As far as American sports scientist Brad Schoenfeld can tell from the literature, bodybuilders and fitness fanatics make more progression by training their muscle groups twice a week than if they only train each muscle group once a week. Schoenfeld writes about this in a meta-study that has appeared in Sports Medicine.
Schoenfeld looked at abstracts of 491 studies that had compared the effect of different training frequencies. Of those 491, only 10 could be further analysed.
On the basis of the ten studies that the researchers considered good enough, the researchers concluded that the training schemes produced more muscle growth the more often per week that the subjects exercised their muscle groups.
But how many times per week should you train a muscle group for optimal results? Just twice a week? Or does three times a week give better results? The researchers did not have enough data to be able to answer this question.
The researchers drew three conclusions from the meta-study. The first is an obvious one.
“When comparing studies that investigated training muscle groups between 1 to 3 days per week on a volume-equated basis, the current body of evidence indicates that frequencies of training two times per week promote superior hypertrophic outcomes compared to one time”, they wrote. “It can therefore be inferred that the major muscle groups should be trained at least twice a week to maximize muscle growth.”
“Whether training a muscle group three times per week is superior to a twice-per-week protocol remains to be determined”, they then added. “Due to an absence of data, it is not clear whether training muscle groups more than 3 days per week might enhance the hypertrophic response.” That’s conclusion number two.
“That said, training a muscle group once a week was shown to promote robust muscular hypertrophy and remains a viable strategy for program design”, they wrote. And that’s conclusion number three.
Effects of Resistance Training Frequency on Measures of Muscle Hypertrophy: A Systematic Review and Meta-Analysis
A number of resistance training (RT) program variables can be manipulated to maximize muscular hypertrophy. One variable of primary interest in this regard is RT frequency. Frequency can refer to the number of resistance training sessions performed in a given period of time, as well as to the number of times a specific muscle group is trained over a given period of time.
We conducted a systematic review and meta-analysis to determine the effects of resistance training frequency on hypertrophic outcomes.
Studies were deemed eligible for inclusion if they met the following criteria: (1) were an experimental trial published in an English-language refereed journal; (2) directly compared different weekly resistance training frequencies in traditional dynamic exercise using coupled concentric and eccentric actions; (3) measured morphologic changes via biopsy, imaging, circumference, and/or densitometry; (4) had a minimum duration of 4 weeks; and (5) used human participants without chronic disease or injury. A total of ten studies were identified that investigated RT frequency in accordance with the criteria outlined.
Analysis using binary frequency as a predictor variable revealed a significant impact of training frequency on hypertrophy effect size (P = 0.002), with higher frequency being associated with a greater effect size than lower frequency (0.49 ± 0.08 vs. 0.30 ± 0.07, respectively). Statistical analyses of studies investigating training session frequency when groups are matched for frequency of training per muscle group could not be carried out and reliable estimates could not be generated due to inadequate sample size.
When comparing studies that investigated training muscle groups between 1 to 3 days per week on a volume-equated basis, the current body of evidence indicates that frequencies of training twice a week promote superior hypertrophic outcomes to once a week. It can therefore be inferred that the major muscle groups should be trained at least twice a week to maximize muscle growth; whether training a muscle group three times per week is superior to a twice-per-week protocol remains to be determined.