Can training a muscle group six times a week work better than training that same muscle group three times a week?
To most people, the idea sounds completely outrageous.
Working a muscle group six days a week is just going to wreck your joints, beat up the CNS and leave you overtrained and burned out.
But there’s some intriguing research to suggest that the idea isn’t as crazy as you might think.
The study, known as The Frekvensprosjektet (Norwegian for Frequency Project) has yet to reach the pages of a peer-reviewed journal. As such, important details about how the Norwegian Frequency Project was set up are hard to come by.
The Norwegian Frequency Project
A group of 16 Norwegian powerlifters – 13 men and 3 women – was assigned to one of two groups. Both groups followed exactly the same training program, with one key difference.
The first group trained three times per week. Group two split each workout into two sessions, performing six shorter workouts over the course of the week.
Put another way, lifters in both the 3-day and 6-day groups did exactly the same amount of work. It was just distributed differently throughout the week. To keep total training volume the same, the group training three times a week performed twice as many sets in each workout.
After 15 weeks, it was the 6-day group who saw the greatest improvements.
In fact, strength gains in the squat, deadlift and bench press were roughly double those seen in the 3-day group.
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The figure below shows the combined change in strength across the three lifts. Each circle and square represents the results for one subject, while the horizontal line represents the group average.
As well as measuring strength gains, the researchers also looked at changes in the thickness of vastus lateralis (one of the thigh muscles) along with the cross-sectional area (CSA) of the quadriceps.
Again, it was the 6-day group who built the most muscle, posting a 4% gain in the CSA of the quadriceps. Surprisingly, subjects in the 3-day group gained an average of precisely nothing. The results are shown below.
Those findings strike me as very odd. Why did so many lifters in the 3-day group lose muscle?
Take a look at the figure showing the percentage change in cross-sectional area. You’ll notice that it shows the results from just five of the eight subjects in the 3-day group.
Where are the results from the other three? And what effect would their results have had on the group average?
Something else that stands out is the wide range of results from person to person.
In terms of muscle thickness, three subjects in both groups got roughly the same results, gaining around 5%.
Two subjects in the 6-day group made substantially faster progress than everyone else. In fact, one lifter posted an increase in muscle thickness that was roughly three times greater than the group average.
Such a big variation in results, even in people following exactly the same training program, has shown up in other studies on the same subject.
Some people respond extremely well to strength training. We call them high responders. Some will get “good but not great” results, and are known as medium responders. Others – the low responders – will take a lot longer to build the same amount of muscle.
This raises a question.
Would the low responders in the 3-day group have got better results if they’d trained six days a week?
We don’t know. Nor do we know if the high responders in the 6-day group would have made the same gains if they’d been in the 3-day group.
In other words, it’s possible that these subjects would have been low and high responders regardless of training frequency, and the reason for the superior gains in the 6-day group was that a higher number of low and medium responders were assigned by chance to the 3-day group.
The results from the Norwegian Frequency Project look compelling. But, there are several reasons why I don’t think you should drop everything and immediately start training each muscle group six times a week.
For one, the subjects taking part in this study weren’t overweight beginners or recreationally active college students, who are usually the guinea pigs for this type of research.
Instead, they were young powerlifters with an average age of 21. All had competed in national powerlifting competitions in the six months prior to starting the trial.
This tells us they were probably first in line when the “strong and muscular” genes were being handed out. That same set of powerlifter-friendly genetic traits may also have made it more likely that they were able to thrive on a program that involved training a muscle group six days a week.
Just like the findings from studies using untrained beginners can’t be extended to elite athletes, the findings from studies of elite athletes don’t always apply to those who weren’t given the same genetic gifts.
What’s more, muscle growth was measured only in the thighs. We know from other studies that the quadriceps respond differently to an increase in training volume compared to muscles in the upper body [1, 2]. The same may well hold true for training frequency.
In addition, there was no “intermediate” training frequency. Would hitting a muscle group 4-5 days a week, for example, have worked just as well as training it six days a week?
Remember, the main goal of the Norwegian Frequency Project was to look at strength gains. The type of training that maximizes strength gains isn’t necessarily the type of training that works best for building muscle.
In the interview shown in the video below, one of the guys involved in the Norwegian Frequency Project doesn’t recommend training a muscle six days if muscle growth is the main goal.
It’s important to remember that many millions of people have successfully gained muscle using a variety of different training methods.
The results from the Norwegian Frequency Project shouldn’t be interpreted to mean that working each muscle group six times a week is now the official “best way” for everyone to train.
What they do suggest is that the range of effective training frequencies, particularly for those with several years of training behind them, may be a lot wider than previously thought.
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