TETSU3/4 Sit-Up vs Machine Seated Crunch (Chest Pad)
The 3/4 Sit-Up and the Machine Seated Crunch (Chest Pad) both train the abs as their primary muscle. The 3/4 Sit-Up is bodyweight-only while the Machine Seated Crunch (Chest Pad) uses a machine. Here is how they compare and when to pick each.
Side-by-side comparison
| 3/4 Sit-Up | Machine Seated Crunch (Chest Pad) | |
|---|---|---|
| Primary muscle | abs | abs |
| Body part | waist | waist |
| Supporting muscles | hip flexors and lower back | obliques |
| Equipment | bodyweight | machine |
| Steps in our guide | 5 | 7 |
How each one starts
3/4 Sit-Up — first steps
- Lie flat on your back with your knees bent and feet flat on the ground.
- Place your hands behind your head with your elbows pointing outwards.
Machine Seated Crunch (Chest Pad) — first steps
- Adjust the seat height and chest pad position according to your comfort.
- Sit on the machine with your back against the chest pad and your feet flat on the floor.
Full step-by-step guides are linked below.
Which should you choose?
The 3/4 Sit-Up needs no equipment and scales through leverage, tempo and reps. The Machine Seated Crunch (Chest Pad) fixes the movement path so you can push close to failure with less skill demand. If your gym has both options, neither is a wrong choice: pick the one that feels strongest through a full range, and swap after 6 to 8 weeks to keep the abs adapting.
Full form guides
Common questions
Is the 3/4 Sit-Up better than the Machine Seated Crunch (Chest Pad)?
Neither is universally better — both train the abs as the primary mover. The 3/4 Sit-Up needs no equipment and scales through leverage, tempo and reps, while the Machine Seated Crunch (Chest Pad) fixes the movement path so you can push close to failure with less skill demand. Choose based on your equipment and which movement you can progress consistently.
Can I do both the 3/4 Sit-Up and the Machine Seated Crunch (Chest Pad) in the same program?
Yes, but usually not in the same session — they overlap heavily on the abs. A common setup is one as your main movement and the other on a second training day, or alternating them block by block.
Do the 3/4 Sit-Up and the Machine Seated Crunch (Chest Pad) work the same muscles?
The primary muscle is the same: the abs. Supporting muscles differ slightly — hip flexors and lower back for the 3/4 Sit-Up versus obliques for the Machine Seated Crunch (Chest Pad).
Track it in Tetsu
Tetsu tracks both movements separately, keeps your PRs per exercise, and tells you which one is actually progressing. Free to start.