The short answer
The Norwegian model runs threshold work twice a day because it treats lactate as a control signal rather than a byproduct. When the workload is held just below the intensity at which blood lactate begins to accumulate faster than it can be cleared, the session can be repeated with limited autonomic and muscular cost. The twice-daily structure is not a magic interval prescription. It is a way to accumulate a large volume of submaximal aerobic work while keeping each individual session far enough from maximal that the next session is still productive.
The polarization debate often gets framed as a choice between easy and hard. That framing misses the middle. The Norwegian approach is not a rejection of easy training or of high-intensity work. It is a claim about where the largest sustainable adaptation stimulus sits for a well-trained endurance athlete, and about how to dose that stimulus without tipping into overreaching.
What lactate actually tells you
Blood lactate is the product of a balance between production and clearance. At low intensities, clearance keeps pace with production and lactate stays near baseline. As intensity rises, glycolytic flux increases and lactate appearance in the blood rises faster than removal. The first rise above baseline is often called the first lactate threshold or LT1. The steeper rise is LT2, sometimes called the maximal lactate steady state or the second threshold.
LT1 is not a wall. It is a marker of a shift in the balance. Training just below LT1 allows a high volume of work with low sympathetic stress and low glycogen cost per minute. Training between LT1 and LT2 raises the aerobic stimulus further but shortens the recovery window. Training above LT2 accelerates glycogen depletion and autonomic strain.
The Norwegian model uses frequent lactate sampling to keep sessions in the narrow band around LT1 and, in some sessions, just below LT2. The point is not to chase a number. The point is to calibrate the session to the individual athlete’s current physiology on that day.
Why twice a day
Two threshold sessions in a day are not simply two hard workouts stacked together. They are usually structured as a longer morning session and a shorter, controlled afternoon session, or vice versa. The rationale is volume accumulation at an intensity that is high enough to stimulate central and peripheral adaptations but low enough that the athlete can repeat it.
The adaptations in question include increased mitochondrial density, capillary growth, and improved lactate clearance capacity. These are driven by sustained submaximal work, not by maximal efforts alone. A single threshold session can provide part of that stimulus. Two sessions in a day can provide more total time near threshold without requiring the athlete to spend that time at an intensity that would compromise the next day.
This is where the model differs from a simple polarized distribution. Polarized training typically concentrates work at low intensity and high intensity, with little in the middle. The Norwegian model argues that for some athletes, especially those with a well-developed aerobic base, the middle is not a dead zone. It is a productive zone if the intensity is controlled precisely enough.
The evidence is mixed, and here is why
Direct comparisons between high-volume threshold training and polarized training are difficult to interpret. Studies differ in athlete caliber, training history, session structure, and how thresholds are defined. A study that finds polarized training superior may have used a threshold intensity that was too high, turning the middle zone into a hard zone. A study that finds threshold training superior may have used a polarized high-intensity dose that was too low to drive adaptation.
The retrieved sources for this article are limited. The PubMed records available at the time of writing returned cookie-consent pages rather than full abstracts, so I cannot cite specific effect sizes from those records. The Frontiers in Physiology article page was retrieved but the excerpt available does not contain the full text. That means the strongest claims here are mechanistic and practical, not statistical. Where the evidence is mixed, I will say so.
What is reasonably well established is that training intensity distribution is not a single variable. Total volume, session frequency, recovery, nutrition, and individual response all interact. The Norwegian model is one way to manage those interactions. It is not the only way, and it is not universally superior.
Lactate-guided prescription in practice
The practical procedure is straightforward in principle and demanding in execution. The athlete performs a step test or a series of controlled efforts to establish the lactate curve. From that curve, the coach identifies the workload associated with LT1 and the workload associated with LT2. Threshold sessions are then prescribed at or slightly below those workloads.
During a session, lactate is sampled at intervals. If lactate rises above the target range, the athlete reduces power or pace. If lactate falls below the target range, the athlete increases it. The goal is to keep the session in the intended band, not to hit a fixed number regardless of how the athlete feels.
This requires a lactate meter, test strips, and practice. It also requires the athlete to accept that the prescribed intensity may change from day to day. A session that felt easy yesterday may feel hard today at the same power. The lactate response is one way to detect that before the session becomes a recovery debt.
