Squats vs Leg Extensions: 10-Week Study Result

Chapters:

00:00 Intro

00:13 The study

00:39 Muscle growth

01:16 Bi-articulate muscle conflict

01:53 Strength

02:39 The culprit

03:51 The data and statistical reporting

04:36 Comparison to broader literature

06:38 Outro

Transcript:

A new study found that squats absolutely crushed leg extensions when it came to quadriceps growth. Let me tell you, this raised some eyebrows in the house of Henselmans. So let’s look at the details.

The researchers had 24 untrained but recreationally active individuals perform either leg extensions or barbell back squats. The programs were matched for repetitions, training intensity, and even range of motion, which was standardized to 90 degrees. So this was essentially a very -all else equal- comparison of half squats versus relatively standard leg extensions. Most leg extension machines don’t have a lot more range of motion than 90 degrees.

After ten weeks, the average increase in muscle thickness over the three heads of the quads that were measured was 14% for the squats, versus only 4% for the leg extensions, an absolute mogging. The increase in muscle thickness was measured via ultrasound. Moreover, only squats increased muscle fascicle length and pennation angle, in line with the greater muscle growth. The extra muscle growth primarily came from the vasti heads, specifically the vastus lateralis, which is quad sweep, and the vastus medialis obliquus, which is the teardrop. There was no significant difference, although the trend was very similar, in the rectus femoris, the middle head of the quads.

The middle heads of the quads, the rectus femoris here, are particularly noteworthy because in most research leg extensions beat squats because in leg extensions you can actually fully activate the rectus femoris, whereas in squats they have a bi-articulate muscle conflict. The rectus femoris either has to contract or not contract, and if it contracts, yes, it extends the knee, but because it also crosses the hip, it basically pulls you back down, instead of allowing you to get up in a squat. You don’t want hip flexion, you want hip extension. This is consistent across EMG research, biomechanical analysis and previous analysis of muscle growth.

Squats also resulted in better strength gains. Squats increased knee extension force significantly for 14% versus 10%, and strength carryover was higher from squats to leg extensions than from leg extensions to squats. This latter finding is consistent with previous research that compound exercises transfer better to isolation exercises than vice versa, especially, or perhaps only in untrained individuals, because it also helps with general motor learning. Leg presses, for example, have been found to result in greater leg extension strength actually in some research than doing the leg extensions, which is crazy, because in trained individuals in particular, the specificity principle generally rules. The best way to get better at leg extension is to do leg extensions, just like the best way to get better at pretty much anything is to do exactly that thing.

So clearly something here was going on that made a leg extensions significantly worse than squats. And indeed, the researchers measured this and they identified a very clear culprit. This was a cam based leg extension machine, very similar to if you have a plate loaded leg extension, and the resistance peaks at the top. So in this instance with the leg extension, they got peak resistance at the most shortened muscle length. Squats, however, have basically the opposite resistance curve. In the bottom position of a half squat the resistance, or at least the difficulty of the exercise, is the highest. The actual resistance is the same, but your strength is lower, resulting in higher relative neuromuscular demands.

To the credit of the researchers, they actually measured that squats resulted in 10 to 25% higher knee extension forces because of the better match with the strength curve and the resistance curve. Therefore, I would say that this study was primarily a comparison of training with the highest forces at shortened muscle length versus the highest forces at long muscle lengths, and the results support that at long muscle lengths we get more muscle hypertrophy, consistent with many other studies that you’ve no doubt heard about over the last couple of years, with the revolution of shortened partials and training at long muscle lengths.

I would note that although the researchers went the extra mile in actually measuring forces and resistance curves and standardizing range of motion, all great things, when it came to the statistical reporting there were some yellow flags when it came to effect sizes, confidence intervals and n numbers, for example, where reporting was a little bit poor.

However, the data themselves didn’t look untrustworthy to me, with one exception potentially – the one rep max in a half squat group at the baseline, so these are recreationally active individuals, but not strength trained individuals – was 130 kilos, almost three plates. Now these were half squats and it wasn’t exactly clear how they were performed, so plausible, but on the high end if you ask me. I don’t see a lot of untrained individuals squatting almost three plates, regardless of how they do it.

It’s also very important to contextualize these findings in the broader literature. When it comes specifically to the comparison of leg extensions versus squats or leg presses, we now have three studies. This study found that squats were just better on all aspects. However, this is not the case in the other studies. In fact, research is very clear that leg extensions generally are better for the rectus femoris than squats. This means that in this particular study, it’s likely that the high tension at very short lengths, basically only getting very good muscle tension at very short lengths with a cam based leg extension, was a real detriment. In the other two studies with more conventional leg extension machines, we saw that leg presses and squats are roughly equally effective for the quadriceps.

Leg extensions are clearly better for the rectus femoris, but in both of the other studies there was also a trend for the vastus lateralis to develop more in the groups doing leg presses or squats. So this is now three studies showing that squats and leg presses are indeed better for quad sweep than leg extensions. Leg extensions almost certainly are better for the rectus femoris, but for the quad sweep, squats and leg presses seem more effective, even when you equate for the range of motion.

Now, the exact execution of leg extensions seems to matter significantly, as does the design of the machine clearly, based on this study, but overall it’s probably true that leg extensions and squats have a significant difference on which heads of the quads that they emphasize. What does not seem to matter is whether an exercise is an isolation exercise, a compound exercise, a single joint exercise, or a multi joint exercise, or whether it’s a machine exercise or a free weight exercise. This is now very clear in the literature.

All that matters is the biomechanics of an exercise. Specifically, how much tension does the exercise put on the target muscle tissue? How long is there tension and at what muscle length does the tension occur? For most muscle groups we get the most muscle growth when we expose the muscle to high tension for a significant amount of time, and the tension also occurs at long muscle lengths.

I hope this helps you optimize your training programs. If you’re interested in a customized training program using my methods, you can get a free trial to my MH Physique App with the link in the description. Moreover, if you’re interested in a more detailed analysis of biomechanics and how to optimize muscle hypertrophy, check out the link in the description to my online PT certification. See you next time!