Chapters:
00:00 Intro
00:26 The effect of eccentric duration of barbell squats
02:21 Greater growth in the vastus lateralis of the slower tempo group?
03:01 Type I error?
04:49 Regional hypertrophy?
05:55 Greater growth with a faster eccentric tempo?
07:57 Greater strength with a slower eccentric tempo?
09:56 Conclusion
Transcript:
What is the best repetition tempo for maximum gains? Based on most influencers on YouTube I get the impression that the consensus view is: Relatively slow eccentric, meaning you lower your weights relatively slowly, the lengthening phase is performed slowly, then you do the concentric phase, the shortening phase, the lifting phase rather explosively. A new study looked at this, so let’s dig in.
The researchers specifically looked at the effect of the eccentric durations, or the lowering phase, of barbell squats. One group squatted with a 1 second eccentric tempo, and the other group squatted with a 4 seconds eccentric tempo. The load was the same, they trained the same frequency, and they trained to failure, so all else was equal. One group did more faster repetitions and the other group did fewer slower repetitions, allowing us to investigate specifically the effect of the eccentric speed on muscle hypertrophy and strength development.
An interesting little factoid about the study is that the subjects were endurance trained, but not strength trained. In fact, they were highly endurance trained. The researchers noted: “As part of their normal academic curriculum, participants engaged in 6 to 8 hours of low to high intensity exercise per week.”, but they were specifically not strength trained, so they were basically doing 6 to 8 hours of cardio per week. I don’t know for what study that’s “normal academic curriculum”, but I don’t want none of that. The main finding was that after the 7 week study, which is a little bit short, there was no significant difference in total quadriceps muscle growth between the groups.
This finding is in line with a previous 2022 review, which concluded that: “Overall, evidence supports eccentric contractions below 2 seconds duration to improve subsequent concentric performance…” So they recommend not decreasing your eccentric speed too much to improve strength development, we’ll get to the strength development of this study in a bit more detail later, and they continued: “…There is no clear difference between using eccentric tempos of 2 to 6 seconds if the aim is to increase hypertrophic response and strength.” So basically they said that if you slow your eccentric phases down a lot it might hurt strength development and it doesn’t have any effect on muscle growth.
Some research has also found that, mechanistically speaking, we get to the same level of glycogen depletion in type one and type two muscle fibers regardless of our repetition tempo, provided we get to the same endpoint. So you can do more faster repetitions or fewer slower repetitions. You get to the same level of muscular fatigue in the end and therefore the muscles are doing the same amount of work and therefore you get the same amount of muscle growth. Now in the new specific study, though, there was a curious finding because specifically for the Vastus Lateralis, the sweep of the quads, there was greater muscle growth, significantly greater muscle growth in the slower eccentric training group. Now, how do we interpret this?
What I’ve seen for most people looking at this study is that they say: “Ah! Haha! There is, in fact, greater muscle hypertrophy when we slow down our eccentrics because we get greater growth in the Vastus Lateralis.” However, there was no significantly greater growth in the total quadriceps as a whole. Moreover, none of the other four regions that were measured showed significantly greater muscle growth. So the greater growth in that one region could easily be a fluke. In statistical terms this is a Type I error.
Type I error can be thought of as a false positive. If you just test a whole bunch of different things, especially in a smaller, shorter study, then some of those things will end up being different between groups simply by chance. Like every time you do a study with measurements in every individual subject, maybe some of the subjects were just training harder, maybe some of them had better genetics, maybe some of them have different diets or something happened in the study, simply by chance there are individuals that get different results and even with randomization, sometimes more of those individuals that had results in favor of one direction or in one group and therefore you get that one group having that result. Plus you simply have measurement error, where if you do a whole bunch of measurements and every measurement, especially with ultrasound, as was used in this study, which is sensitive to the operators proficiency, if you get some bias or error there, then you can get these random flukes.
An analogy that I often see in clients is when they do a DEXA scan and they kind of obsess over the, you know, left arm versus right arm differences. Is my left arm growing versus the previous scan? And those single site measurements are simply not very accurate. The total body fat percentage estimate from the body as a whole on your DEXA scans reasonably accurate. Like it’s can still be off in a couple of percent. So even a DEXA scan is not a great way to measure your progress on an individual level. It’s good in groups, but at the individual level not so much. But if you look at individual sites, the DEXA scan is really not accurate, not even at a group level. So the difference between right arm left arm is just such a small area that DEXA scan will not be that accurate. And also with ultrasound, if you do four different measurements, then the chance of one of them being off is much greater than if you sum all of them together and you look at the total, the total is by far the most reliable. Basically, if you’re saying that there was more muscle growth, you have to explain why. Well, there wasn’t actually more total muscle growth, because if you look at the total amount of quadriceps muscle growth, it was nearly identical between the groups.
An alternative way to interpret this is that there’s regional hypertrophy. Some research indeed supports that the quadriceps has regional hypertrophy, where the eccentric face may activate the Vastus Lateralis more thereby accentuating the eccentric face might target more quad sweep versus the teardrop, the VMO near the knee. I don’t think this is a particularly strong interpretation, because research on regional differentiation in the quadriceps is very scarce. The quadriceps is a very simple muscle. It just extends the knee. That’s it. At least the Vastae muscles. So if you look at something like the hamstrings or the deltoids, yes, we see significant functional differentiation. The different muscle heads even a different functions. So you can individually train certain heads and not the other heads. But with the quads that’s not possible. Most of the myths of, you know, squatting with your knees in narrow stance, targeting the VMO, get, you know, get more teardrop with special types of squats… Those have all been debunked. So there isn’t very strong evidence for regional differentiation within the quadriceps muscles.
