June 24, 2025, 5:01 pm | Read time: 7 minutes
Strength training is not one-size-fits-all. You can work with heavier weights and fewer repetitions and sets per exercise, or conversely, with lighter weights but more repetitions and sets. For those new to strength and muscle training, the question arises: What does the optimal training volume look like? A study now provides insights into the most effective number of training sets and found, among other things, that there can indeed be too much.
More brings more–but only up to a certain point. Those looking to build as much muscle mass or strength as possible through weight training often wonder: What number of sets per workout is truly effective? A new meta-analysis from the U.S. has examined this very question–and comes to a surprising conclusion. The researchers also found evidence of diminishing returns with very high set volumes per session. However, the optimal number depends on whether the goal is to build muscle or increase strength.
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Overview
How does training volume affect muscle growth and strength gains?
Previous studies had already found indications that higher training volume is associated with more muscle growth and strength gains–albeit with diminishing returns beyond certain thresholds. These studies had primarily focused on the volume within a training week.1,2
Researchers at Florida Atlantic University have now focused on the training volume, meaning the number of sets, of a single session. A session refers to a single workout that targets a specific muscle. The scientists sought to answer the questions: How many sets in this specific session are optimal for muscle growth or strength gains? Is there an upper limit per session beyond which additional sets provide no measurable benefit?
To do this, the researchers not only considered the number of sets completed for an exercise but also differentiated whether the muscles involved were trained directly (e.g., biceps in curls) or indirectly, also fractionally (e.g., biceps in pull-ups). This distinction is crucial for the validity of the actual load on the target muscle.
Direct vs. Fractional Set
Here’s a brief explanation of the different types of training sets:
A direct set is a training set where the trained–or in the case of this study, measured–muscle (e.g., the biceps) is clearly the main actor (primary mover) of the exercise. In other words, the muscle is specifically isolated and actively loaded as the main power source. If the goal is to enlarge the biceps, then a set of bicep curls is a direct set–because the biceps are specifically and primarily working.
In a fractional or indirect set, a muscle works but does not take the lead role. Continuing with the biceps example, pull-ups or barbell rows are fractional exercises. The biceps are engaged, but they only play a supporting role. The main mover is the back.
Study Design and Methods
The study was a systematic summary of research, which also included precise statistical comparisons (known as meta-regressions). The researchers adhered to international guidelines (PRISMA) recommended for such reviews.3
For the evaluation, only studies were considered where the training lasted at least four weeks and compared two groups with different training volumes or frequencies. Additionally, the studies had to include randomly assigned participant groups, which is considered particularly reliable.
The analysis also included only studies with healthy adults under 70 years old. They measured muscle growth (hypertrophy) using direct methods such as ultrasound, magnetic resonance imaging (MRI), or muscle biopsies. For assessing strength gains, strength tests with a maximum of ten repetitions were included. The researchers also assessed the quality of each study using a specific evaluation method (TESTEX scale).4
The per-set volume of training was evaluated as follows:
- Direct load: Exercises where the examined muscle was the focus counted fully (value = 1).
- Indirect or fractional load: If the muscle was only active in a supporting role, the training set counted as half (value = 0.5).
The main evaluations focused on which training volume was most significant for muscle growth (hypertrophy) and which for strength gains. The researchers used advanced statistical methods that considered factors such as training duration and the training status of the participants.
Number of Sets for Muscles and Strength Crucial–But There Is a Limit
The analysis provided evidence of positive dose-response relationships between the number of sets per session and both training goals examined–muscle growth and strength increase. As the number of sets increased, both hypertrophy and maximum strength improved.
However, both parameters also showed diminishing returns with increasing set volume–a classic example of the “diminishing returns” principle. This explains why training can stagnate or reach a plateau. The researchers identified the so-called PUOS (Point of Undetectable Outcome Superiority)–a model developed in previous studies to determine the point at which additional sets no longer provide measurable benefits.
- For strength gains, the PUOS was about two direct sets per session.
- For muscle growth, the PUOS was around eleven fractional sets per session.
This means: While a significantly higher set volume per session appears beneficial for muscle growth, only a few targeted sets are sufficient for strength gains. Importantly, these thresholds do not mark the absolute maximum but merely the point at which an additional set has less than a 50 percent chance of providing measurable benefits.
What about the optimal number of repetitions within a set?
This was already explained to us in a previous article by sports scientist Dr. Stephan Geisler: “It can be summarized that classic hypertrophy training (eight to twelve repetitions) is certainly an effective method for muscle building. However, since the body adapts very quickly to given loads and may then stagnate in terms of muscle growth, it would be sensible to change your training regimen more often (at least every twelve weeks) and, for example, conduct a few weeks of maximum strength training (five repetitions) or strength endurance training (20 repetitions). Because one thing is certain: Many roads lead to Rome, or rather, to muscle hypertrophy!”
What Is the Significance of the Results?
For training practice, the results mean: More sets per session generally lead to better results–but only up to a certain point. Especially in strength training, just a few targeted sets are enough to achieve most of the potential progress. However, those who specifically want to build muscle benefit from a higher volume–but only up to about eleven fractional sets per training session.
The study also highlights the importance of correctly counting training sets. If one does not distinguish between direct and indirect muscle load, training volume and effectiveness can be significantly overestimated or underestimated. For personal trainers, athletes, or health-conscious recreational athletes, the study provides a solid guide to efficiently plan training sessions.
Additionally, the analysis suggests that it is not training to the limit that is crucial, but rather the targeted stimulus in well-thought-out doses–especially depending on the training goal (muscle growth vs. strength).
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Interpretation of the Study and Possible Limitations
This meta-analysis represents one of the most differentiated studies to date on set volume per individual training session or exercise. Particularly noteworthy is the methodology, which distinguishes between direct and indirect load and relies exclusively on high-quality, direct measurement methods (e.g., MRI, ultrasound).
However, it is a preprint publication that has not yet been peer-reviewed. Even though the methodology appears solid, the final quality check by independent experts is missing. Additionally, the PUOS is based on the currently available study situation–and this includes only a few studies with extremely high set volumes. Whether very high volumes (>eleven sets per session) lead to a reversal of benefits or even negative effects cannot be determined at this time.
Another potential weakness is the heterogeneity of the included studies regarding training status, exercises, training weight used, and population. Thus, it cannot be ruled out that different training levels, light or heavy training weights, and the type of exercises influenced the study results. Moreover, due to the heterogeneous design, the transferability of the analysis to all target groups may be limited despite statistical adjustments. No conflicts of interest were reported, but the data partly comes from a parallel project by the same research group.