This article is part of our 5K session series. Each article covers one session: how it’s structured, what it does, when to run it, and what to run around it. This one teaches the skill that decides most races: starting controlled and finishing strong.
The session at a glance
| Phase | Build |
| Distance | 3.1 miles (5km) |
| Structure | Five 0.62-mile (1km) splits, each one quicker than the last |
| Effort | Starts at 4 out of 10, finishes at 9 out of 10, with only the final few hundred yards at 9 |
| Heart rate | Zones 1–2 at the start, through zone 3 into zone 4, touching the top of zone 4 only at the very end |
| Intensity domains | Moderate, moving into heavy |
| Typical time | 25–40 minutes, plus warm-up walk and cooldown |
Where it fits: the four phases of 5K training
We split 5K training into four phases. Each has a different job:1
- Base (6–8 weeks): build your aerobic engine and get your legs used to regular running. Almost everything is easy.
- Build (4–6 weeks): add harder sessions, like threshold intervals, on top of the base.
- Peak (2–3 weeks): sharpen with work at or near 5K race pace.
- Taper (7–10 days): cut the volume, keep a little speed, and arrive at the start line fresh.
In the build phase, the progression run sits alongside threshold intervals and the block progression run. It’s the gentlest of the three hard sessions, because only the last two splits (1.2 miles / 2km) reach threshold, and only the final few hundred yards go above it, which makes it a good way to ease into harder running.
Intensity domains: moderate, heavy and severe
Heart rate zones describe what your watch shows. Intensity domains describe what’s happening inside your body. Exercise physiologists split running effort into three domains, separated by two thresholds:2, 3
| Domain | Where it sits | What happens | Roughly |
|---|---|---|---|
| Moderate | Below your first lactate threshold | Lactate stays close to resting levels. You can keep going for hours. | Zones 1–2, easy running |
| Heavy | Between your first lactate threshold and critical speed | Lactate rises, then levels off. Hard but sustainable. | Zones 3–4, steady to threshold |
| Severe | Above critical speed | No steady state. Fatigue builds until you have to stop, usually within minutes. | Zone 5, 5K race pace for most runners |
Critical speed is the fastest pace at which your body can still reach a steady state. In this series, “threshold” means running just below it, at the top of the heavy domain.
The progression run starts low in the moderate domain and climbs steadily through the heavy domain, touching the top of it only in the final stretch and stopping just short of severe.
Purpose, goal and target
Purpose: to practice speeding up on tired legs, and to spend quality time in the heavy domain without the fatigue of a full threshold session.
Goal: five 0.62-mile (1km) splits, each quicker than the one before, with the last split the fastest, at threshold, rising to 9 out of 10 only in the final few hundred yards, and still under control.
Target, split by split:
| Split (0.62 mile / 1km each) | Effort | Heart rate | Feels like |
|---|---|---|---|
| 1 | 4/10 | Zones 1–2 | Very easy, full conversation, almost too slow |
| 2 | 5–6/10 | Zone 2 | Easy, still conversational, a little more purposeful |
| 3 | 7/10 | Zone 3 | Steady, short sentences |
| 4 | 8/10 | Zone 4 | Threshold, comfortably hard, a few words at a time |
| 5 | 8/10, then 9/10 for the final 220 yards (200m) only | Zone 4, touching the top of zone 4 at the very end | Threshold, then hard, single words at most |
Each split is 0.62 mile (1km), so the session is five splits rather than three mile laps. Press the lap button on your watch at each split, or set auto-lap to 0.62 mile (1km) for this session.
How to run it
- Walk briskly for 5 minutes to raise your heart rate gradually.
- Split 1 (first 0.62 mile / 1km): run very easy, at 4 out of 10. This is your warm-up, the same effort as a zone 2 easy run, and it should feel almost too slow.
- Splits 2–4 (0.62 to 2.5 miles / 1 to 4km): step up one zone each split, from easy in zone 2 to steady in zone 3, then threshold in zone 4. Aim for roughly 25–40 seconds per mile (15–25 seconds per kilometer) quicker each time. The jumps don’t need to be exact; the direction matters more than the numbers.
- Split 5 (final 0.62 mile / 1km): hold threshold, 8 out of 10, for most of the split. In the final 220 yards (200m) only, let the effort rise to 9 out of 10, at the top of zone 4. This is hard but not a sprint; you should still be running tall, relaxed and quick.
- Cool down with 5–10 minutes of easy jogging or walking.
Heart rate lags behind effort, so in the later splits it will still be rising when you step up again. Pace each split by effort, and use heart rate to check you didn’t go too hard too early.
