The Norwegian 4x4: Research, Considerations, and Practical Implementation
A simple way to incorporate HIIT across all modes of cardio
The Norwegian 4x4, a high intensity interval training protocol brought to light by Peter Attia, Rhonda Patrick, and other mainstream wellness personalities, has gained traction in fitness chatter. The original article, published in 2007 by a team of Norwegian researchers, examined 40 healthy adult men by placing them into one of four training groups:
Long, slow distance (known in the training world as LSD […not that kind], which is training at 70% max heart rate MHR) for 45 minutes
Lactate threshold (85% MHR) for 24.25 minutes
Your lactate threshold is the point at which your body cannot effectively clear the lactate from your system and it begins to accumulate. As you become more conditioned and your VO2 (maximal oxygen consumption during exercise) increases, your lactate threshold also increases. This means you can perform at a higher intensity for a longer period of time before reaching your threshold.
15/15 (15s at 90%+MHR, then 15s 70%MHR. Think of these as a fartlek - continuous running with a surge and slow tempo.)
47 repetitions were performed - which seems like a ton, until you do the math. It’s roughly 23 minutes per training session. Remember, these aren’t start and stop sprints. It’s continuous running with push pieces woven throughout.
4x4 (4min at 90%+MHR, with 3min 70%MHR - essentially an expanded version of group 3.). This is the Norwegian 4x4 protocol.
Participants used only their assigned style of training 3x/week for 8 weeks. Regardless of group assignment, all subjects utilized a 10 minute warm up and a 3 minute cool down with each training session.
Results
Both high intensity groups (3 & 4) demonstrated significant increases in VO2 max as a result of training. The 15/15 group increased VO2 by 5.5%, whereas the 4x4 group increased VO2 by 7.2%. There was no significant difference between the high intensity groups, indicating that both offer effective options for HIIT.
All four groups saw increases in their running economy. Additionally, stroke volume, a measure of cardiac efficiency that shows how much blood is pumped out by the heart, increased in the two HIIT groups as well.
Considerations
Much like strength training, those who are already well-trained will likely see a smaller increase in VO2 because the ceiling is already lower. Those who are deconditioned have the opportunity to see a substantial increase because they have more room to improve.
This is an 8 week training protocol, not a cohort study, meaning this group was not followed over time. Training maintenance, duration of training effect, and follow-up were not included.
Runners could have improved their running economy simply by training for 8 weeks.
Subjects were healthy males in their mid-20s. If you don’t fit this demographic (and even if you do), your mileage (pun intended), will vary.
This was a research study, which is why participants only engaged in the type of training per the group they were assigned to. This is NOT how training works in real life, but is necessary for scientific control to measure effect.
Practical Recommendations and my .02.
I took one of my indoor cycling classes through this protocol last week. It’s very easy to follow. Anyone can remember to do 4 blocks for 4 minutes and understand that they should feel like they’re working at an 8+/10 RPE. It’s also a protocol that can be used across any mode of exercise (running, cycling, rowing, etc.)
Like any HIIT training, this should be used as part of a well-balanced training program. Increasing your VO2 is an important part of conditioning, but it’s not the only goal. Research indicates that training volume should be established as part of one’s aerobic base. Training in Zone 2 (HR) provides opportunities for expanding volume while adequately recovering.
Research subjects only participated in a certain type of training for this study, so that the effects of their assigned training protocol could be measured without undue influence. This, of course, is not real life. So, if you’re someone who finds yourself only participating in high-intensity training, consider how your body is handling it. Training hard and training well are not synonymous terms.
I take my classes through a variety of interval sequences on HIIT days. Sometimes we work in 1:1, meaning equal parts work and rest intervals. Other days, we’ll extend them. The 4x4 protocol allows participants to really experience the intensity that’s intended by the interval.
When working in shorter blocks (e.g. 30 seconds), adrenaline can carry an exerciser through a single interval without experiencing the true physiologic response. Sure, heart rate increases, muscles become fatigued, etc., but having to settle into an uncomfortable push for four minutes helps exercisers - especially novice ones - really understand their own physiological response to HIIT. It also helps develop grit.
Bottom Line
Participate in HIIT (and use this protocol if you wish) 1-2 days per week with a minimum of one full day in between training sessions. Participate in low-moderate steady state cardio the other days of the week.
If you’re new to exercise, focus on 1 day of HIIT per week, and 30 minutes of low intensity, steady state cardio on as many other days as you’re able to tolerate. The 30 minutes can be accomplished in smaller increments, such as 3 separate 10 minute walks per day.
While HIIT training is an excellent way to improve heart health, don’t use HIIT training as your only form of exercise. It’ll result in overtraining and will negatively impact your fitness outcomes in the long run.
Don’t forget about strength training. At minimum, 2 days per week of total body resistance training working all muscle groups should be part of your routine. But don’t overthink it. A total body weight training session can be accomplished in 30 minutes. More on that, soon!
Have you used this style of HIIT training before? Interested in trying it out? Let me know in the comments what you think!
Simply Fit is a free, weekly newsletter written by Dr. Amanda Durall, a Kinesiology professor, fitness professional, and busy mom of three aiming to simplify exercise science and deliver practical recommendations to help you achieve your fitness goals. Want more free content like this delivered straight to your inbox? Subscribe for weekly training tips, technique overviews, and more evidence-based fitness content!