The new science of how to maximize biceps growth

Chapters:

00:00 Intro

00:40 Incline vs Preacher curls

04:37 Study on trained women

05:27 Trained vs untrained individuals

06:43 Bayesian vs Preacher curls

07:47 My online PT Certification Course

08:12 Why does every new study seem to contradict the last one?

10:22 Should you ONLY do lengthened-biased training?

14:58 Conclusion

16:01 Outro

Transcript:

Over the past year, there has been an absolute explosion of new research on how best to train your biceps for maximum muscle hypertrophy. Traditionally, most people have trained their biceps with dumbbell and barbell curls, and in the average gym you mostly see that and occasionally some people doing some biceps curl with their elbows high up in a cable station. In contrast, most of the evidence based influencers are going all in on the lengthened bias training with exercises like Bayesian curls – my baby, Preacher curls and Incline curls. Should you go with the new hype or should you stick to the traditional exercises? Let’s find out based on the latest research.

First up – a new study by Kassiano et al. had a group of women train their biceps with either Incline curls or Preacher curls. Now, I want you to stop the video for a moment and think: Which of these exercises resulted in more biceps growth? Turns out – it depends on which area of the elbow flexors you’re measuring. Around the upper biceps Incline curls resulted in significantly more growth. However, near the lower biceps there was significantly more growth with the Preacher curls. When you do an incline curl the idea is that you stretch the biceps because the biceps is a tri-articulate muscle. It crosses not just the elbow, which most people think, but it also crosses the shoulder. So when you elevate the arm, when you raise your shoulder, like doing in a front raise, it shortens the biceps. Now, with all the research on lengthened bias training and muscles growing more when they are trained at longer muscle lengths, incline curls have become a lot more popular to train your biceps because the idea is that, well, you lengthen the biceps significantly by stretching it at the shoulder and therefore it might grow more.

Based on this study that seems to be true, at least for the upper biceps. However, the advantage of preacher curls is that in the bottom position you have very high tension. Even though the biceps is a little bit shortened, the other elbow flexors like Brachialis, and maybe even the Brachioradialis, they are not shortens because they don’t cross the shoulder. So they get maximum stimulation at a longer length and high tension. The incline curl, when your arm in the bottom position is fully vertical has the downside, just like a standard dumbbell curl, of not exposing the biceps to very high tension. It’s mostly passive at that point. So it seems to be the case that it is advantageous based on the study at least, to lengthen the biceps when training it, as in doing Incline curl. However, for the other muscle group, the other elbow flexors, the Brachialis, which in this case ultrasound cannot distinguish well between and that’s what they used, is likely to grow more from doing a Preacher curl, because you get the benefits of training at long length and having a lot of tension in the lengthened position.

Many people overly focus on just exposing the muscles to long muscle lengths, but you also want high tension at those long muscle lengths. Otherwise, there is still not a lot of tension in the position, and ultimately tension is the driver of muscle growth. We know from tons of research that muscle growth is principally, perhaps exclusively, driven by mechanical tension. This hypothesis that the extra growth in the lower elbow flexors in this study using ultrasound comes specifically from the brachialis and not from the biceps is supported by another, yet to be published Japanese study.

This new Japanese study is not yet published so we don’t have the full text and it has not been peer reviewed, so take these findings as preliminary, but based on what we know from the conference proceedings, the researchers compared in the same individuals – in men doing dumbbell curls as either incline curls or as preacher curls, so a very similar setup to the previous study, with 50 degrees shoulder flexion for the preacher curls and 50 degrees, it seems, like, a shoulder extension for the incline curls. So it’s a very inclined curl where you’re sitting way back and you get a lot of stretch on the biceps. And they used MRI which is more sensitive than ultrasound and they specifically measured growth in the brachialis, the brachioradialis and the biceps brachii. The researchers found that for the elbow flexors as a whole there were no significant differences between the groups. However, for the biceps specifically, the incline curls resulted in significantly more growth, and this was most pronounced in the top part of the biceps, exactly in line with the other new study.

When looking at the brachialis and the brachioradialis, the researchers found that the preacher curls resulted in significantly more growth. So this study supports that preacher curls, by virtue of putting high tension at long muscle lengths of the brachialis and the brachioradialis result in the greatest growth in those muscles, whereas incline curls do achieve what they are meant to achieve with stretching the biceps, which is growing the biceps more. But because there’s still not a lot of tension at the bottom position, it’s not ideal for the brachialis and the brachioradialis.