What it does to your body
The session builds aerobic fitness at every level. The early splits do what a zone 2 run does, and the later ones push toward the top of your aerobic range, where your body gets better at clearing lactate.4
It also teaches pacing. The fastest way to ruin a 5K is to go out too fast, and a progression run trains the opposite habit, patience early and strength late. Reviews of pacing research suggest that in races lasting more than a few minutes, an even pace, or a slightly faster second half, tends to work better than a fast start.5 The last 0.62 mile (1km) comes when you’re already warm and slightly fatigued, which is how the final stretch of a race feels.
Because most of the run is below threshold, it’s less tiring than a full interval session. That makes it a good session to alternate with threshold intervals, or a good choice in a week when life is busy.
Timing
Run it once a week at most, and if you’re newer to running, not in the same week as another hard session. A typical 6-week build phase runs:
- Weeks 1–2: threshold intervals as the hard session.
- Weeks 3–4: alternate threshold intervals and the progression run week to week.
- Weeks 5–6: the block progression run takes over as the key session.
Mid-week or the weekend both work, with easy days or rest either side. Use a flat, familiar route, because hills make it impossible to judge whether you’re getting quicker.
Once the session feels controlled, aim to run each split a little quicker than last time at the same effort. Keep the 9 out of 10 push to the final few hundred yards; stretching it out turns the session into a race.
Matching sessions
For newer runners, the progression run replaces threshold intervals as the week’s hard session:
| Day | Session |
|---|---|
| Monday | Rest |
| Tuesday | 3.1 miles (5km) easy + strides |
| Wednesday | Rest or cross-training |
| Thursday | 3.1-mile (5km) progression run |
| Friday | Rest |
| Saturday | 4.3-mile (7km) zone 2 easy run |
| Sunday | Rest or an easy walk |
More experienced runners can run both threshold intervals and the progression run in the same week, with at least two days between them, for example intervals on Tuesday and the progression run on Saturday, with the zone 2 easy run on Sunday. Build slowly; adding intensity and mileage at the same time is a common route to injury. See building weekly mileage safely.
Back-to-back: the day before and the day after
The day before: rest, or the easy run with strides, is best. Avoid a hard or long session. If your legs are tired, you won’t be able to speed up, and the session loses its point.
The day after: rest or active recovery is best. A zone 2 easy run, kept easy, is usually fine, since the progression run costs less than a full threshold session. Avoid another heavy-domain session, like threshold intervals or the steady tempo run, because recovery from efforts above easy running takes noticeably longer.6
Common mistakes
- Starting too fast. If the first split isn’t easy, there’s nowhere to go, and you’ll finish flat instead of fast.
- Jumping too far too soon. Big jumps in splits 2 and 3 leave nothing for the finish, so keep the steps small.
- Racing the last split. Threshold is 8 out of 10, and the 9 out of 10 push is a few hundred yards, not the whole split. If you finish gasping, you went into the severe domain.
- Slowing down. If a split is slower than the one before, you pushed too hard earlier. Note it and start easier next time.
- Stopping dead. Always jog or walk it down afterward.
Pacing your first progression run
The session is 3.1 miles (5km), with each 0.62-mile (1km) split quicker than the last, from 4 out of 10 up to threshold and a brief 9 out of 10 push at the very end. It moves through every heart rate zone, from the moderate domain into the heavy domain, touching the top of zone 4 only in the final stretch and stopping just short of severe. What it teaches is patient pacing and a strong finish, the pattern behind most good 5K races. Pace by effort, take small steps, and keep the last split controlled. Use it as the gentlest hard session of the build phase, alternating with threshold intervals.
This article is general information, not medical or coaching advice. If you feel chest pain, dizziness or unusual breathlessness while running, stop and talk to a doctor.
References
- Issurin VB. New horizons for the methodology and physiology of training periodization. Sports Medicine, 2010. doi.org
- Jones AM, Burnley M, Black MI, Poole DC, Vanhatalo A. The maximal metabolic steady state: redefining the ‘gold standard’. Physiological Reports, 2019. doi.org
- Poole DC, Burnley M, Vanhatalo A, Rossiter HB, Jones AM. Critical power: an important fatigue threshold in exercise physiology. Medicine & Science in Sports & Exercise, 2016. doi.org
- Faude O, Kindermann W, Meyer T. Lactate threshold concepts: how valid are they? Sports Medicine, 2009. doi.org
- Abbiss CR, Laursen PB. Describing and understanding pacing strategies during athletic competition. Sports Medicine, 2008. doi.org
- Seiler S, Haugen O, Kuffel E. Autonomic recovery after exercise in trained athletes: intensity and duration effects. Medicine & Science in Sports & Exercise, 2007. doi.org
