Double-threshold training (Norwegian method)
Evidence: limited
Well described and physiologically plausible, but its superiority over simpler threshold work is not shown in controlled trials. An elite method built on a large base.
Double-threshold training places two submaximal threshold sessions in a single day, with lactate kept controlled in roughly the 2.0 to 4.0 mmol/L range so that a large volume of quality work accumulates without the cost of all-out efforts (Kelemen et al. 2024). It is associated with the Ingebrigtsen brothers and other Norwegian distance runners, and uses regular blood-lactate measurement to hold intensity precisely at threshold rather than above it.
The description of the method is well documented. Its claimed superiority over a single weekly threshold session is not established by controlled trials: the supporting evidence is observational, drawn from the training of already-elite athletes, and confounded by their talent and total volume (Casado et al. 2023). No randomised comparison shows double-threshold beats a simpler distribution.
The mechanism is plausible. Holding work just below the second threshold lets a runner do more total minutes at a high but sustainable intensity, raising the fraction of VO₂max that can be sustained, while limiting the fatigue and injury cost of harder running. Whether the doubled frequency adds anything beyond simply doing more controlled threshold volume is the open question.
A grassroots adaptation, sometimes called “Norwegian singles”, spreads the same sub-threshold idea across single daily sessions for runners who cannot train twice a day or hold elite volumes. It is popular on forums and is supported by anecdote rather than study.
The practical caution: this is an elite method built on a large aerobic base and careful monitoring. Copying its hardest features without that base is a common way to overreach. See overtraining.
What it looks like in practice
A double-threshold day
Morning: roughly 5 × 6 min or 6 × 5 min at controlled threshold effort, lactate held near 2.5 to 3.5 mmol/L. Afternoon: a second, often slightly faster set such as 10 to 12 × 3 min in the same lactate band. The defining feature is that neither session is run to exhaustion; intensity is capped precisely so a large volume of quality work accumulates without a single crushing effort.
Not a beginner method
This is built on a large aerobic base, twice-daily training, and lactate monitoring to hold the cap. Copied without those, especially the discipline to keep the work sub-threshold, it becomes two hard sessions a day and a fast route to overtraining. Most runners get the same idea more safely from a single weekly threshold session run strictly to effort.