TETSUBottoms-Up vs Machine Kneeling Twist
The Bottoms-Up and the Machine Kneeling Twist both train the abs as their primary muscle. The Bottoms-Up is bodyweight-only while the Machine Kneeling Twist uses a machine. Here is how they compare and when to pick each.
Side-by-side comparison
| Bottoms-Up | Machine Kneeling Twist | |
|---|---|---|
| Primary muscle | abs | abs |
| Body part | waist | waist |
| Supporting muscles | obliques and hip flexors | obliques and lower back |
| Equipment | bodyweight | machine |
| Steps in our guide | 5 | 6 |
How each one starts
Bottoms-Up — first steps
- Lie flat on your back with your legs extended and your arms by your sides.
- Bend your knees and bring them towards your chest, keeping your feet off the ground.
Machine Kneeling Twist — first steps
- Adjust the seat height and position yourself on the machine with your knees resting on the pads and your upper body facing forward.
- Grasp the handles or the sides of the machine for stability.
Full step-by-step guides are linked below.
Which should you choose?
The Bottoms-Up needs no equipment and scales through leverage, tempo and reps. The Machine Kneeling Twist 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 Bottoms-Up better than the Machine Kneeling Twist?
Neither is universally better — both train the abs as the primary mover. The Bottoms-Up needs no equipment and scales through leverage, tempo and reps, while the Machine Kneeling Twist 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 Bottoms-Up and the Machine Kneeling Twist 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 Bottoms-Up and the Machine Kneeling Twist work the same muscles?
The primary muscle is the same: the abs. Supporting muscles differ slightly — obliques and hip flexors for the Bottoms-Up versus obliques and lower back for the Machine Kneeling Twist.
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.