Many people don’t determine training volume individually for each muscle group. Some people come close with the shortcut of pushing vs. pulling exercises, but this categorization breaks down for rotary exercises like pec flys, which are neither a pull nor a fly, and exercises like barbell hack squats, which are technically a pull but train muscles commonly associated with pressing (i.e. the quads). They also don’t take into account important biomechanical differences between seemingly similar presses or pulls, like dumbbell presses not activating the triceps as much as barbells for presses due to the more open kinetic chain. As a result of not optimizing training volume for each muscle individually, many common training programs like Starting Strength or 5×5 are woefully imbalanced in terms of volume per muscle group.
With the new training volume research over the past year, people have started paying more attention to how to count training volume. This begs the question: when determining your training volume for each muscle, should it be the same for all muscles or do certain muscles require more volume than others for maximum growth?
Training small vs. large muscles: the theory
There are several reasons why you’d want to give different muscle groups more volume than others, notably how important the muscle is to you and its training advancement. In this article I’ll focus on 1 specific factor: the muscle’s size. There are many theories about how muscle size influences training volume and frequency, but they’re mostly speculative at this point:
- Training large muscle groups may theoretically induce more central nervous system fatigue, therefore lowering the optimal training frequency, but as I’ve previously shown, CNS fatigue is overrated.
- Training large muscle groups may eat up more central recovery resources, therefore warranting a lower volume or training frequency. However, I don’t see which central resources would be a factor here. Metabolic factors like oxygen and blood flow should all recover within a matter of minutes, so they shouldn’t influence training frequency.
- Small muscle groups should have fewer muscle fibers with less functional compartmentalization, so they may need less volume to stimulate all muscle fibers. This makes perfect sense to me, but the number of muscle functions and its size don’t correlate perfectly. For example, the quads are huge but relatively simple in structure, whereas the hamstrings are smaller (data below) yet much more compartmentalized.
What I haven’t seen anywhere is a comprehensive analysis of the data to see which theories are right. So let’s look at the facts, but before we do that, we must first categorize which muscles are small and which are large, because most people’s idea of this is purely based on the muscles’ outer appearance. Judging a muscle’s size based on how big it looks from the outside is highly biased, because you can’t see how far inward the muscle goes. It’s like trying to guess how many square feet a house is by only looking at the front entrance.
For example, many people think the lats are a large muscle group, because they cover a large surface area, but their total muscle volume is relatively small, because they’re a relatively thin sheet of muscle. The calves, on the other hand, are generally seen as a small muscle group, but they’re actually very large, because they cover much of the inside of our lower leg, not just the bit you see on the surface.
Which muscles are large and which are small?
My research team has compiled the data from all studies we could find that measured or estimated muscle volume in various muscles of the human body. These data are in untrained individuals to exclude confounding the measures by training experience. Obviously, more trained muscles would otherwise tend to be larger than lesser trained muscles. Many studies are done on corpses, as live human subjects are often reluctant to undergo dissection. The most relevant studies are Holzbauer et al. (2007), Lube et al. (2016), Garner & Pandy (2003), Wood et al. (1989), Veeger et al. (1991), Bassett et al. (1990), Winters & Stark (1988), An et al. (1981), Veegers et al. (1997) and Cutts et al. (1991).
Most measurements agree well with each other. In the following images we show the weighted average muscle volume of each major muscle group for men and women. Some studies only reported mixed gender measurements. We grouped these with the male data, because – perhaps surprisingly – the ratio of the size of different muscles appears to be roughly the same in men and women. The reason women seemingly have thicker lower bodies and more booty appears to mostly be because they store more fat there, not because these muscles are more developed.
The data paint a much different picture than many people intuitively guess:
1. The quads are by far the biggest muscle group in the body, both in men and women. They’re roughly twice as large as the runner-up.
