5K Build Phase: The Block Progression Run

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 is the longest and most demanding session of the build phase: two continuous blocks, tempo then threshold, back to back.

The session at a glance

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.

The block progression run comes at the end of the build phase, once threshold intervals and the steady progression run feel controlled. It’s the session that turns short bursts of threshold running into sustained threshold running.

Intensity domains: moderate, heavy and severe

Exercise physiologists split running effort into three domains, separated by two thresholds:^{2, 3}

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.

After the warm-up, this whole session sits in the heavy domain, with the tempo block in the lower half and the threshold block at the very top. The skill is staying on the right side of that upper boundary for 1.9 miles (3km).

Purpose, goal and target

Purpose: to build the ability to sustain threshold effort continuously, and to practice holding a hard pace when you’re already tired from the block before it.

Goal: a controlled tempo block, followed by a threshold block that is quicker than the tempo and evenly paced from start to finish.

Target:

If you know your 5K time, threshold pace is a little slower than 5K race pace, and tempo pace sits roughly halfway between that and your easy pace.

How to run it

Warm-up: 1.2 miles (2km)

1. Walk briskly for a few minutes, then jog the 1.2 miles (2km) easily in zone 2.
2. Optional: finish with 2–3 short strides. A good warm-up improves performance in the hard running that follows.⁴

Tempo block: 1.9 miles (3km)

3. Build into tempo effort over the first few hundred yards. Settle at 7 out of 10.
4. Hold it evenly. Your heart rate will creep up slowly through the block, which is normal.⁵ Keep the effort steady rather than chasing a heart rate number.

Threshold block: 1.9 miles (3km)

5. Step up straight into threshold effort, with no break. The change should feel clear but not dramatic.
6. Hold 8 out of 10 and aim for even mile splits. The last 0.6 mile (1km) will feel much harder than the first at the same pace, and learning to hold it is what the session is for.
7. If your breathing becomes ragged and you can’t speak at all, you’ve crossed into the severe domain. Ease off slightly.

Cooldown: 0.6 mile (1km)

8. Jog easily, then walk for a few minutes.

For your first attempt, it’s fine to shorten the blocks to 1.2 miles (2km) each and build up to 1.9 miles (3km) over the following weeks.

What it does to your body

Sustained running close to threshold is one of the most direct ways to push your threshold up, so you can hold a faster pace before fatigue builds rapidly.⁶ Threshold intervals break the effort into short reps with recoveries. This session asks for 1.9 miles (3km) continuously, which is much closer to the demands of a 5K.

The tempo block tires you slightly before the threshold block starts, just as the first half of a race tires you before the finish, so you practice running on pre-fatigued legs.

Because the whole session stays in the heavy domain, you get a lot of quality work without the deep fatigue of severe-domain intervals. That’s why it suits the build phase, before race-pace work arrives in the peak phase.

Timing

Run it once a week, as the week’s only hard session. It replaces threshold intervals and the progression run rather than being added to them. A typical 6-week build phase runs:

• Weeks 1–2: threshold intervals as the hard session.
• Weeks 3–4: alternate threshold intervals and the steady progression run.
• Weeks 5–6: the block progression run as the key session.

Schedule it for a day when you’re fresh and have time; at 50–70 minutes, it’s your longest session of the week. Eat a normal carbohydrate-based meal 2–3 hours before, and take water on warm days.

The route should be flat, measured and uninterrupted, because traffic crossings and hills make it hard to hold even blocks. A track or a long flat path is ideal.

Matching sessions

In the late build phase, the block progression run becomes the week’s key session:

This week has more total mileage than earlier build weeks, because this session is 1.9 miles (3km) longer than threshold intervals. If that’s a big jump for you, shorten the Saturday easy run for the first week or two. See building weekly mileage safely.

Back-to-back: the day before and the day after

The day before: rest is best, and a short easy run or the easy run with strides is fine. Avoid anything hard or long. This session needs fresh legs; on tired legs the threshold block quickly drifts into the severe domain.

The day after: rest or active recovery is best. Two days later, the zone 2 easy run is fine, kept easy, and walk if your heart rate goes too high. Avoid any heavy-domain running for at least two days, because recovery from sustained efforts above easy running takes noticeably longer than recovery from easy runs.⁷ Eat a meal with carbohydrates and protein within a couple of hours, and prioritize sleep; see sleep and running performance.

Common mistakes

• Running the tempo block too fast. If tempo creeps up to threshold, the second block will fall apart, so hold 7 out of 10.
• Racing the threshold block. It’s 8 out of 10, not all-out, and finishing the block in the severe domain adds a lot of fatigue for little extra benefit.
• Uneven splits. A fast first half of the block and a slow second half means you started too hard. Aim for even.
• Stopping between blocks. The step from tempo to threshold should be continuous; stopping turns it into a different session.
• Adding it too early. Wait until threshold intervals and the steady progression run both feel controlled.

When you’re ready for the blocks

The full session is a 1.2-mile (2km) warm-up, 1.9 miles (3km) at tempo, 1.9 miles (3km) at threshold and a 0.6-mile (1km) cooldown: 5.6 miles (9km) in total. After the warm-up it sits entirely in the heavy domain, finishing just below the line into severe, and it builds the ability to sustain threshold effort continuously on tired legs, much closer to the demands of a 5K. Hold tempo at 7/10, step up to threshold at 8/10, and keep the splits even. Save it for the last weeks of the build phase, run it as the week’s only hard session, and follow it with rest or easy running for two days.

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

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4. Bishop D. Warm up II: performance changes following active warm up and how to structure the warm up. Sports Medicine, 2003. doi.org
5. Coyle EF, González-Alonso J. Cardiovascular drift during prolonged exercise: new perspectives. Exercise and Sport Sciences Reviews, 2001. doi.org
6. Faude O, Kindermann W, Meyer T. Lactate threshold concepts: how valid are they? Sports Medicine, 2009. doi.org
7. 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