The Devil is in the Dose: Measuring Volume for Muscle Growth
~2600 words; 8-12 minute read
Key Takeaways:
Quantifying training volume is a necessary evil that allows us to effectively monitor, analyze, and modify training stress to best suit our goals.
Commonly used measurements of volume such as volume load, hard sets, and effective reps all have their own respective advantages but come with serious limitations.
While there is no perfect way to track training volume, we propose tracking “hypertrophy” and “strength” sets along with the average RPE of each category.
Humans like to quantify everything. We use numbers to measure time, income, even the difference between success and failure. Generally, thinking in this way improves our ability to construct abstract models that help to predict future events (although on an absolute scale we still, and probably always will, suck at this). Training isn’t much different in this regard. We naturally have the desire to quantify things as specifically as possible in hopes of optimizing the outcomes we’re concerned with in the long run. Training volume is the programming variable that this relationship is arguably the most evident with. We can broadly define volume as the training variable that tells us “how much” work we are doing in the gym.
To a certain degree, the obsession with properly measuring this variable is warranted. In many other areas of life, the devil is truly in the dose. Whether it be particular medications, alcohol, or even sunlight, a given amount of the substance could result in a net positive outcome while another could lead to the opposite or even death. Now, doing too many biceps curls probably won’t kill you but being able to effectively quantify how much work we’re doing in the gym will help us get closer to the “optimal” dose of the iron for muscle growth. Given that volume and hypertrophy seem to have a strong dose-response relationship (to a point), it makes sense that we persistently search for a metric that helps to explain what we observe in both the research and our experience. In this article, we’ll cover ways to quantify training volume, the pros and cons of each approach, and our suggestions on how you can best apply these methods to benefit your own training.
Volume Load:
In pretty much every exercise science textbook known to man, there will be some mention of the following way to calculate volume:
Total Volume Load = Load x Reps x Sets
On paper, this approach seems extremely pragmatic as it accounts for almost all the ways you could implement progressive overload (weight, reps, sets). Said another way, calculating volume in this way is sensitive enough to demonstrate an increase in training stress from even small deviations in workload (adding 5 lbs, 1 rep, or a set).
However, there are some serious limitations with measuring volume this way. First, we are confident that low load (~30-60% of 1RM) and high load (>60% of 1RM) training produce similar muscle growth so long as both groups train to failure and sets are equated. However, when high and low load conditions are equated for volume load, the low load groups come up short in terms of muscle growth. To illustrate why this occurs, let’s take an individual with a 500 lb squat 1RM. If they perform 30% of their 1RM (150 lbs) for 3 sets of 25 reps, that would be 11,250 lbs of volume load. If the same individual performed 3 sets of 6 reps with 85% of their 1RM (425 lbs), that would be 7,650 lbs of volume load. In order to equate the volume load of these conditions, researchers will often take a set away from the low load condition that would even things out (7,500 lbs vs 7,650 lbs). Ultimately, this ends up limiting the growth of the low load groups.
A second limitation is that volume load doesn’t account for a set’s proximity to failure. This variable seems to be particularly relevant for hypertrophy. For example, if I wanted to be the volume load king for the sake of it, I could squat an empty bar for sets of 10 throughout the day and rack up some serious numbers. However, this would clearly not be very predictive of muscle growth as there seems to be a threshold of effort a set must meet in order to be conducive for growth, although the exact distance from failure is unknown.
In summary, volume load can be an effective way to quantify training volume when exercise selection, intensity (%1RM), and proximity to failure are tightly controlled over time. Practically, however, most training programs will include different exercises, intensities, and vary proximity to failure over the course of a mesocycle making this approach less useful.
Bottom Line for Volume Load:
Useful when training variables are held pretty stagnant, struggles when comparing across different intensity ranges, exercises, and proximities to failure.
Hard Sets:
As a solution to the shortcomings related to comparing across intensities (%1RM) with volume load, counting the number of hard sets for each muscle group has been popular amongst coaches and athletes for a number of years. With this concept recently coming to light in the literature, hard sets can be defined as follows:
Hard Sets = Number of Sets of ~5-25 repetitions “to or close to failure”
This approach is, above all things, simple. Moreover, for nearly all intensity (%1RM) ranges that are efficient for muscle growth on a per-set basis (~5-25 reps per set), it’s generally effective at predicting muscle growth. We see in the research that, if the number of sets of ~5 reps or more and effort are equated, 9 times out of 10 hypertrophy is the same.