2. The next biggest muscle group is a tie between the gluteus maximus and the calves. Yes, the calves are huge. However, this may be in part because the calves in untrained individuals are already relatively more developed than other muscles, as they’re used whenever you’re on your feet and the soleus muscle is extremely slow-twitch dominant, so it responds quite well to endurance training. So in trained individuals the calves probably fall somewhat. Plus, when including the glute medius and minimus, the glutes are much bigger, so we can say the glutes are second largest and the calves come third.
3. Then close after we have the hamstrings, before we get to the upper body, which has far smaller muscle groups than the lower body.
4. The delts are the largest upper body muscle group. The biceps is by far the smallest. In between them most muscles are roughly the same size, including the traps, pecs, triceps and lats.
Now that have a classification of small vs. large muscles, let’s see what the data say about how we should train these muscles.
Training large vs. small muscles: volume
One way to investigate if we should train small and large muscles differently is to see how they react to changes in training volume. Do certain muscles benefit more from higher volumes than others? We have 13 studies that measured the effect of different training volumes on different muscles while keeping training frequency and other program variables constant: Barbalho et al. (2018), Schoenfeld et al. (2018), Ostrowski et al. (1997), Radaelli et al. (2015), Amirthalingam et al. (2017), Ronnestad et al. (2007), Bottaro et al. (2011), Radaelli et al. (2013), Radaelli et al. (2014), Rhea et al. (2002), Barbalho et al. (2019), Hackett et al. (2018) and McBride et al. (2003).
The most studied muscles by far are the biceps, the triceps and the quads, because limb muscle size is much easier to measure than torso muscle size, but we also have data on the chest, glutes and hamstrings and 2 studies that allow us to compare the whole arms vs. the whole legs.
In 11 of these 13 studies, all muscles responded the same way to a change in training volume: there was no significant difference in the effect of training volume on muscle growth. Whether training volume significantly enhanced, decreased or did not affect muscle growth, this effect did not differ depending on the size of the different muscles measured. This was true for 9 out of the 13 studies even when just taking the raw percentage muscle growth values and not just considering statistical significance: the maximum muscle growth values were all in the same volume group in these studies. This similar response to training volume strongly suggests large and small muscles should be trained with the same volume.
However, if we look at the 4 studies that didn’t find a completely uniform effect of training volume on muscle growth between different muscles, 3 of them support somewhat of a trend.
1. The first study’s probably not useful to look at. In Amirthalingam et al. (2017)’s German Volume Training study, the triceps and the hamstrings grew almost twice as fast on the higher volume, whereas the quads and the biceps grew over twice as fast on the lower training volume. Training volume was not balanced equally between muscles in this study and training volume was only altered on the primary movements. Since training volume normally has an optimum U-shape relation with training volume – more is better up to a point, after which it starts becoming detrimental – this study doesn’t allow us to fairly compare the effect of training volume on these muscles.
For what it’s worth, the biceps and the quads had the same optimum volume and these are the smallest and the largest muscles in the body, so these data don’t support any effect of a muscle’s size on its optimum training volume.
2. The most interesting outlier is Radaelli et al. (2014). In this study, the quads grew faster in the higher volume group (17% vs. 13%), whereas the biceps did not: it grew non-significantly slower in the higher volume group in fact: 15% vs. 16%. ‘High volume’ was 3 sets per exercise twice per week and the participants were untrained older women, so it’s possible the quads responded better to higher volume as they were less detrained. This study isn’t the strongest evidence, but it was properly controlled and lasted 20 weeks, so this finding provides some support that the biceps has a lower optimum training volume than the quads.
3. In Bottaro et al. (2011), training volume did not significantly affect muscle growth in untrained men. While not statistically significant, the lower volume quad group lost 2.9% muscle (they did only 2 sets per week, but it’s still an impressive feat to lose muscle as an untrained individual…), whereas the higher volume quad group gained 2.5% muscle. The biceps showed the opposite pattern with 7.2% growth in the 1-set group and 5.9% growth in the 3-set group. Thus, this study weakly supports Radaelli et al. (2014) that the quads may have a higher optimal training volume than the biceps.
