How often should you train one muscle per week?
Can training a muscle group six times a week work better than training the same muscle group three times a week? For most people, this idea may sound completely outlandish. Training one muscle group six times a week will only ruin your joints, completely overload your CNS and leave you burnt out in a state of overtraining...
But there's fascinating research that suggests this idea might not be as crazy as you might think.
The study, known as "The Frekvensprosjektet" (Norwegian for Frequency Project), has not yet been published in any scientific journal, so it has been difficult to get important details about exactly how this study was set up. However, I was able to piece together some details with the help of the conference proceedings (3, 4), Matt Perryman's excellent book "Squat every Day" and articles by Borge Fagerli (5) and Martijn Koeveots (6).
The Norwegian Frequency Project
A group of 16 Norwegian powerlifters - 13 men and 3 women - were divided into one of two study groups. Both groups followed the exact same training program - with one key difference:
Group one trained three times a week. Group two split each training session into two sessions and performed six shorter training sessions over the course of the week. Taken together, the exercisers in both groups performed exactly the same amount of work - it was just distributed differently throughout the week. To keep the total training volume the same, the group that trained three times a week performed twice as many sets per training session.
After 15 weeks, it was the 6 days a week group that made the most progress
Strength gains in squats, deadlifts and bench presses were approximately twice as high in the 6-day group as in the 3-day group. The figure below shows the combined changes in strength for all 3 exercises. Each circle and square represents the results for one subject, while the horizontal line represents the group average.
In addition to strength measurements, the researchers also looked at changes in the thickness of the vastus lateralis (a thigh muscle) and the cross-sectional area of the quadriceps. Again, it was the 6 days per week group that built up the most muscle mass and increased the cross-sectional area of the quadriceps by 4%. Interestingly, the members of the 3 days per week group did not gain any muscle mass on average. The results can be seen in the graph below:
These results seem very strange to me. Why did so many members of the 3 days a week group lose muscle? If you look at the graph of percentage change in cross-sectional area of the quadriceps, you will see that it only shows the results of five of the eight subjects in the 3 days a week group. Where are the results of the other three? What impact would their results have had on the average of the group?
Something else that stands out is the wide range of variance in results from person to person
In terms of muscle thickness, three subjects in both groups achieved roughly the same results and saw about 5% gains. Two subjects in the 6 days per week group made substantially faster progress than all other study participants. In one of the exercisers, an increase in muscle thickness was observed that was about three times the group average.
Such a large variance in results - even among people who followed exactly the same training program - has been observed in other studies on the same topic. Some people respond extremely well to strength training. These subjects are also known as "high responders". Some will achieve "good but not excellent" results and are known as "medium responders". Others - the "low responders" - tend to make much slower progress.
This raises a question: Would the low responders in the 3 days a week group have achieved better results if they had exercised 6 days a week?
We don't know, and neither do we know whether the high responders in the 6 days per week group would have made the same gains if they had been in the 3 days per week group. In other words, it is possible that these subjects were low and high responders regardless of training frequency and that the reason for the superior gains of the 6 days per week group was that the greater number of low and medium responders happened to be assigned to the 3 days per week group.
The results of the Norwegian Frequency Project look convincing, but there are several reasons why I don't think we should immediately abandon everything we know and start training each muscle group six times a week
For one thing, the participants in this study were not overweight beginners or less physically active students, who usually serve as subjects in such studies. Instead, all of the subjects were young powerlifters with an average age of 21 and all of them had competed in national-level powerlifting competitions during the six months prior to the start of the study.
This tells us that these subjects must have been at the front of the line when the genes for "strong and muscular" were distributed. But that same set of powerlifting-friendly genes may have also made it more likely that these athletes made good progress with a program that included training six days a week.
Just as results from studies conducted with untrained beginners cannot be extrapolated to elite athletes, results from studies with elite athletes cannot always be extrapolated to those who do not have the same genetic predispositions.
In addition, muscle growth was only measured in the thigh area. We know from other studies that the quadriceps respond differently to an increase in training volume than muscles of the upper body (1, 2). The same could well apply to training frequency. In addition, there was no "mean" training frequency. Would training a muscle 4 to 5 days per week have worked as well as training 6 days per week?
Remember that the main goal of the Norwegian Frequency Project was to study strength gains. The type of training that maximizes strength gains is not necessarily the type of training that works best for building muscle.
The results of the Norwegian Frequency Project could not be replicated by other studies
In a follow-up study, researchers at the University of Florida compared two programs that included training three or six days per week (7). The subjects who participated in this study were young men in their early twenties who had been training with weights for at least 6 months. To be eligible for the study, participants had to be able to use at least 125% of their body weight for squats, 100% of their body weight for bench presses and 150% of their body weight for deadlifts. So these were not the typical untrained beginners who often serve as test subjects in such studies. However, they were very far from the level of performance of the competitive powerlifters who took part in the Norwegian Frequency Project.
The study participants were divided into two groups and trained either 3 or 6 days per week. The amount of training performed was identical for both groups, but was distributed differently throughout the week. For the men who trained three days a week, each training session lasted an average of two hours, while the men who trained six days a week each trained for one hour.
