The leg press and the hack squat are two machines that do the same basic job — load a knee bend while the trunk is held still — and the Zyra Workouts catalog files both under quads as compound machine exercises with 150 s default rest. The differences are the body position (seated and pushing, or standing and squatting), the secondary muscles the catalog credits, and what your feet can do on the plate. The leg extension sits beside them as the isolation option.
Muscles worked
| Leg press | Hack squat | Leg extension | |
|---|---|---|---|
| Primary | Quads | Quads | Quads |
| Secondary | Glutes, hamstrings | Glutes | — |
| Category | Compound | Compound | Isolation |
| Equipment | Machine | Machine | Machine |
| Default rest | 150 s | 150 s | 60 s |
| Step | 2 kg | 2 kg | 2 kg |
| Load-chart buckets | 80–280 kg | 80–280 kg | 30–120 kg |
Every working set of either sled credits 1 set to quads and 0.5 to each listed secondary; the leg extension credits quads only. Whether the hamstrings "should" be on the hack squat row is a fair question — the catalog says no, and that is what the volume count uses.
What the machine changes
On a leg press you sit with the back against a pad and push a sled away along a rail, usually at 45°. Your hips are already flexed at the start, and the range is decided by how far you let the sled come down. Feet high and wide bring the hips through more range (more glute and hamstring involvement — the reason the catalog lists them); feet low keep the knees travelling further and the quads doing more.
On a hack squat you stand on the plate with your back and shoulders against pads and squat the sled down and up. The trunk cannot lean forward, so the knees must travel forward to get depth — a mechanically quad-biased squat. Feet forward on the plate lengthens the knee travel further; feet under you shorten it.
In plain terms: both take balance and trunk position out of the lift so the knee extensors can be loaded directly; the leg press starts you folded at the hip, the hack squat starts you standing. This is mechanics, not a trial result — we have no EMG source to cite, so we do not cite one.
Setup and execution
Leg press. Set the seat so the knees bend past 90° without the hips rolling off the pad. Feet shoulder width, mid-plate unless you are deliberately shifting emphasis. Lower under control until the hips are about to lift, then press without locking the knees hard at the top. Log the plate load you put on the sled (the number the machine's plates add up to); the empty sled is not counted.
Hack squat. Shoulders under the pads, feet slightly forward, brace, release the handles. Lower until the thighs are at least parallel to the plate, then drive up. Same footing every set.
Leg extension. Pad on the lower shin, knee joint in line with the machine's pivot, extend to straight and lower under control. The pin weight is what you log.
Rep and RIR targets by goal
The two sleds are compound exercises:
| Goal | Reps | RIR | Rep ceiling | Sets (beginner / intermediate / advanced) |
|---|---|---|---|---|
| Strength | 3–5 | 2 | 6 | 3 / 4 / 5 |
| Hypertrophy | 6–10 | 2 | 10 | 2 / 3 / 4 |
| General | 8–12 | 2 | 12 | 2 / 3 / 4 |
The leg extension is an isolation exercise and gets the isolation table — higher reps, and one rep closer to failure on the hypertrophy target:
| 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.
How progression steps on this exercise
All three are machines, so the app steps them by a fixed 2 kg. Real machines rarely do: a plate-loaded sled moves in whatever plates you have, a pin stack in 5 kg or so. The recommendation is still useful as a direction — it tells you to go up, hold or come down — and you log what the machine actually allowed. Example on the leg press, hypertrophy target (ceiling 10): 200 kg × 11 → 202 kg × 6 recommended; load 205 kg if that is the next plate and log 205. Each row has its own 1RM page and load chart. This is arithmetic, not a trial result.
Alternatives
The swap lists mirror each other. For the leg press the app ranks the hack squat first (quads, compound, machine — full marks), then the barbell and dumbbell compounds (back squat, Bulgarian split squat, front squat, walking lunge), and the leg extension last as the isolation option. For the hack squat the leg press takes the top spot and the rest of the list is identical.
The short version
Same primary, same category, same rest, same step. Leg press: seated, sled pushed away, glutes and hamstrings credited. Hack squat: standing, sled squatted, glutes only. Leg extension: quads only, 60 s rest, higher reps. Pick by the machine you have and the range you want. Educational overview only — training guidance, not medical advice.