4. In McBride et al. (2003), again untrained men and women somehow managed to make zero gains over a 12-week study. This is why you should be skeptical of low volume proponents citing research like this: these subjects were evidently pussyfooting around. Arm and leg lean mass did not significantly increase regardless of whether the participants were in the 1-set or the 6-set group. And when I say zero gains, I mean it. The muscle growth rate was 0% for the lower volume groups in both muscles. However, the only muscle growth that occurred was for the 6-set group in the quads: 5.1%. So again we have some evidence in favor of a higher optimal volume for the quads, even in individuals with less of a spine than a jellyfish.
Are these 3 studies enough to make a trend? Below we plotted the average muscle growth rates of all the studies in the 3 most studied muscles – the quads, triceps and biceps – for the lowest and highest volume groups of each study. There does appear to be a trend. On average, the quads and triceps gain more muscle when you train them with more volume, yet the biceps growth rate decreased on average with higher training volumes.
The poor response of the biceps to higher volumes is unlikely to be the result of its size, because the triceps responds nearly identically to the quads despite a huge size difference. Moreover, all available data from individual studies on the chest, glutes and hamstrings supports that these muscles respond the same way to different training volumes even though they vary majorly in size (the pecs are tiny compared to lower body muscles). We also have a substantial literature on the effect of adding arm isolation work to compound exercises. This literature generally finds no to small improvements in muscle growth from the addition of arm isolation work, particularly for the biceps. Notably, Gentil et al. (2013) found that adding 6 sets per week of biceps isolation work to 6 sets of pulldowns did not significantly increase elbow flexor muscle thickness. The overall literature average effect sizes do support a benefit of arm isolation work to compound work, but it’s smaller and more inconsistent than you typically hear. This might be in part due to an inherently poor response of the biceps to higher volumes.
In sum, 10 out of 13 studies support we should train all muscles with the same volume. 1 Study found the biceps has a lower optimal volume than the quads and 2 more studies non-significantly trend in this same direction. When averaging all study results, it appears that the biceps respond more poorly to higher training volumes than the quads and the triceps. Research on the addition of biceps isolation work to compound exercises also finds only weak benefits. The chest, hamstrings and glutes respond similarly to training volume as the triceps and the quads, so the biceps seems to be the outlier rather than small muscles in general.
Training large vs. small muscles: frequency
We can do the same analysis with training frequency. Some people argue smaller muscles recover faster due to requiring fewer recovery resources, though it’s unclear to me what resources those would be exactly, as factors like blood flow shouldn’t be the limiting factor of recovery between workouts.
We have 5 studies that measured the effect of different training frequencies on muscle growth while keeping all other program variables constant, including set and total work volume: Saric et al. (2018), Schoenfeld et al. (2015), Yue et al. (2018), Arazi & Asadi et al. (2011) and Lasevicius et al. (2019).
In all of these studies, the biceps, triceps and the quads responded the same way to different frequencies and in 4 out of 5 studies, maximum muscle growth occurred in the same frequency group even without taking into account statistical significance. Saric et al. (2018) is the only near-exception: the quads responded non-significantly better to the higher training frequency than the biceps and the triceps. Moreover, the biceps only gained a significant amount of muscle with the lower frequency. So this study provides weak evidence that the quads respond better to higher training frequencies than the biceps.
To look at if there’s any overall trend to support that we should train the quads more often than the biceps, we’ve plotted the average muscle growth for the 3 muscles in the low vs. high frequency groups below. The lines all run in roughly the same direction, indicating the effect of training frequency is similar for all muscles. However, it does appear the quads respond a bit better than the triceps and the biceps to being trained more often.
Interestingly, the overall trend is downward, suggesting higher frequencies with the same total training tonnage may be detrimental. So should we train with lower frequencies?