For those with primarily physique-related goals who train in mostly moderate rep ranges (~8-15 reps per set), counting volume this way is pretty tough to beat. However, there are some significant limitations when applying it more broadly. First is the ambiguity in what defines “hard.” In the research investigating muscle growth, sets are almost always taken to failure. While this serves to control effort in a research setting, we know that this isn’t necessary to maximize hypertrophy. In fact, training to failure significantly increases muscle damage, time to recovery, and potentially limits strength gains in comparison to non failure training. The next logical question is, how far from failure can we train while still maximizing muscle growth? The quick answer to this is that we don't really know, but it could be farther from failure than many think (4+ RIR). Based on many lifters’ interpretation of “hard,” sets at a 5 RPE wouldn’t count but can induce significant hypertrophy. This could lead two individuals to look at the same protocol (such as 3 sets of 8 at a 5 RPE) and come to very different conclusions when attempting to quantify the volume.
Let’s revisit our definition of a hard set: a Set of ~5-25 repetitions “to or close to failure.” It's reasonable to ask why there is a lower end cutoff of 5 reps, especially when lifters with both strength and size goals (most of our audience) include a fair amount of these sets in their programs. The answer to this question is simply a notion of efficiency. This is because sets below 5 reps don’t induce the same amount of muscle growth as moderate rep ranges on a per set basis. To demonstrate this concept, a study by Schoenfeld et al. (2014) compared 3 sets of 10RM to 7 sets of 3RM. Based on the fact that the group performing 7 sets is performing more than twice the number of sets as the other group, it's reasonable to think they would see greater growth. Maybe to no surprise, that's not what the authors found. Despite performing more than twice the number of sets than the other group, the 7 set group did not experience greater hypertrophy of the biceps. This indicates that sets below 5 reps simply aren’t as efficient for growth and thus more sets are needed to result in the same hypertrophy. To echo this point even further, a study by Klemp et al. (2016) compared a group performing 13 weekly sets of 8-12 reps per set vs. a group performing 27 weekly sets of 2-6 reps per set. Again, despite one group performing over double the sets, hypertrophy of the chest and quads were not statistically different. In concept, the goal of counting hard sets is to quantify all of the sets that maximally stimulate muscle growth. However, based on the current definition of hard sets, sets below 5 reps wouldn’t be accounted for. While it is clear these sets are not as efficient, they still can cause hypertrophy and need to be measured accordingly. This is simply a limitation of counting hard sets in this fashion that individuals need to keep in mind.
Overall, counting hard sets is really effective at predicting muscle growth when individuals train with moderate intensities. For individuals with primarily physique related goals, this is a great way to quantify volume. However, for individuals with aspirations to increase both size and strength, tracking sets below ~5 reps can be difficult with this method. Finally, defining what “hard” means in terms of proximity to failure is difficult and could differ between intensities (%1RM) to optimize muscle growth.
Bottom Line for Hard Sets:
Excellent for quantifying training volume in moderate intensity ranges, super easy to track, but struggles when sets with heavier loads and lower RPE’s are included.
Effective Reps:
To cover the gaps of the previous two methods, mainly accounting for a set’s proximity to failure and including higher intensities (%1RM), a third option has recently been proposed amongst many coaches.
Effective Reps = Counting total repetitions performed within ~5 reps of failure
(Example: 3 sets of 10 reps to failure = 15 effective reps)
A huge benefit of the effective reps model is that it can be used at any intensity (%1RM). Whether you’re performing sets of 2 at a 9 RPE or sets of 10 at a 7 RPE, effective reps calculates volume in a way that can easily be compared between protocols, which could help inform programming decisions. This seems to address the inability to include heavy loads (less than 5 reps per set) when only considering hard sets that we have previously discussed.
Additionally, counting effective reps takes into account a set’s proximity to failure. Having some sort of an effort (RPE/RIR) threshold improves this method’s predictive power. Going back to my example from earlier, If I squatted the empty bar for 30 sets of 10 throughout the day with over 10 reps in reserve on each set, I would accumulate a grand total of 0 effective reps. Contrary to counting volume load, quantifying volume via effective reps would demonstrate that training in this way isn’t great for muscle growth.
