Yes, there is a difference between the lying and the seated leg curl, and it is at the hip, not the knee. On the seated leg curl the hip is flexed, which stretches the hamstrings at their top end while they shorten at the knee; on the lying leg curl the hip is straight. In the Zyra Workouts catalog the two rows are otherwise identical, and one training study has measured what the hip angle does over weeks.
Muscles worked
| Lying leg curl | Seated leg curl | |
|---|---|---|
| Primary | Hamstrings | Hamstrings |
| Secondary | — | — |
| Category | Isolation | Isolation |
| Equipment | Machine | Machine |
| Default rest | 60 s | 60 s |
| Step | 2 kg | 2 kg |
| Load-chart buckets | 30–120 kg | 30–120 kg |
Each working set credits 1 set to hamstrings against a 10-set weekly landmark and nothing elsewhere. Combined with the half-credits from squats, deadlifts and hinges, a leg curl is often what tips the hamstring bar over the line.
What the hip angle changes
The hamstrings cross two joints: they extend the hip and bend the knee. A leg curl bends the knee, so as you curl, the muscle shortens at the knee end. Where the hip sits decides how long the muscle is overall while it does that. Seated, the hip is flexed at roughly 90°, so the hamstrings are lengthened at the hip and never get very short even at the top of the curl. Lying, the hip is straight, so the muscle is shorter throughout and quite short at the top. The seated curl therefore trains the hamstrings at longer lengths. That is anatomy, not a measurement from our data.
Maeo and colleagues tested whether that matters. Twenty healthy adults trained one leg on the seated curl and the other on the prone (lying) curl — 5 sets of 10 at 70% of 1RM, twice a week for 12 weeks — with hamstring size measured by MRI before and after. Muscle volume increased more in the seated-trained leg, +14% versus +9% for the whole hamstrings, and the difference was in the two-joint hamstring muscles rather than the one-joint one; the authors concluded that training at long muscle lengths favoured growth1. One study, one outcome; we cite the number, not a verdict. Both machines still count identically in the app.
Setup and execution
Lying leg curl. Lie face down, hips pressed into the pad (some machines angle the pad for this), ankle pad just above the heels, knees just past the edge of the bench in line with the pivot. Curl the pad toward the glutes without lifting the hips, pause, lower under control to nearly straight.
Seated leg curl. Sit with the back against the pad, thigh pad locked down, ankle pad above the heels, knee in line with the pivot. Curl the pad under the seat as far as it goes, pause, return under control. Keep the thighs pinned; letting them lift shortens the range at the hip and changes the exercise.
Log the pin weight. Loads do not compare across the two machines — lever lengths and cams differ — so keep separate histories.
Rep and RIR targets by goal
Both are isolation exercises:
| Goal | Reps | RIR | Rep ceiling | Sets (beginner / intermediate / advanced) |
|---|---|---|---|---|
| Strength | 6–8 | 2 | 9 | 2 / 3 / 3 |
| Hypertrophy | 10–15 | 1 | 14 | 2 / 3 / 3 |
| General | 8–12 | 2 | 12 | 2 / 3 / 3 |
The rep ceiling is the number the app compares your last set against: the midpoint of the rep range plus the RIR target (round((min + max) / 2) + RIR). RIR is reps in reserve — how many more reps you could have done. These targets are the app's defaults, not a law; a program you build yourself can set anything. Notice the hypertrophy row sits one rep closer to failure (RIR 1) than the compound table — isolation rows are cheaper to take near the limit.
How progression steps on this exercise
Machines step 2 kg in the app. On the hypertrophy target (10–15 @RIR 1, ceiling 14):
| Your last set | Next recommendation | Why |
|---|---|---|
50 kg × 15 | 52 kg × 10 | Above the ceiling — add a step, reps back to the floor |
50 kg × 12 | 50 kg × 12 | Inside the range — hold and add reps |
50 kg × 9 | 48 kg × 10 | Under the floor — back off a step |
Most pin stacks move in 5 kg; take the app's direction and log the pin you actually used. Each row has an estimated 1RM page, though on an isolation machine the trend matters more than the absolute number. This is arithmetic from the progression engine, not a trial result.
Alternatives
Each curl is the other's top swap (hamstrings, isolation, machine — full marks). After that the list is short, because only four catalog rows are filed under hamstrings: the good morning and the dumbbell Romanian deadlift, both compounds. The barbell RDL and the deadlift are filed under back and will not appear — the RDL vs deadlift piece explains that quirk.
The short version
Identical rows in the app: hamstrings only, isolation, 60 s, 2 kg steps, 10–15 @RIR 1 for hypertrophy. Seated flexes the hip and works the hamstrings at longer lengths; one MRI study found more growth from it (+14% vs +9%). Do the one your gym has; do both if it has both. Educational overview only — training guidance, not medical advice.