Now, both of these studies were on untrained individuals, but another study on strength trained women found a similar trend. The researchers again compared preacher curls to incline curls. I don’t know why they keep doing this and not just look at a normal curl or like a standard dumbbell or barbell curl first, but this is the research we have. And they found, just like the previous research, that in total elbow flexor muscle volume, based on ultrasounds, there were no significant differences between the groups. However, when specifically looking at growth near the elbow, the preacher curls resulted in significant muscle growth, whereas the incline curls did not. So this study aligns with the general trend that you get more growth near the elbow with preacher curls, and you get probably more growth near the top, closer to the shoulder with inclining curls. However, in this case, the differences were not, strictly speaking, statistically significant between the conditions.

Most people think that research is always better when it is on trained individuals, and I also like research on trained individuals when trying to extrapolate the results to trained individuals. But you have to take into account that in trained individuals it’s much harder to find significant effects. I’m already surprised when we find the significant effect to begin with, because if you have people that have been lifting for years and you have them do eight weeks of strength training, how much growth are you really expecting to find? Mainly I’m surprised that there’s significant growth to begin with.

So when you’re looking at a small effect in one group and a small effect in the other group, and you’re trying to determine whether one of these small differences is bigger than the other small difference, it’s just very difficult. And that’s why untrained individuals actually are a lot better to study often in these cases where you have the issue that maybe you cannot extrapolate the results to trained individuals, but in the vast majority of cases you can, and it is much easier to demonstrate significant differences between groups, rather than just expecting to find no differences between the groups in terms of statistical significance the vast majority of the time because you’re looking at such small differences.

Now, that does mean that we are looking at small differences here, so we are really talking about optimization and fine tuning of your biceps training. In the end, these things are clearly not as important as just training hard and getting your volume in. I think nobody disputes that, but it’s good to emphasize it.

And speaking of null findings, we have another new study from Iran that is also not yet published, so again, the findings are a little bit preliminary. But from what I know, the researchers compared Bayesian curls (my baby) to preacher curls, and they found no significant differences between the groups.

However, when looking at the general trend in absolute terms, the Bayesian curls were better for biceps growth, whereas the preacher curls were better for brachialis growth. So while these differences were not statistically significant in this 10 week study on 15 individuals, the findings are in line with the overall trends in the research at this point. And again emphasizing that we are looking at small effects here, not massive differences. And that brings us to the last two new studies on how to train your biceps. One of them is hardly worth mentioning, I think. They again looked at preacher curls and incline curls and found no significant difference this time between two groups, but it was a three week study, for some reason using blood flow restriction. So I wouldn’t put a whole lot of stock into this study specifically. Other than maybe to emphasize that again, you cannot expect this level of fine tuning to make massive differences in your gains over a 3 week period. And if you were expecting that, you are probably on the wrong fitness channel. And this also brings me to a note in general about how to interpret research and how to put these findings into practice.

I see a lot of people on social media get confused with research seemingly flip flopping and contradicting itself from one study to the next. If you look at the trend of all of these studies, you could think of this as: “Preacher curls are better!” – “No, preacher curls are not better.” – “Preacher curls are better.” Why does research keep contradicting itself?

That is not how you should interpret research. Every new study leans towards the null in terms of results, so you generally expect not to find a significant difference because we have relatively short studies with relatively few individuals, and especially when we’re looking at trained individuals, we’re also looking at very small differences in muscle growth to begin with. So it’s very difficult to find a significant between group difference. And what you should do is not take the results exactly at face value, especially not just looking at the significance level. What you should do is look at the total body of research as a whole and look at the trend. And the trend here is clearly that lengthened bias training tends to be superior. And we see a general trend specifically for having high tension at a long muscle length for the biceps to result in more growth in the brachialis and possibly the brachioradialis. Whereas incline curls may be very good for the biceps, especially the upper part due to stretching the biceps very much.

You might get the best results with something like a Bayesian curl where you not only have long muscle lengths, but also high tension in the bottom position. Some of these studies are not statistically significant, but there are no studies finding the opposite. So you’re looking at a trend where either you have benefits or the effects are neutral. Even purely from that basis you can say- just statistically you you should place your bets on lengthened bias training in the sense. So it’s not so much the case that research is contradicting itself. It’s simply that we are looking at, say, a number here and research fluctuates around what number they find specifically, but the real number is in between. And it’s clear that the number is here and not here.

There are no studies finding that Bayesian curls are worse than dumbbell curls, for example. That would really be research flip flopping. It’s just the case that when you compare the results of individual studies to the overall trend you can expect many of them to result in no significant differences, whereas if some studies find benefits and no studies find detrimental effects, that is probably a training technique you want to implement.