Probably not, because outside the lab you’re not in a tonnage-equated setting. Keeping tonnage the same is only possible normally if the subjects are training submaximally. If you spread out your exercises or sets across more sessions, you should be able to do more reps. I’ve harped on this many times before on my site and social media study reviews, so I’ll explain it only briefly again with an example: when can you do more total reps on the bench press at 80% of 1RM: when you do 10 sets on Monday (national bench press day) or when you do 5 sets on Monday and 5 sets on Thursday?
If you answered 10 sets on Monday, do you even lift?
Spreading out your work across the week reduces the negative effect of fatigue on performance, thereby allowing you to lift heavier weights or do more reps with the same weight. Thus, higher frequencies in practical settings normally increase total training tonnage (sets x reps x weight). Let’s look at the effect of training frequency when we keep the number of sets the same but tonnage increased. We have 5 studies that fit these criteria and measured multiple muscles: Zaroni et al. (2018), Ferrari et al. (2013), Izquierdo et al. (2005), Gomes et al. (2018) and Brigatto et al. (2018).
In contrast to the tonnage-equated studies, in these more natural settings the average muscle growth rates were highest for the higher frequency groups for all muscles: the biceps (6.5% vs. 4.6%), the triceps (8.5% vs. 5.7%) as well as the quads (10.5% vs. 8.1%), see the graph below. This supports a potential benefit to higher training frequencies that’s mediated by increased training volume. I’ve discussed that many times before on my site and social media, so I won’t go into that again further here.
Back to the topic of this article: these data support that muscle size does not influence the response to training frequency. Big and small muscles respond the same way to different training frequencies in these data.
Most of the 5 individual studies support the overall trend. The overall trend supports that all 3 muscles obtain the same benefit from being trained more often: more work and therefore more growth. 2 of the 5 studies support this completely: the effect of training frequency was the same for all muscles and all muscles achieved maximum muscle growth in the same group.
We also have a study by Stec et al. (2017) that studied the effect of different training frequencies without keeping set volume the same. The thighs and arms both responded better to higher frequency-volumes.
In the remaining 3 studies by Brigatto et al. (2018), Gomes et al. (2018) and Ferrari et al. (2013), there was no statistically significant difference in muscle growth between the low and high training frequency. Brigatto et al. found that the biceps achieved non-significantly more growth in the low frequency group, in contrast to the triceps and quads. Ferrari et al. also found the biceps achieved most growth in the low frequency group, in contrast to the quads. However, Gomes et al. found the arms achieved better results in the high frequency group, whereas the legs achieved better growth in the low frequency group.
You could say based on these individual study results that there’s again a very weak trend here to support that the biceps have less to gain from being trained more often than the triceps and the quads do. However, it completely balances out on average and none of the studies found a statistically significant difference in the response of these muscles to training frequency.
Overall, the data show that all muscles respond similarly to training volume and training frequency. More training volume is generally better up to a point that depends on recovery capacity. Higher training frequencies can be beneficial but normally only if they result in a higher total weekly training tonnage. Thus, we can probably train all muscles the same way, given that they’re equally developed, you prioritize them equally etc. The relative size of different muscles doesn’t appear to influence how they should be trained. In fact, most theories based on relative muscle size don’t correctly categorize muscles as big or small to begin with. For example, the delts are commonly called a small muscle group, yet they’re objectively the largest major upper body muscle group. Likewise, the calves are commonly called a small muscle group, yet they’re in fact one of the largest muscle groups in the whole body.
However, there is a trend for the biceps to respond more poorly to higher training frequencies and especially training volumes than the quads. This is not likely due to the size of these muscles though, because the triceps responds similarly to the quads while being much closer in size to the biceps than the quads. Plus, all available evidence for the chest, glutes and hamstrings supports they can be trained the same way as other muscles, despite having very different relative sizes. So there may be something unique about the biceps that makes it not gain much from being trained more. Until we have more research and a plausible mechanism to explain this, I wouldn’t make radical changes to your biceps training, but at least the data firmly support that we shouldn’t train the biceps more than other muscles.
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