Training plans throw around terms like tempo run, fartlek and interval as if everyone already knows what they mean — because to the person who wrote the plan, they do. If you've ever stared at a schedule that says "5 x 1000m" or "30 min @ tempo" and had no idea what pace that actually means, this is the glossary that fills in the gap. Each section below defines one workout type, explains what it's training in your body, and gives a simple example of what it looks like in practice.
Easy run: the default of every plan
An easy run is a run at a pace that feels genuinely comfortable — comfortable enough to hold a full conversation without gasping between sentences. It isn't a warm-up shuffle and it isn't "as slow as possible"; it's simply the effort your aerobic system can sustain for a long time without piling up real fatigue. For most runners, most weeks, this is the majority of total running volume, not a minor category next to the "real" workouts.
What it trains is the aerobic base: the heart's stroke volume, the density of capillaries feeding your muscles, and the mitochondria that burn oxygen and fat for fuel. None of that develops from hard efforts alone — it needs time spent at an effort low enough to sustain for a while. A commonly cited guideline, sometimes called the 80/20 split, suggests keeping roughly four-fifths of weekly volume at this easy effort. Treat it as a rough rule of thumb rather than a number to hit exactly.
- The conversation test. If you can't speak in full sentences, you're not running easy.
- It should feel sustainable, not just doable. You should be able to picture running another 10 minutes at the same effort without dread.
- Slower than you think is usually right. Most runners who are told to "run easy" still run it too fast the first few times.
Recovery run: a specific, deliberately very easy run
A recovery run is an easy run with a job to do: it's scheduled the day after a hard effort — a race, a long run, a tough interval session — and run at an effort even lower than a normal easy day. The distinction from a regular easy run is mostly about timing and purpose, not a different kind of running. The point isn't to build fitness on its own; it's to move blood through tired legs without adding meaningful new stress on top of what's already there.
- It should feel almost too slow. If a recovery run feels like a normal easy run, it's probably not slow enough.
- Shorter is normal. Many plans keep these to 20–30 minutes rather than a full easy-run length.
- A full rest day is a fine substitute. If your legs are genuinely trashed, skipping the recovery jog for actual rest is rarely the wrong call.
Long run: the week's longest effort, defined briefly
The long run is exactly what it sounds like: the single longest run of the week, usually run at easy-to-moderate effort, building the endurance and time-on-feet tolerance that shorter runs can't provide on their own. It's central to every half marathon and marathon plan in particular, and it deserves a full breakdown of its own rather than a quick summary here — see Training Plans by Distance for how the long run progresses week to week at each distance. This glossary just defines it for completeness, since the other workout types below are often described relative to it.
Tempo run: sustained effort, comfortably hard
A tempo run is a continuous effort held at a pace that's often described as "comfortably hard" — noticeably harder than easy, but not an all-out sprint. A useful reference point: it's roughly the pace a reasonably fit runner could hold if racing for about an hour, though the exact number varies a lot by fitness level. You can talk in short phrases at tempo effort, not full sentences.
What it trains is the lactate threshold — the effort level at which your body shifts from clearing lactate about as fast as it's produced to accumulating it faster than it can clear, which is what makes a hard effort start to feel genuinely unsustainable. Training right around that threshold, repeatedly, is what pushes the threshold itself higher over time, letting you hold a faster pace before things start to hurt.
A simple tempo structure
- 10–15 minutes easy, to warm up
- 20–30 minutes continuous at tempo effort — comfortably hard, not a sprint
- 10 minutes easy, to cool down
Interval run: hard efforts, broken into pieces
Interval training means repeating a hard effort for a set distance or time, with an easy jog or rest between each repeat — for example, 6 x 800m at a hard effort with a 400m easy jog for recovery between them. Unlike a tempo run, which is one continuous block, intervals are broken up on purpose: the recovery jog lets you hold a noticeably harder pace than tempo effort for each individual piece, because you're not asking the body to sustain that intensity without a break.
What intervals train is speed and VO2 max — roughly, the maximum rate your body can take in and use oxygen during hard exercise. That's a different stimulus than threshold work: intervals push well above the pace you could hold continuously, in chunks short enough to be manageable, then repeat that stimulus multiple times in one session. Shorter, faster repeats (200m–400m) tend to emphasize raw speed; longer repeats (800m–1600m) sit closer to VO2 max work.
A simple interval structure
- 10–15 minutes easy, to warm up, plus a few short strides
- 6 x 800m at a hard effort, with a 400m easy jog between each repeat
- 10 minutes easy, to cool down
Fartlek: speed play, no stopwatch required
Fartlek is Swedish for "speed play," and that's a fair description: it's an unstructured version of interval training where the hard surges are picked by feel or by landmarks — run hard to that tree, or the next lamp post, or until this song ends — rather than by a measured distance or a precise time on a watch.
The training effect overlaps with formal intervals, but the appeal is different. A fartlek is a good way to ease into structured speed work if the idea of hitting exact splits feels intimidating, and it's a good option any day when a rigid, watch-driven session feels like more structure than you want. Nothing about a fartlek needs a track, a GPS pace alert, or a plan — just an easy run with some faster surges dropped in.
A simple fartlek structure
- Start with 10–15 minutes at easy effort, as a warm-up
- Pick 6–10 surges of roughly 30 seconds to 2 minutes at a hard-but-controlled effort, choosing when to start and stop by feel or by a landmark ahead
- Jog easy between surges until you feel ready for the next one — there's no fixed recovery time
- Finish with 5–10 minutes easy to cool down
How these fit together in a typical week
Most weeks in most plans lean heavily on easy running, with one tempo or interval session, one long run, and recovery runs or full rest days placed around the harder efforts so they don't stack on top of each other. Two hard days back to back — say, an interval session the day after a tempo run — usually means neither one gets a fair effort, because the legs are still carrying fatigue from the first.
| Workout | Effort | Mainly trains | Simple example |
|---|---|---|---|
| Easy run | Conversational | Aerobic base | 30–60 minutes at easy pace |
| Recovery run | Very easy | Recovery after a hard day | 20–30 minutes, slower than normal easy |
| Long run | Easy to moderate | Endurance, time on feet | The week's longest single run |
| Tempo run | Comfortably hard | Lactate threshold | 20–30 minutes continuous at tempo effort |
| Interval run | Hard, broken up | Speed, VO2 max | 6 x 800m hard, 400m jog recovery |
| Fartlek | Hard, by feel | Speed work, less rigidly | 6–10 unmeasured surges within an easy run |
The mix shifts with the distance you're training for. A 5K build tends to lean harder on tempo and interval work relative to its overall mileage, since the race itself is run close to threshold pace from start to finish. A marathon build leans further toward easy volume and the long run, using tempo and interval sessions more sparingly to protect the legs for the miles that matter most. Browse 5K races, 10K races, half marathons or marathons once you've settled on a distance — or start from the full list of states if you're not sure where you'll be racing yet.
Where to go next
This page is deliberately just the vocabulary. For the full week-by-week structure — how many weeks of each workout type a 5K, 10K, half marathon or marathon plan actually needs, and how that changes if you're starting from zero — see Training Plans by Distance. And since pace alone doesn't make a hard session productive, Running Form: Cadence and Breathing covers the related skills — how you breathe and how quickly your feet turn over — that make tempo and interval effort feel more controlled.