How it works
The aim is to spend a lot of time right at the edge where lactate starts to accumulate (LT2), without tipping over it. Held under control, this intensity drives strong aerobic adaptations while keeping the session repeatable rather than exhausting. The key word is controlled: you stay just below the line, not racing it.
The Norwegian double-threshold twist
Pioneered by Marius Bakken and later popularised by Jakob Ingebrigtsen and the Norwegian triathletes, the method runs two sub-threshold sessions in the same day (for example morning and evening). Blood lactate is measured between intervals to keep each rep slightly below LT2, so the athlete accumulates a very high weekly volume of quality work without the wreckage that one all-out session would cause.
How to apply it
Most amateurs cannot do this literally: it depends on a lactate meter and the time and recovery for big volume. Borrow the principle instead. Run threshold intervals at a pace or heart rate you could just barely sustain for an hour, stay disciplined about not pushing harder, and keep the rest of your week genuinely easy. Controlled threshold plus mostly easy mileage captures most of the benefit.
FAQ
What is the lactate threshold (LT2)?
LT2 is the intensity above which blood lactate rises faster than your body can clear it. In practice it sits close to the hardest steady effort you could hold for about an hour, and it is the anchor point for threshold training.
Do I need a lactate meter to train this way?
To follow the Norwegian method literally, yes, because the whole point is keeping each rep precisely below LT2. Without one you can approximate the same zone using heart rate or pace, aiming for a controlled effort that feels comfortably hard rather than maximal.
Is double-threshold training right for beginners?
Generally no. Two quality sessions in a day demand high fitness, careful fueling, and real recovery time. A beginner gains more from a single controlled threshold session per week plus easy aerobic running, which is the safe way to borrow the idea.