It’s one of the most common questions in fitness: “How many days a week should I work out to build muscle?” You’ll hear answers ranging from three days a week to six, often delivered as rigid, one-size-fits-all prescriptions. But the truth is, there is no single magic number. The right answer for you depends on how you respond to your training.
At Pillar, we view your body as a laboratory. Your workout plan is the hypothesis, and your results are the data. This article will give you an evidence-based starting point for your experiment and teach you how to use the Pillar Methodology to find the optimal training frequency for your unique physiology. Instead of just giving you a number, we’ll give you a framework.
The Core Pillars of Muscle Growth: Stimulus & Regeneration
Before we talk about days per week, it’s crucial to understand the two-part process of muscle growth.
- The Stimulus: This is the workout itself. When you lift weights, you create microscopic tears in your muscle fibers. This damage is the signal—the catalyst—that tells your body it needs to adapt and grow stronger. This is the first of our five pillars: applying a targeted Stimulus.
- The Regeneration: This is what happens after the workout. Your body repairs the damaged muscle fibers, and to protect against future stress, it rebuilds them bigger and stronger than before. This adaptation only happens when you are resting, sleeping, and providing your body with proper nutrients. This is our third pillar: Regeneration.
Many people focus only on the Stimulus, believing more training always equals more growth. But without adequate Regeneration, you’re just breaking your body down without giving it a chance to rebuild. The goal is to find the perfect balance between the two.
Forming Your Hypothesis: What the Science Says About Training Frequency
To form a good starting hypothesis, we turn to the scientific evidence. For years, bodybuilders swore by “bro-splits,” training each muscle group just once a week. However, modern research points toward a more effective approach.
A landmark 2016 meta-analysis by Schoenfeld and colleagues found that training a muscle group twice per week produced superior hypertrophic results compared to training it once per week (1). The theory is that hitting a muscle more frequently provides more regular opportunities to stimulate muscle protein synthesis, the key process behind muscle growth.
However, a follow-up analysis in 2019 found that when the total weekly training volume (sets x reps x weight) is the same, the difference in muscle growth between training a muscle 1, 2, or 3 times per week was modest (2). This suggests that total volume is arguably the most important factor, and frequency is a tool to help you achieve that volume effectively.
The takeaway for your starting hypothesis: Aim to train each major muscle group about twice per week. This is a scientifically validated starting point for most people.
Synthesize Your Plan: Structuring Your Workout Week
The next step is to Synthesize this evidence into a practical plan that fits your life. Here are three common and effective ways to structure your week to hit each muscle group twice.
- Training 3 Days/Week: The Full-Body Split This is a highly effective and time-efficient option, especially for beginners or those with busy schedules.
- Monday: Full Body Workout
- Tuesday: Rest
- Wednesday: Full Body Workout
- Thursday: Rest
- Friday: Full Body Workout
- Saturday/Sunday: Rest
- Training 4 Days/Week: The Upper/Lower Split This split allows for more volume per session and is a favorite among intermediate lifters.
- Monday: Upper Body
- Tuesday: Lower Body
- Wednesday: Rest
- Thursday: Upper Body
- Friday: Lower Body
- Saturday/Sunday: Rest
- Training 5 Days/Week: The Push/Pull/Legs Split This is a more advanced split that allows for high volume and focus on specific muscle groups. You can arrange it to hit each muscle group roughly twice over a 5-7 day period.
- Monday: Push (Chest, Shoulders, Triceps)
- Tuesday: Pull (Back, Biceps)
- Wednesday: Legs
- Thursday: Rest
- Friday: Upper Body (A mix of Push/Pull)
- Saturday/Sunday: Rest
The Audit Protocol: Finding Your True Optimal Frequency
The scientific recommendation is your starting point, not your final destination. The most critical step in the Pillar Methodology is the Audit. This is where you analyze the data from your experiment (your training) and make intelligent adjustments.
After following your chosen split for a few weeks, ask yourself these questions:
- How is my recovery? Are you consistently sore? Is your sleep quality suffering? Do you feel mentally or physically drained? These are signs you may not be regenerating effectively, and you might need more rest days.
- Is my performance progressing? Are you able to gradually add weight to the bar, do more reps with the same weight, or improve your form? If so, your current frequency is likely effective.
- Have I hit a plateau? If your performance has stalled for a few weeks but your recovery feels great, you may have adapted to the current stimulus. This could be a sign that you’re ready to handle a bit more volume or frequency.
Based on your answers, you can refine your hypothesis. If you’re on a 3-day full-body split and feeling great, you might experiment with a 4-day upper/lower split. If you’re on a 5-day split and feel run down, you might get better results by switching to a 4-day split with an extra rest day. This is how you move from a generic plan to a personalized protocol.
Conclusion: Your Blueprint for Progress
So, how many days a week should you work out to build muscle? Start with the evidence-based hypothesis of training each muscle group twice per week, using a 3-day full-body, 4-day upper/lower, or similar split. But don’t stop there. Treat your body like a laboratory and use the Audit pillar to listen to its feedback. Pay attention to your recovery and performance to find the frequency that allows you to apply a consistent Stimulus and achieve optimal Regeneration. That is the true path to sustainable, long-term muscle growth.
Sources
- Schoenfeld, B. J., Ogborn, D., & Krieger, J. W. (2016). Effects of Resistance Training Frequency on Measures of Muscle Hypertrophy: A Systematic Review and Meta-Analysis.
- 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.