And what were the results?
This time, no significant differences in strength gains were observed between the groups. The men in the 3-day group and the men in the 6-day group achieved roughly the same results, with the researchers concluding that training frequency appears to follow the law of diminishing returns, as a high frequency of resistance training (6 days per week) compared to a lower frequency (3 days per week) does not appear to offer any additional benefits in terms of strength and muscle gain when volume and intensity are equal.
Interestingly, the high training frequency group was able to achieve faster gains in muscle mass - 2.6 kilograms compared to 1.7 kilograms in the lower frequency group.
Similar results were observed when a team of Brazilian scientists compared training a muscle group once a week with a full body workout performed 5 days a week from Monday to Friday (8). To be eligible for the study, participants had to have been training for at least three years and be able to move 150% of their body weight on squats and 100% of their body weight on bench presses.
The group that trained each muscle group once a week performed two exercises with 5 to 10 sets per exercise, while the full-body group performed 11 exercises with 1 to 2 sets per exercise. Both training sessions lasted slightly longer than 30 minutes.
Again, no significant differences in strength or mass gains were observed between the two groups - 10 to 15 sets spread over 5 days increased muscle mass and strength to a similar extent as the same number of sets performed once a week. However, similar to the University of South Florida study, the full-body group showed slightly greater gains in lean body mass compared to the group that trained each muscle group only once a week.
In another study, Croatian researchers found that training a muscle group either three or six times a week for the same volume resulted in similar gains in muscle mass and strength (9).
Beginner, intermediate or experienced exerciser?
The length of time you've been training also seems to have an impact on how your muscles respond to a higher training frequency. If you have just started training with weights, you may be able to get just as good results with a conventional training program where you train each muscle two to three times a week.
In a group of untrained beginners, training with weights one or three days a week over a period of 11 weeks resulted in very similar gains in muscle mass and strength (10). At least in terms of muscle growth, six sets once a week worked just as well as two sets three times a week.
When scientists at the University of São Paulo in Brazil looked at the influence of training frequency in a group of untrained young men, they found no benefits to training one muscle more than two days a week (11).
The exercisers were divided into two groups. Both groups trained one leg five times a week using a leg extension machine. The other leg was trained either two or three times a week. Unlike the other studies we have looked at so far, the total training volume was not identical. The high frequency program consisted of 15 sets per week, while the low frequency training consisted of 6 to 9 sets per week.
After eight weeks, the higher volume training had not resulted in faster muscle gain. Three sets of 2 to 3 days per week had produced the same muscle growth as three sets of five days per week. The scientists also observed that the rate of progression of the leg that was trained at high frequency was significantly lower than the leg that was trained two to three days per week. The exercisers were not able to increase the number of repetitions or the weight as quickly as the leg that was trained at a lower frequency.
However, the scientists also emphasized that these results are specific to untrained individuals. For exercisers with a few years of training experience, the results could be significantly different.
Here's what they had to say on the subject:
"Considering that the time course of the increase in protein synthesis after a resistance training session changes to a shorter and more specific course, it is reasonable to hypothesize that trained individuals might benefit from a higher training frequency such as five times a week. This idea is supported by a lower stress impact of each resistance training session with increasing training experience, which shortens the necessary recovery period between two training sessions."
Borge Farelli says the following:
"Studies show that even though moderately trained strength athletes experience an anabolic increase in muscle protein synthesis rate for 24 to 48 hours after a training session before muscle protein synthesis returns to baseline, this increase can be much shorter in more advanced exercisers, lasting only 12 to 16 hours."
In short, if you've just started training, your muscles can grow at the same rate regardless of whether you split your training into one, two or three sessions per week. However, if you are more advanced, you may well see better results if you train each muscle group more than two or three times a week.
Final thoughts
It's important to remember that millions of people have successfully built muscle using a wide range of different training methods. The results of the Norwegian Frequency Project should not be interpreted to mean that training every muscle group six times a week is now the official best way to train.
This research merely suggests that the range of effective training frequencies - especially for those with several years of experience training with weights - may be much wider than previously thought.
References
- 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
- 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
- http://www.ed.ac.uk/polopoly_fs/1.94449!/fileManager/Book%20of%20Abstracts%20ECSS%20Bruges%202012.pdf
- http://www.nih.no/Documents/1_SFP/ICST%202012/ICST%20Book%20of%20abstract%20Final%20291012.pdf
- http://articles.elitefts.com/training-articles/reignite-progress-with-new-science/
- http://gregnuckols.com/2014/02/18/high-frequency-training-for-a-bigger-total-research-on-highly-trained-norwegian-powerlifters
- http://journals.lww.com/nsca-jscr/Abstract/publishahead/Training_Volume,_Not_Frequency,_Indicative_of.95555.aspx
- https://www.ncbi.nlm.nih.gov/pubmed/29489727
- https://www.researchgate.net/publication/327435932_Resistance_training_frequencies_of_3_and_6_times_per_week_produce_similar_muscular_adaptations_in_resistance-trained_men
- https://www.ncbi.nlm.nih.gov/pubmed/30013480
- https://www.ncbi.nlm.nih.gov/pubmed/29852092