You can borrow the Norwegian approach with one workout a day. The trick is a narrow effort band that most amateurs miss in both directions. It’s harder than easy, but it’s well short of a race-pace grind.
Most blogs call this “LT1 training.” That’s wrong. Your LT1 (first lactate threshold) is the point where lactate starts to rise, near 2 mmol/L. You can hold it for hours. The Norwegian “sub-threshold” work sits above that and below your LT2 (second lactate threshold), the effort you can hold for about an hour.
In short: sub-threshold lives between LT1 and LT2, and it tops out around LT2, never past it.
What the Norwegian singles method actually is
The Norwegian singles method is a one-session-a-day version of the Norwegian threshold model. The original elite version used double days: two threshold sessions on the same day. Singles keep the controlled intensity and drop the second session. You get 2 to 3 sub-threshold sessions a week, and everything else stays easy.
If you want the two-a-day original, read the running-only double-day version. If you wonder whether doubles are worth the recovery cost, see the recovery cost of two-a-days.
Here is the actual window from the main review. Casado and colleagues define the lactate-guided threshold work as 2 to 4.5 mmol/L, split into two bands. Translation: a lactate number is just a tidy way to say “hard enough to matter, easy enough to repeat.”
Typical running sessions from the Norwegian coach Marius Bakken look like this. They include 5 x 6 min at about 2.5 mmol/L with 1 min rest, and 10 x 1000 m at about 3.5 mmol/L with 1 min rest. The elite group ran 150 to 185 km a week, with roughly 80% of it easy.
Those are elite numbers. Don’t copy them.
The mistake: drifting from sub-threshold into LT2
Think of a car on a long climb. Hold the engine at a steady, strong rev and you reach the top fine. Floor it and you overheat halfway. Sub-threshold work is the steady rev. LT2 and above is the floor.
The common error isn’t going too easy. It’s overshooting. Once you push past about 4.5 mmol/L you stop doing controlled work and start doing a race effort. You’ll need more recovery, and the next session suffers.
Short rest is part of the design. One minute between reps keeps the effort steady without letting you fully recover. That’s why a session can feel “comfortably hard” even in the last rep.
Heart rate doesn’t care about your plans. On a hot day it creeps up while pace stays flat, so you’ll feel like you’re working harder than the target. Use a mix of signals, not one. Our post on Zone 2 science explains why the easy base underneath all of this matters.
What the research does and doesn’t prove
The authors of the main review say it plainly: no controlled trial tests the full model. It’s observational. It describes 1500 m and 5000 m runners, not triathletes. They also warn that zone boundaries must be tested for each person, and that injury and overtraining risk is real.
The only supporting intervention they cite is small. Eight well-trained middle-distance runners added 20 minutes a week at about 4 mmol/L for 8 weeks. In short: a tiny study backs the idea of a bit of threshold work, not the whole system.
Triathlon evidence is thin, too. We found no trial of this model in triathletes, so any triathlon version is borrowed from running. Our comparison of polarized vs pyramidal training covers the debate.
The Norwegian triathlon group is a useful reality check. Coach Olav Aleksander Bu said the program moved from mostly threshold-oriented work toward a more base-heavy, pyramidal shape. Even the people who made it famous dialed it back.
So treat this as sound coaching logic. It isn’t proven.
Sub-threshold sessions for swim, bike and run
The run sessions below come from Casado. The swim and bike rows are coaching guidance from AthleteOS, not research.
| Sport | Example session | Rest | Target feel | Source |
|---|---|---|---|---|
| Bike | 3 x 10-12 min or 4 x 10 min | 1-2 min easy spin | RPE 5-6, just under FTP | Coaching guidance |
| Run | 5 x 6 min | 1 min jog | About 2.5 mmol/L | Bakken, via Casado 2023 |
| Run (advanced) | 25 x 400 m | 30 s | About 3.5 mmol/L | Bakken, via Casado 2023 |
| Swim | 8 x 200 m or 10-20 x 100 m | 10-15 s | Steady, just under your best hold | Coaching guidance |
Your FTP (Functional Threshold Power) is the highest power you can hold on the bike for about an hour. Sub-threshold bike work sits just under it. In short: hard enough to feel it, easy enough to repeat three more times.
The bike is the best place to start. It’s low impact, and power gives you tight control. Running costs the most fatigue per minute, so cap it by effort, not by pace on hills. For swimming, short rest is the whole point.
Never port a run threshold to the bike or the pool. Thresholds differ by sport and by how much muscle you use.
A 10-hour week with two sub-threshold sessions
This is an example week, not a prescription. Aim for roughly 15 to 25% of weekly time in the band, with the rest easy. That range is coaching guidance. The practitioner claim for singles is 20 to 25%.
| Day | Session |
|---|---|
| Mon | Easy swim, strength |
| Tue | Bike: 4 x 10 min sub-threshold |
| Wed | Easy run |
| Thu | Swim: 8 x 200 steady, short rest, then easy run |
| Fri | Rest or easy spin |
| Sat | Long easy bike, short brick |
| Sun | Run: 5 x 6 min sub-threshold, then easy running |
Take Dana, 41, training for a 70.3 on 9 hours a week. She’d been racing every interval at full effort and felt flat by Thursday. She cut hard work to two sub-threshold sessions, one bike and one run, and kept the rest in Zone 1. Over six weeks she felt fresher and stopped dreading Tuesday. This is an illustrative example, not a study result.
How to find your band without a lactate meter
You don’t need a finger prick. A recent study of 165 recreational runners found that pace-based threshold estimates landed within about 0.4 to 0.6 km/h of lab values when athletes used real max tests. With guessed maximums, the error grew to about 1.0 to 1.1 km/h. Translation: test properly and your estimate is decent, guess and it’s off by a lot.
Use three checks together: power or pace, heart rate, and effort. Aim for 5 to 6 out of 10. If the last rep feels like a race, you’ve overshot.
AthleteOS sets your zones separately for swim, bike and run, then plans the week around them. Use those zones to place two sub-threshold sessions on days that aren’t already hard. It doesn’t measure lactate. You can start a free trial here. For a simpler zone model first, see 3-zone vs 5-zone training.
Who should skip it
Skip it if you’re new to structured training. Build a base first. Skip it when you’re injured or in a heavy block of racing. And if you’ve got only 4 to 6 hours a week, one sub-threshold session is plenty.
For long-course racing, easy volume matters most. Don’t trade it for intervals.
Easy is the engine. Sub-threshold is the tune-up.