What about heart rate and RPE
Heart rate is useful but lagging. It responds to heat, hydration, caffeine, and autonomic state. RPE is useful but subjective. Neither replaces lactate for fine-grained threshold control, but both are useful for context. A rising heart rate at a stable lactate and stable power may indicate heat stress or dehydration. A rising RPE at stable lactate and stable power may indicate accumulating fatigue.
HRV is a recovery marker, not a prescription tool. It can help flag when an athlete is not recovering, but it does not tell you what intensity to use in a session. The Norwegian model uses lactate for intensity control and other markers for recovery monitoring.
Individual differences matter
Lactate kinetics vary between athletes. Muscle fiber type distribution, capillary density, mitochondrial content, and training status all influence how much lactate is produced and cleared at a given workload. Two athletes with the same threshold power may have very different lactate curves and very different recovery profiles.
This is why a fixed percentage of threshold power is a blunt instrument. A percentage of FTP or a percentage of max heart rate may put one athlete below LT1 and another athlete above LT2. Lactate-guided training is an attempt to individualize the dose.
Training status also matters. A highly trained athlete with a large aerobic base can often tolerate more threshold volume than a less trained athlete. The same twice-daily structure that works for a professional may be excessive for an amateur with a full-time job and limited sleep.
When high-volume threshold work goes wrong
The risk is overreaching. High-volume threshold training sits in a narrow band between productive stress and excessive strain. If the intensity drifts upward, if recovery is insufficient, or if nutrition and sleep are inadequate, the athlete can accumulate fatigue without accumulating adaptation.
Signs of trouble include persistent fatigue, declining power at the same lactate, rising RPE at the same workload, disturbed sleep, and loss of motivation. These are not unique to threshold training. They are generic overreaching markers. The difference is that high-volume threshold training can produce them gradually, without the obvious warning of a failed interval session.
This is why the Norwegian model is not a shortcut. It requires monitoring, adjustment, and a willingness to reduce volume when the markers say so. Without that, it is just a lot of moderate-hard training.
What the model does not claim
The Norwegian model does not claim that polarized training is wrong. It does not claim that high-intensity work is unnecessary. It does not claim that threshold training is superior for all athletes. It claims that for some well-trained endurance athletes, a high volume of precisely controlled threshold work can produce a strong adaptive response with manageable recovery cost.
That claim is plausible on mechanistic grounds. It is supported by some observational and practical evidence. It is not supported by a large body of randomized controlled trials showing superiority over other distributions. The evidence is mixed, and the reasons for the mix are methodological as much as physiological.
Practical takeaways
If you are considering a threshold-heavy approach, start with accurate threshold testing. Do not assume that a percentage of FTP or max heart rate is your LT1 or LT2. Measure lactate if you can. If you cannot, use the talk test and RPE with caution, and be conservative.
Build volume gradually. Twice-daily threshold sessions are not a starting point. They are a progression for athletes who already tolerate high training volumes and recover well.
Monitor recovery. Use sleep, resting heart rate, HRV, and subjective energy as context. If markers trend in the wrong direction, reduce volume before you reduce intensity.
Do not treat the model as a religion. The goal is to find the distribution that works for you, not to copy a professional’s schedule. The Norwegian model is one tool among several.
FAQ
Is the Norwegian model just polarized training with more threshold work?
Not exactly. Polarized training deliberately minimizes time in the middle zone. The Norwegian model deliberately occupies the middle zone, but at a controlled intensity. The difference is in how precisely the middle zone is defined and monitored.
Can I do twice-daily threshold sessions without a lactate meter?
You can, but you lose the main control variable. Heart rate and RPE can work as rough guides, but they are less precise. If you cannot measure lactate, be more conservative with volume and progress more slowly.
Does the Norwegian model work for time-crunched athletes?
The model depends on volume and recovery. If you have limited training time and high life stress, a lower-volume polarized or pyramidal approach may be more practical. The model is not a good fit for everyone.
What is the biggest mistake people make with threshold training?
Going too hard. Threshold training is not about suffering. It is about accumulating time at a controlled intensity. If you are finishing threshold sessions exhausted, you are probably above LT2, not at LT1.
How do I know if I am overreaching?
Persistent fatigue, declining performance, rising RPE at the same workload, and disturbed sleep are common signs. If these persist for more than a few days, reduce training load and reassess.