However, when we apply this framework to the literature, things become much less clear cut. In a recent study by Keitaro et al. (2020), the authors compared groups training with 7 sets of 4RM, 4 sets of 8RM, and 3 sets of 12RM. Based on the effective reps model that counts the last 5 reps from failure as “effective” these groups would be completing 56, 40, and 30 effective reps per week, respectively. Now, simply based on those numbers, we would expect that the group performing 56 effective reps would have seen the greatest muscle growth. In reality, all of these groups saw the same muscle growth of the pecs. To nail this point home, a study by Karsten et al. (2019) compared a group performing 4 sets of 10RM and another group performing 8 sets of 5 with the same load (75% of 1RM). The group performing 8 sets of 5 would have zero effective reps on most of their sets and consequently should not have even come close in the hypertrophy sites measured. However, two of the three muscles measured did not differ in muscle growth.
In conclusion, while the effective reps idea has a ton of promise in theory, actually applying this framework to predict muscle growth leaves something to be desired. Specifically, when we calculate the number of effective reps performed in multiple studies, this method of quantifying volume doesn’t seem to predict changes in muscle growth successfully.
Bottom Line for Effective Reps:
Can be successfully applied to any intensity (%1RM) range but doesn’t seem to predict changes in muscle growth when the amount of effective reps are actually calculated, likely due to the black and white cutoff of ~5 RIR.
Where Do We Go From Here?:
Now that we’ve discussed the 3 most common ways to track training volume and the advantages and disadvantages associated with each, where do we go from here? Hopefully, I’ve made clear that pretty much any attempt at tracking training volume is going to have limitations, but minimizing those limitations will allow for more accurate tracking, ultimately improving outcomes.
As far as how we can practically apply this information, I believe combining these approaches is likely the best way forward. Specifically, I think we can start by counting sets as either a “hypertrophy” or a “strength” set based on the rep range they are completed in.
Hypertrophy Sets = sets of 5 reps or more
Strength Sets = sets of 4 reps or less
Now, I know I know, you CAN produce muscle growth from pretty much any rep range, but it's not as efficient on a per set basis once you start dipping below 5 reps per set. Semantics aside, counting sets in this way clearly denotes how many of your weekly sets are truly “efficient” for muscle growth and those that are more geared towards strength. Consequently, this approach can help inform decision making when shifting the proportions of your weekly training volume. For example, let's say you’re performing 10 weekly sets, 8 of those “hypertrophy sets” and 2 of those “strength sets.” If you were looking to add exposures to high intensities in your program while maintaining volume for muscle growth, it could shift to something like this: 11 weekly sets, 7 of those “hypertrophy sets” and 4 of those “strength sets.”
Wait why did we go to 11 weekly sets, weren’t we at 10? You’re totally right, however as we've mentioned, sets below ~5 reps don’t seem to be as efficient for muscle growth on a per set basis. So, as we transfer more of our volume to low rep sets, it may be wise to increase the set count slightly to account for this. Now, I’m not saying that every hypertrophy set is exactly equal to two strength sets, but being aware of this relationship is helpful when making programming decisions.
The second variable I think is helpful to keep track of is the average RPE of each of these set classifications. As we’ve mentioned in this article a few times, the exact distance from failure to maximize muscle growth is unknown, but being in somewhat close proximity to failure is important to optimize hypertrophy (our guess is around 7 RIR). Keeping track of the average RPE of both set types will allow you to monitor how close to failure your sets are on average. As we gain more evidence on what the threshold of RIR is, coaches can slowly adapt the way they program to account for this while not having to alter the way they track volume. Additionally, this allows the opportunity to track the average RPE of heavier and lighter sets separately, which could be important because heavy loads can train farther from failure and still maximize muscle growth.
Here is an example of how we track volume at Data Driven Strength:
As you can see on the right of the image, the number of “hypertrophy” and “strength” sets are calculated along with their respective average RPEs. This allows the coach to evaluate the stimulus from each exercise and monitor changes over the course of the training cycle. Additionally, separating the two categories can be useful because the optimal proximity to failure for each set type is likely different, a topic we hope to write on soon.
Hopefully, this article has helped you conceptualize the quantification of training volume and how best to attack it. To be clear, our way of doing things is far from perfect, and I hope a better method is discovered soon. With that said, we think organizing things in this way is extremely helpful in making long term programming decisions.