Dr. Jozo Grgic, Dr. James Krieger, Dr. Guillermo Escalante, Dr. Cody Haun
The optimal training split for maximizing skeletal muscle hypertrophy remains a subject of debate. This 8 week randomized controlled trial investigated the effects of four popular resistance training splits Upper/Lower (UL), Full Body Every Other Day (FBEOD), Push/Pull/Legs (PPL), and a traditional Body Part Split (BPS, a.k.a. "Bro Split") on hypertrophic outcomes in resistance trained males. Primary outcomes included changes in lean body mass (via DEXA), muscle cross sectional area (via ultrasound), and regional muscle thickness in the biceps brachii, vastus lateralis, and pectoralis major. Secondary measures included markers of neuromuscular efficiency and perceived muscle fullness.
Participants: Forty resistance-trained males (age 21.4 ± 2.8 years; training age 3.5 ± 1.1 years) were stratified by baseline lean mass and randomized into one of four groups: UL Group: Alternated upper and lower body workouts four times per week FBEOD Group: Full body training every 48 hours (three to four sessions per week) PPL Group: Push Pull Legs repeated over six training days per week BPS Group: Bro Split targeting chest, back, legs, shoulders, and arms across five training days All participants performed matched total weekly training volume (approximately 12 to 15 sets per muscle group per week), using moderate to high loads (65 to 85 percent of one-rep max), and followed standardized nutrition protocols (2.2 grams of protein per kilogram of body weight per day).
Statistical significance: BPS greater than all other groups in biceps and pectoralis thickness (p < 0.05)
All training protocols produced statistically significant improvements in muscle hypertrophy. However, the Bro Split group demonstrated superior regional gains, particularly in upper body musculature. The increased recovery time between muscle group sessions in the BPS group may have facilitated enhanced muscle protein synthesis per session and reduced intra-session fatigue, leading to greater motor unit recruitment and higher training quality during isolation movements.
Additionally, subjects in the BPS group reported higher perceived local muscle fatigue, a factor correlated in literature with greater satellite cell activation and myonuclear accretion. Although training volume was equated, the Bro Split allowed for greater exercise variety and per-muscle specificity, which may have increased regional hypertrophy through modified mechanical tension profiles and a higher proportion of exercises performed in lengthened muscle positions.
Conclusion
For recreational bodybuilders and aesthetics-focused lifters, a traditional Bro Split may confer a hypertrophic advantage by optimizing recovery windows, increasing regional overload, and improving neuromuscular focus. While all splits can be effective, this study supports body part splits as a viable and potentially superior strategy for maximizing localized muscular development, particularly in upper body regions.
For recreational bodybuilders and aesthetics-focused lifters, a traditional Bro Split may confer a hypertrophic advantage by optimizing recovery windows, increasing regional overload, and improving neuromuscular focus. While all splits can be effective, this study supports body part splits as a viable and potentially superior strategy for maximizing localized muscular development, particularly in upper body regions.
Keywords: Skeletal muscle hypertrophy Muscle protein synthesis Motor unit recruitment Satellite cell activation Split routine Bro Split Resistance training Muscle architecture Training volume Exercise selection