Still, if we’re not going by regional hypertrophy, and we’re also not assuming that this is a fluke, the study would provide some evidence in favor of slower, eccentric speeds. However, if we’re looking at regional measurements to support a case, then I can also pull up, for example, Pearson et al., which found actually greater growth with a faster eccentric tempo, which doesn’t make a lot of sense to me, because theoretically you would expect that some degree of slowing down the eccentric, or at least controlling the eccentric, should be positive because you are stronger during the eccentric. If you’re not controlling the eccentric, you’re basically just dive bombing down, then there’s essentially no eccentric muscle contraction, and you’re just completely neglecting that phase of the movement, which is actually where we can get a lot of mechanical muscle tension. But that’s all theoretical. In the end we want empirical hard data.
So in the Pearson study they looked at leg extensions performed with either a 1 seconds or a 3 seconds eccentric duration and interestingly, the 1 second eccentric duration group had greater gains in the distal quads. However, total quadricep size and strength gains were similar between groups. So again, I think it’s most important to look at these total numbers. They are the most reliable and they are the most in line with the total body of research that we have. Most research does not support much effect of repetition tempo on muscle hypertrophy. For strength development, this study had an even crazier finding because the 4 seconds eccentric group in this study actually gained significantly more strength. 1RM strength gains were greater in the squat group doing 4 second eccentrics than the group doing the 1 second eccentrics. And this directly contradicts the earlier review and a study by Shibata et al. from 2021. They looked at squats with either a 2 or a 4 second eccentric tempo, and they found that strength gains were greater with the 2 second eccentric tempo.
This makes sense because strength gains are velocity specific, and there is a thing called the stretch reflex, whereby if you lower a weight a bit more rapidly, still under control, but a bit more rapidly, you get what’s called a stretch reflex. And this is not just elastic tension like you bounce on your tendons. There’s actually also a signal being sent from the brain to the muscle when it is lengthening, especially when it is lengthening more rapidly to activate the muscle. So you get higher levels of muscle activity, active muscle tension is a little bit higher when you do a faster eccentric repetition. So mechanistically, it makes sense that a faster eccentric repetition would be better for strength development, especially if you want to be stronger with that repetition. If you have to do a very slow 1RM, then maybe it’s better to actually train at that repetition speed. It’s interesting that these studies had essentially polar opposite conclusions because they were both on squats, they were both on essentially endurance trained Individuals, because in the Shibata study they were soccer players, and they both used a relatively similar training intensity.
However, the Shibata study, the older one, they had an intensity of 75% of 1RM and in the current new study they used an intensity of 60 to 70% of 1RM. And if you look at the number of repetitions that they did here you can see that the repetitions were very high and I think this might be a reason that the faster tempo group in this study was doing essentially their reps at 15 rep max, which is very high for squats, so maybe that’s the reason that that was inferior for strength development. You actually run into issues with just cardio, you know, getting out of breath, not being as explosive. Squats don’t lend themselves particularly well to doing sets of 15 for most individuals.
So how do we interpret this new study in light of all previous research? I think a lot of people, and I see this all the time now on social media, people hyperfocus on these individual findings of individual studies, and they are like: “Oh, one study says this, one study says this, and like every new study, says something completely different.” And they’re just getting completely lost in these minor details. It’s normal and expected that every time you do a study the findings are going to differ a little bit. So if you take a little bit of a bigger picture look it’s actually very clear that most research does not find significant differences on strength development or muscle growth of the eccentric speed. If you look at some of the individual studies and also in the current new studies I do think that it is very important that you control the eccentric phase, even if simply, theoretically, mechanistically, we know that the eccentric muscle phase is where you can generate very high mechanical tension and we know that mechanical tension is the primary driver of muscle growth. So it makes perfect sense that we have to have a significant eccentric muscle contraction during every repetition.
As long as you are controlling the descent, then you’re probably fine and you don’t have to actively slow down your repetitions. As for the concentric speeds, the new study didn’t touch on that, but the short version is that for strength development – research it’s quite clear that you want an explosive concentric and for muscle growth it doesn’t matter so much. You probably want to focus on a repetition tempo that allows you to perform as many repetitions as you can. But again, most research is aligned that repetition tempo just doesn’t have much effect on your gains, so you can use whatever tempo you personally prefer. In that sense, I do recommend that people don’t count the repetitions because a 4 second eccentric duration during your squat is a hell of a long time. Try actually doing it with a metronome and you’ll see nobody does a 4 second eccentric contraction outside of these studies where there’s literally some guy timing you.
So I recommend just controlling the descent but not worrying about counting or any specific tempo and then lifting the weight either explosively if your goal is strength or just lifting it in a way that allows you to do as many reps as you can for muscle hypertrophy. Alright! I hope that helps you with your gains. If you like this type of evidence based contact I’d be honored if you like and subscribe.
