.
A session written as "6 × 800m off 90 seconds" says: run 800 metres, recover for 90 seconds, and do that six times. Sometimes the recovery is given as a distance instead — "off 400m jog" — which means the recovery is itself a slow 400 metres rather than a fixed time.
The intensity is often left out of the notation because it is assumed from context. In a plan it will be stated somewhere; at a club the coach says it. If nobody has told you how hard, the session is incompletely specified and it is reasonable to ask.
The four variables, and what each one controls:
- Repetitions
- How manyTotal volume of hard work. More repetitions at the same intensity makes the session longer rather than harder.
- Duration or distance
- How long each one isLonger efforts push the session towards sustained work; shorter ones towards speed.
- Intensity
- How hardThe variable people change without meaning to. Running the first repetition too hard changes the entire session.
- Recovery
- How long betweenShortening recovery makes a session harder without changing anything else, and is the usual way a session is progressed.
- Short, fast repetitions with full recovery — Efforts of well under a minute, taken with enough recovery to run each one properly. The intent is mechanical — running fast, relaxed — rather than cardiovascular.
- Classic intervals — Efforts of a few minutes with incomplete recovery, so fatigue accumulates across the set. The archetypal hard session.
- Threshold or tempo work — Either one sustained effort of twenty minutes or more, or long blocks with very short recoveries. Sustained and uncomfortable rather than hard.
- Fartlek — The same idea with the measurement removed — surges within a continuous run, judged by feel and landmarks. Useful when a track or a measured stretch is not available.
- Hill repetitions — Intervals run uphill. The gradient limits the pace, which for many runners makes it easier to reach a hard effort without over-striding.
A structured session is run correctly when the last repetition is roughly as fast as the first. That is the whole quality standard, and it is what separates a session from a race against yourself.
A set that starts fast and degrades has been run at the wrong intensity, and the useful information from it is that the intensity was wrong rather than that you are unfit. This is why experienced runners deliberately start a set feeling as though they are holding back — the pace that feels correct on repetition one is nearly always too fast for repetition six.
Questions this guide answers
Listed so you can tell at a glance whether this is the page you wanted. HobbyHQ keeps one guide per question family rather than a page per phrasing.
- what does 6 x 800m mean in running
- how do I read a running session
- what is the difference between intervals and reps
- what is a threshold session
- how long should recovery between intervals be
- what is a pyramid session in running
Part of Running. Last reviewed 2026-08-30.