Workout Quest: Why Training Muscle Groups Twice a Week is Optimal for Muscle Growth: The Science Explained

Why Training Muscle Groups Twice a Week is Optimal for Muscle Growth: The Science Explained

One of the most debated topics in the fitness industry is the frequency of muscle group training. While the traditional “bro-split” (training each muscle once a week) has been a popular choice for bodybuilders, recent research has shown that hitting each muscle group twice per week may be far more effective for achieving optimal muscle growth. This article dives into the science-backed benefits of higher frequency training, explaining why it’s a superior approach for building size and strength.

Understanding Muscle Protein Synthesis

To build muscle, one of the critical processes to understand is muscle protein synthesis (MPS). After a resistance training workout, the body initiates a period of increased protein synthesis, which lasts for about 36 to 48 hours in most individuals¹. During this time, the muscle tissue repairs itself and grows stronger. If a muscle group is only trained once per week, this growth window closes long before the muscle is stimulated again, resulting in underutilization of potential gains.

The Problem with the Once-Per-Week Routine

If a lifter follows a typical “once-a-week” training split, they are essentially only stimulating each muscle group’s growth process for 2 out of the 7 days. That leaves 5 days of unoptimized growth potential. In contrast, training a muscle group twice a week extends the time that MPS is elevated, leading to more frequent muscle-building periods throughout the week¹.

Key Findings from Recent Research

1. Brad Schoenfeld’s Meta-Analysis

Brad Schoenfeld, one of the leading researchers in hypertrophy science, conducted a meta-analysis involving 25 studies that compared various training frequencies and their impact on muscle growth. The findings were clear: training a muscle group twice per week resulted in greater hypertrophy compared to once-per-week routines².

Why is Twice a Week Better?
The primary reason is that more frequent training allows for increased muscle protein synthesis and provides more opportunities for growth. Schoenfeld’s analysis demonstrated that training a muscle group twice per week can lead to a 3.1% increase in muscle growth over a training cycle. While this might sound minimal, when compounded over months and years, it results in significantly more muscle mass.
Total Weekly Volume Matters
One key aspect Schoenfeld’s study emphasized is total weekly volume. If you equate the volume (e.g., total number of sets and reps) across training sessions, higher frequency results in better muscle activation and recovery. This means that splitting 12 sets of chest exercises into two sessions of 6 sets each is more effective than cramming all 12 sets into a single session.

2. The 2019 Review by the University of South Florida

A more recent review from the University of South Florida looked into the effects of varying training frequencies and found similar results². The researchers noted that while higher frequency (2-3x per week) promotes better hypertrophy, extremely high-frequency protocols (4+ times per week) did not yield additional benefits. In fact, training muscle groups too often can interfere with recovery, leading to joint and tendon overuse injuries.

The Takeaway: For most lifters, sticking to 2-3 times per week per muscle group is the sweet spot. Higher than that may lead to diminishing returns, especially if weekly volume is not well-managed.

Additional Support from Outlift.com’s Analysis

According to an in-depth analysis by Outlift, training a muscle group 2-4 times per week resulted in approximately 48% faster muscle growth compared to training once per week³. The reasoning behind this is straightforward: each workout stimulates MPS, and more frequent activation of this process leads to more growth opportunities.

Why Not Train More Frequently?
While high-frequency training (4-6 times per week) might seem appealing, the research shows that the law of diminishing returns quickly sets in. For most people, training each muscle more than 3 times per week does not lead to significantly greater hypertrophy and can instead cause excessive fatigue.

Why Higher Frequency Training Works: Breaking Down the Mechanisms

1. The Protein Synthesis Window

Muscle protein synthesis spikes immediately after resistance training and remains elevated for up to 48 hours¹. After this window closes, muscle protein breakdown catches up, and the net muscle gain is minimized. By training each muscle twice per week, you keep the muscle in a state of growth more consistently, leading to better cumulative results over time.

2. Increased Neuromuscular Adaptations

Another benefit of higher frequency training is enhanced neuromuscular efficiency. Training a muscle group more often improves your mind-muscle connection, leading to better muscle recruitment and force production. This means that over time, your body becomes more efficient at using the trained muscle groups, resulting in increased strength and size.

3. Lower Risk of Overtraining

Contrary to what many believe, training a muscle group more frequently (2-3x/week) can actually reduce the risk of overtraining. By spreading out the volume and intensity across multiple sessions, you avoid the excessive stress and joint fatigue that can result from trying to cram all your sets into a single day¹.

Practical Implementation: How to Structure a Twice-a-Week Training Program

If you want to implement these findings into your own routine, consider using a Push-Pull-Legs or Upper-Lower Split, which are specifically designed to target each muscle group twice a week. Here’s an example of what that might look like:

Push-Pull-Legs Routine (Twice Per Week)

Day 1: Push (Chest, Shoulders, Triceps)

Bench Press: 4 sets of 6-8 reps
Overhead Shoulder Press: 3 sets of 8-10 reps
Tricep Dips: 3 sets of 10-12 reps

Day 2: Pull (Back, Biceps)

Pull-Ups: 4 sets of 6-8 reps
Barbell Rows: 4 sets of 8-10 reps
Hammer Curls: 3 sets of 10-12 reps

Day 3: Legs

Squats: 4 sets of 6-8 reps
Romanian Deadlifts: 3 sets of 8-10 reps
Calf Raises: 4 sets of 12-15 reps

Day 4: Push (Repeat)
Day 5: Pull (Repeat)
Day 6: Legs (Repeat)
Day 7: Rest

Conclusion: Why Training Each Muscle Twice Per Week is Ideal

The latest research supports the notion that hitting each muscle group twice per week is optimal for most people aiming to build muscle and strength. By increasing the frequency of training, you allow for more consistent muscle protein synthesis, better recovery, and ultimately, greater muscle gains. If your goal is to maximize muscle growth, consider adapting your training split to incorporate higher frequency training.

References:

Built With Science. “How Often Should You Train Each Muscle To Maximize Growth?” Built With Science. ↩ ↩² ↩³ ↩⁴
Bodybuilding.com. “The Science of Training Frequency.” Bodybuilding.com. ↩ ↩²
Outlift. “How Often Should You Work Out Per Week to Build Muscle?” Outlift. ↩