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.
However, I’ve been able to put some of the pieces together with the help of conference proceedings (here and here), Matt Perryman’s excellent book Squat Every Day, as well as a couple of articles by Borge Fagerli and Martijn Koeveots.
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.
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 – tend to progress a lot more slowly.
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.
What’s more, the results from the Norwegian Frequency Project haven’t been replicated in other trials.
In a follow-up study, researchers from the University of South Florida compared two programs that involved training three or six days per week.
Subjects taking part in the study were young men in their early twenties who’d been lifting weights for at least six months.
In order to be eligible for the study, they had to be able to squat at least 125% of their bodyweight, bench press 100% of their bodyweight, and deadlift 150% of their bodyweight.
So, they weren’t the typical untrained beginners who are often used in this type of research. But they were a long way from the competitive powerlifters used in the Norwegian Frequency Project.
The men were split into two groups, and trained either three or six days per week. The amount of training performed by both groups was identical, but was spread out differently.
For the men training three days per week, each workout lasted an average of two hours, while the men training six days a week took around an hour to complete each workout.
This time, there was no significant difference in strength or size gains between the two groups.
Men in the 3-day and 6-day groups got roughly the same results, with the researchers concluding that “training frequency appears to follow the law of diminishing returns, as high frequency (6 days per week) resistance training does not appear to offer additional strength and hypertrophy benefits over lower frequency (3 days per week), when volume and intensity are equated.”
Interestingly, the high frequency group did see faster gains in muscle mass – 5.7 pounds (2.6 kilograms) versus 3.7 pounds (1.7 kilograms) in the low frequency group.
If you want to learn more about this research, the authors of the study discuss their results here.
It was a similar story when a team of Brazilian researchers compared training a muscle once a week with a full-body workout performed five times a week, Monday through Friday.
In order to be eligible for the study, subjects had to have been training for at least three years, be able to squat at least 150% of their bodyweight, and bench press at least 100% of their bodyweight.
The once-a-week group did two exercises per workout for 5-10 sets per exercise, while the full-body group did 11 exercises for 1-2 sets per exercise. Both workouts lasted a little over 30 minutes.
Again, there were no significant differences in terms of strength or size gains between the two groups – 10-15 sets distributed over the course of five days increased muscle mass and strength similarly to the same number of sets performed once a week.
However, as with the University of South Florida study, the full-body group did register a slightly greater increase in lean body mass than the once a week group.
In another trial, Croatian researchers found that training a muscle either three or six times a week, under volume-equated conditions, led to similar gains in muscle size and strength.
Beginner, Intermediate or Advanced?
The length of time you’ve been training also appears to have an impact on how your muscles respond to a higher training frequency.
If you’re just starting out, you may do just as well with a conventional training program, where you hit each muscle 2-3 times a week.
In a group of untrained beginners, lifting weights once or three times a week for 11 weeks led to very similar gains in muscle size.
That is, in terms of muscle growth at least, six sets performed once a week worked just as well as two sets performed three times a week.
When scientists from Brazil’s University of São Paulo looked at the impact of training frequency in a group of untrained young men, they found no advantage to working a muscle more often than twice a week.
The lifters were split into two groups. Both groups trained one leg five times a week using the leg extension machine. The other leg was trained either twice or three times each week.
Unlike the other studies we’ve looked at, total training volume wasn’t identical. That is, the high frequency program involved 15 sets per week, while the lower training frequencies involved 6-9 sets per week.
After eight weeks, the higher volume of training didn’t lead to muscle being built any faster. Three sets performed 2-3 times a week produced the same amount of muscle growth as three sets performed five times a week.
The researchers also noticed that the rate of progression in the high frequency leg was considerably slower than it was in the legs trained two or three times a week. The higher frequency of training seemed to impair recovery. Lifters weren’t able to add reps or weight as fast as they could on the lower frequency programs.
However, the researchers also point out that these findings are specific to untrained individuals. The results may well be different if you have a few years of training under your belt.
Here’s what they had to say on the subject:
“Given that the time course of muscle protein synthesis increase after a resistance training session changes to a more rapid and specific one, it’s reasonable to suggest that trained individuals would benefit from higher training frequencies such as five times a week. This proposal is further supported by a smaller stress impact of each resistance training session as training develops, reducing the rest period required between sessions.”
“Studies into the repeated bout effect,” explains Borge Fagerli, “show that whereas moderately advanced lifters can see a muscle protein synthesis (MPS) anabolic response for 24-48 hours after a workout before returning to baseline, advanced lifters may see the same MPS peak but the duration is shorter, on the order of 12–16 hours.”
In short, if you’re new to lifting weights, your muscles may grow just as fast whether your training is spread across one, two, or three workouts a week.
But, if you’re more advanced, you may well see better results hitting each muscle group more often than 2-3 times a week.
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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ABOUT THE AUTHORChristian Finn is a former "trainer to the trainers" and fitness writer based in Northamptonshire, England. He holds a masters degree in exercise science, and has been featured in or contributed to major media on two continents, including the BBC and Sunday Times in the U.K. and Men’s Health and Men’s Fitness in the U.S.
1. Hanssen KE, Kvamme NH, Nilsen TS, Rønnestad B, Ambjørnsen IK, Norheim F, Kadi F, Hallèn J, Drevon CA, Raastad T. (2013). The effect of strength training volume on satellite cells, myogenic regulatory factors, and growth factors. Scandinavian Journal of Medicine and Science in Sports, 23, 728-739
2. Rønnestad BR, Egeland W, Kvamme NH, Refsnes PE, Kadi F, Raastad T. (2007). Dissimilar effects of one- and three-set strength training on strength and muscle mass gains in upper and lower body in untrained subjects. Journal of Strength and Conditioning Research, 21, 157-163