Bro-splits — hitting each muscle group once a week with a brutal, high-volume session — have dominated gym culture for decades. But when researchers actually put training frequency to the test, the results tell a different story.
What the Research Found
A systematic review and meta-analysis by exercise scientists Brad Schoenfeld, Jozo Grgic, and James Krieger, published in the Journal of Sports Sciences in 2019, examined the effect of resistance training frequency on muscle hypertrophy across the available body of research. Their analysis found that training each muscle group at least twice per week produced greater muscle growth than training it only once, when total weekly training volume was equated between groups.
This builds on earlier work from the same research group showing similar advantages for higher training frequencies, and it lines up with a broader body of resistance training research: frequency alone doesn't build muscle — but higher frequency makes it easier to accumulate the volume that actually does.
Why Volume, Not Frequency, Is the Real Driver
The key detail in this research is "when volume is equated." Total weekly training volume — sets multiplied by reps multiplied by load, roughly speaking — appears to be the primary driver of hypertrophy. Frequency matters mainly because it's a more practical way to distribute that volume:
- Cramming 20 sets for chest into one session leads to significant fatigue and diminishing returns partway through.
- Splitting those same 20 sets across two sessions in the week allows for higher-quality effort on more of those sets, and more frequent stimulus for muscle protein synthesis, which rises and falls in the 24–48 hours after a session.
What This Means for Your Program
For most lifters, this research supports:
- Full-body training 3x/week, hitting every major muscle group in each session — an efficient, well-supported structure for both beginners and many intermediates.
- Upper/lower splits 4x/week, which allow slightly more volume per muscle group while still training each one twice.
- Traditional bro-splits (one muscle group per day, once per week) are not inherently wrong, but based on this research, they're a less efficient way to accumulate the same total volume compared to higher-frequency approaches.
Recovery Still Matters
Training a muscle group more often doesn't mean training it to failure every single time. Higher frequency requires managing fatigue across the week — which usually means moderating how close to failure you push individual sessions so you can still perform well and recover before hitting that muscle group again.
The Takeaway
The research doesn't support the idea that once-a-week training is optimal for muscle growth. Training each muscle group at least twice weekly, while keeping total weekly volume high and appropriately distributed, is the approach best supported by current evidence — and it's a big part of why full-body and upper/lower programs have become the default recommendation among evidence-based coaches.
References
- Schoenfeld, B. J., Grgic, J., & Krieger, J. (2019). How many times per week should a muscle be trained to maximize muscle hypertrophy? A systematic review and meta-analysis of studies examining the effects of resistance training frequency. Journal of Sports Sciences, 37(11), 1286–1295.
- Schoenfeld, B. J., et al. Resistance training frequency and skeletal muscle hypertrophy: A review of available evidence. Journal of Science and Medicine in Sport.
Discussion