Now, does this mean you should only do lengthened bias training and you should never do exercises that train the biceps at shorter muscle lengths? For the biceps specifically, this actually does make some sense because we know that the biceps benefits from being trained at longer lengths both in active and passive tension. Some muscles, they become a lot weaker when you train them at longer muscle lengths, but the length tension relationship of the biceps is such that it’s actually the strongest near anatomical position when your elbow is at your side and the arm is already fully extended. So the biceps is relatively strong in terms of active tension and then it also gets more passive tension when you stretch it, meaning that you basically get the best of both worlds. Maybe at least up to the point that you stretch the biceps enormously with an inline curl, but especially for a Bayesian curl there is no reason to believe that a standard dumbbell curl could be superior to a Bayesian curl. So purely theoretically, Bayesian curls should just be better than standard dumbbell curls. And research generally also again leans in favor of lengthened bias training with no results finding benefits for shortened length training.

However, all of these studies so far have looked at individual exercise comparisons. We also have a great new study looking at what happens if you go all in on the lengthened bias train, you only do lengthened bias training, versus what if you do half your training with a lengthened bias and the other half training at the shorter muscle lengths? Do you get better results from the variety, or is it better to really go all in on the lengthened bias training?

This new study by Hinson et al. is a preprint, so it has not yet been peer reviewed and the findings should be regarded as preliminary, but I don’t expect major changes because all the data have already been published and I don’t see any glaring issues with it. This study had a very strong design because it had trained individuals perform an eight week training block two times. One time they did 12 sets of incline cable curls. I guess these are actually technically seated Bayesian curls. And the other time they did six sets of these seated Bayesian curls, or incline cable curls, and six sets of kind of Scott cable curls, I guess. Well, one of them was in a shortened position and one of them was with the biceps very lengthened. So is it beneficial to train your biceps with just 100% lengthened bias training, essentially doing nothing but Bayesian curls, or is it better to have some exercise variety with half your volume at shorter lengths and the other half at long muscle lengths?

Overall, the researchers concluded that the differences in gains were not meaningfully different, suggesting that it’s fine to do half your training at shorter muscle lengths. There might be some benefits to some exercise variety and at least it’s not necessary to go all in on the lengthened bias train. However, when looking specifically at the results, I would definitely rather have the gains of the Bayesian curls in this study. Especially because the Bayesian group didn’t benefit from any exercise variety. They don’t need to do a Scott curl with your elbows way high up to really shorten the biceps to have exercise variety. You can have the exercise variety with, say, like the other studies did, incline curls and preacher curls or a lean back Scott curl. Something like that. I would say that the results trended in favor of the Bayesian curls because while the muscle thickness changes were virtually identical between the groups, when looking at muscle cross-sectional area, it increased 89% more after the long length program with an 81% probability of being superior.

Moreover, arm circumference, even though it’s a crude measure, increased reliably more in the Bayesian curl group. And isometric bicep strength, which is a measure of strength, not hypertrophy, but it correlates very well with size because it’s a measure of very crude strength, very raw strength that’s not technique dependent, also increased marginally more in the long length group. So overall, I would say the results did trend considerably in favor of a long length group, especially again, considering that this is a short study in trained lifters without any exercise variety in the Bayesian curl group.

So with that in mind, I would say- yes, these are actually somewhat meaningful increases in muscle growth that over the long run might be very considerable. And knowing that there is zero trends in research at all of any benefits of training the biceps at a shorter muscle lengths and also, theoretically, there are no benefits because when you shorten the biceps significantly, when you do any exercise with the elbows not that your side, but your elbows forward, then you are reducing both passive and active tension on the biceps. So there’s just no theoretical or empirical rationale to train the biceps at short lengths.

The biceps is also a relatively short muscle with most of the fibers spanning the entire length of the muscle. Therefore, regional hypertrophy is not very expected, and it’s unlikely that you need a ton of exercise variety. Any benefits from exercise variety you can get with multiple exercises that still all bias the biceps to being trained at longer lengths, either with higher tension or with longer muscle lengths. It’s also worth noting that muscle soreness and workout perceived effort ratings did not differ between groups, so there was also no evidence of the stimulus to fatigue ratio being worse for only training at long muscle lengths.

So all in all, I would say based on the research, that it actually makes sense to go pretty much all in on the long length training specifically for your biceps, at least because of the theoretical and the empirical evidence that the biceps benefits greatly from being trained at long muscle lengths. You get higher active tension, you get higher passive tension, and all the studies lean either in favor of benefits for training at long lengths, or at worst, you get the same gains as with other exercises and you don’t lose out on anything. And for exercise variety specifically, it seems that preacher curls are very effective to train the brachialis, which may help you get that muscle in between the biceps and the triceps being more visible. And also for the brachioradialis there might be benefits of doing preacher curls and exercises that really hammer the biceps with lots of tension, you have very high tension when the arm is fully stretched out. For the biceps inclined curls, Bayesian curls with the elbow even behind the body seems to be particularly effective. So having exercises mostly between those two categories seems to be the best bet without any downsides to maximize your biceps growth.

All right. I hope this helps you build bigger guns. If you like this type of evidence based content, I’d be honored if you like and subscribe.