Lying Leg Curls vs Seated Leg Curls
What’s the difference between seated and lying leg curls?
Is there a difference at all?
Just about every gym has one of each, and you may wonder which one you should do.
With this article, my aim is to explain the difference in less than 4 minutes.
If you have any questions left unanswered, feel free to email me at info@fitnesssimplified.org or comment below.
Don’t want to read all the details? Here’s the brief:
Seated leg curls train your hamstrings in a more stretched position than lying leg curls
Seated leg curls lead to more muscle growth, on average, than lying leg curls
You should do both over time, but it might be smart to spend most of your time on the seated leg curl machine
Quick anatomy of the hamstrings
To really understand the difference between these two exercises, we first need to understand some basic anatomy of the hamstrings.
The hamstrings are are made up of four different muscles: semitendinosus, semimembranosus, biceps femoris long head, and biceps femoris short head.
The first three muscles of this list cross both the hip and the knee joint.
This is why the hamstrings contribute to hip extension (i.e. stiff-leg deadlifts) and knee flexion (i.e. leg curls).
Flexion: the shortening of a joint angle
Here, it is the shortening of the angle behind the knee
Extension: the increasing of a joint angle
Here, it is the increasing of the angle in front of the hip
Because the biceps femoris short head ONLY crosses the knee joint, you need some sort of leg curl exercise for it to be trained at all.
However, in a leg curl motion, the other three muscles are trained differently depending on the position of your hip.
As your hip flexes more (ie knees get closer to chest), the three 2-joint muscles of the hamstrings become more stretched.
Think of the bottom of a stiff-leg deadlift.
This point of the exercise is where your hips are the most flexed, and therefore the hamstrings are the most stretched.
As your knee extends more (ie your leg straightens), all four muscles of the hamstrings become more stretched
Think of the point in a leg curl where your legs are the most straight.
It is at this point that your knees are the most extended, and therefore the hamstrings are the most stretched.
How this applies to seated and lying leg curls
Imagine you are sitting on a leg curl machine with your legs straight.
If it is a seated leg curl, then your body is in the same orientation as the bottom of a stiff-leg deadlift; meaning your hamstrings are more stretched.
If it is a lying leg curl, then your body is in the same orientation as the top of a stiff-leg deadlift; meaning your hamstrings are more shortened.
So, which one is better?
These two exercises have actually been directly compared in the research.
This study tested it in two different parts.
Part 1:
20 subjects performed seated leg curls on one of their legs and lying leg curls on the other for 12 weeks, both using 70% of their 1 repetition maximum.
The subjects performing seated leg curls gained about 5% more muscle mass than those performing the lying leg curls.
Of note, the greater increase in muscle size was only seen in the muscles that cross both the hip and the knee joint (semitendinosus, semimembranosus, and biceps femoris long head) and not the muscle that only cross the knee joint (biceps femoris long head).
Part 2:
19 of the previous subjects plus 12 more performed eccentric-only (just the lowering part) of seated or lying leg curls at 90% of their 1 repetition maximum.
The overall muscle damage was about the same between different groups.
What can you take home from this?
I think this is a clear indication to spend most of your time on the seated leg curl instead of the lying leg curl.
However, I don’t think you should spend ALL of your time on the seated leg curl.
It has been shown in some muscles that training at different muscle lengths can emphasize growth in different regions of the muscle [source].
So, you’ll most likely get your best set of hamstrings by incorporating both, just a greater amount of seated leg curls.
For instance, say you do your training in 4-week blocks.
You could do seated leg curls for two 4-week blocks in a row, and then add in lying leg curls for a 2:1 ratio.
