Double threshold workouts are taking the running world by storm.
This is mostly thanks to the impressive success of Olympic and World 5k champion Jakob Ingebrigtsen of Norway, alongside his two older brothers with nearly as impressive credentials.
The unusual “Norwegian method” of training, first pioneered in the early 2000s by fellow Norwegian runner Marius Bakken, involves doing two threshold workouts in the same day: one in the morning and one in the evening: a so-called double threshold workout.
The basic idea behind double threshold is that this “clustering” of two workouts in the same day allows you to run a greater amount of interval work at threshold pace without the same amount of stress on your body that would occur if you tried doing all your threshold work in the same training session.
But, is double threshold all it’s cracked up to be?
It’s certainly popular, but whether it proves to be a long-term shift in training or a short-term fad depends on how well it really works.
As with many new trends in training, double threshold training has sparked the interest of sports science researchers, and some of the initial research into double threshold training is starting to trickle in.
So, in this article we’re going to look into some of the science to see if any of these claims about double threshold training are backed up by research.
Observational research on double threshold
Initial work on double threshold training was simply observational.
The title of a 2019 paper by Leif Tjelta, a researcher at the University of Stavanger in Norway, posed the key question: “Three Norwegian brothers, all European 1500 m champions: What is the secret?” [1].
After reviewing the training history and performances of all three Ingebritsen brothers, Tjelta pointed to three key training variables:
- progressive increases in mileage
- a significant fraction of training (over 20%) close to threshold
- and careful regulation of training intensity.
While observational research like this clearly has its limitations—not the least of which is the fact that all three brothers are, well, related to each other, and thus may not represent how the typical athlete responds to training—this initial work spurred more formal review articles and experimental studies.
Is internal load the key to double threshold?
Most runners think of “threshold” as a pace they can look up in a table. But the Norwegian method is different.
The Ingebritsens use a portable lactate meter to monitor workout intensity, targeting specific lactate levels (around 2.0 to 4.0 mM of lactate, depending on the workout) instead of specific paces.
A follow-up narrative article by Tjelta and a few other co-authors, including Marius Bakken himself, emphasized the importance of using an objective metric of internal load, such as lactate, as opposed to an external load metric like pace [2].
The benefit of targeting internal load, they argue, is that you can accumulate more volume at a fast pace without incurring excessive fatigue.
In this way, double threshold training allows you to run more of your volume at a fast pace, without the usual increase in fatigue that you’d get if all of that high-intensity work was above your second lactate threshold (a.k.a. LT2).
Lactate measurements are great if you can get them, but a portable lactate meter is a luxury that’s probably out of reach for most runners.
Can another internal loading metric, like heart rate, act as a surrogate? It’s not clear.
One big problem with heart rate, in comparison with lactate, is that the first and second lactate thresholds can occur at very different percentages of maximal heart rate, even in runners with similar fitness levels [3].
A better approach is comparing your heart rate against your own previous threshold workouts—that way, you can get a decent estimate of internal load without the problems associated with strict heart rate zones.
Experimental work: finding the right comparison for double threshold workouts
When considering whether double threshold training works, it’s important to ask “in comparison to what?”
One reason why runners might be finding success with the Norwegian approach is that it simply gives them permission to dramatically increase the total amount of high-quality aerobic running they do in a week.
So, it’s one thing to ask whether double threshold in comparison to your current training makes a difference, and another to ask whether the “double” part of double threshold is what makes the difference.
A new study published this summer in Frontiers in Physiology tackles this latter question [4].
The study compared a single 6 x 10 minute threshold workout versus two 3 x 10 minute sessions at 90% of second lactate threshold pace, separated by 6.5 hours of recovery.
The researchers tracked blood lactate, heart rate, and perceived exertion throughout both sessions.
The “single threshold” workout led to a distinctive pattern indicating a greater challenge later in the workout.
The single threshold method subjects had…
- a higher heart rate
- a greater rate of ventilation (i.e. heavier breathing)
- increased blood lactate levels
- and increased difficulty (to the tune of about one point on a 0–10 scale) in the last 30 minutes of the workout
Compared with the second double threshold session—which, remember, also represented minutes 30–60 of threshold running during the day.
Recovery metrics were different too.
Resting heart rate in the hour following the single threshold workout was higher versus after the double threshold session, and the runners reported greater fatigue and soreness the day after the single threshold session compared with the double threshold session.
Collectively, these results support one of the main claims behind the Norwegian method…
Splitting large threshold workouts into two shorter doubles allows you to cover more ground with less apparent physiological stress on your body.
Unanswered questions about double threshold training: what’s the injury risk?
We don’t want to make too much out of one study—the athletes were Norwegians, so they’d be clear-eyed about what hypothesis they were testing—the potential for a placebo effect is very real!
More importantly, though, a big unanswered question is whether double threshold has any advantages for injury prevention.
Less fatigue and soreness are promising directions, but these sensations are not necessarily indicators of injury risk.
Training volume and training intensity are the biggest drivers of injury risk [X], so at the end of the day, 60 minutes of threshold work is still 60 minutes of fast running from the perspectives of your bones and tendons, whether it’s done in one session or two.
It’s unclear whether any real recovery happens in just a few hours, so jumping into a huge increase in threshold volume could spell trouble from an injury perspective.
Recap
Double threshold training is a clear innovation in training that’s founded on a few key principles…
- accumulating a lot of running at speeds close to lactate threshold,
- focusing on internal load as opposed to external pace
- and splitting workout volume into two sessions in the same day.
These first two principles have strong support in the scientific literature.
Greater volumes of training, and greater amounts of threshold work, are both known to correlate with success in running, and the importance of measuring internal physiological load has long been recognized by physiologists.
The third principle—the benefit of splitting training volume into two sessions—is both the most innovative and the least well-understood component of the double threshold method.
Some initial experimental evidence suggests that the double threshold approach leads to less physiological stress on your body, compared with an equal amount of threshold work in a single training session, but whether double threshold training lowers injury risk remains unclear.
If you decide to try double threshold training, be mindful of your overall training volume, and your “volume of intensity,” i.e. how much total threshold running you do per week.
You don’t want to drastically increase either of these variables out of nowhere, no matter what kind of training you do.
If you want specific guidance, check out the article we wrote on how to properly incorporate double threshold workouts into your training.
