How many sets and reps of the bent-knee windshield wiper should you do when you are new to the exercise?

Do 2 to 3 sets of 10 to 12 reps per side, since the bent knees keep the lever short enough for higher reps to still feel controlled. Rest about 45 seconds between sets. Move on to the lying windshield wiper with straighter legs only once you can keep the low back flat and the knees together through every rep here.

How do you make the bent-knee windshield wiper easier or harder?

Make it easier by rotating through a smaller range close to center, or by placing a small pillow under the knees for comfort while you build control. Make it harder by pausing for a second or two at each side before reversing, or by progressing to the lying windshield wiper with the legs straightened once this version feels easy.

Who is the bent-knee windshield wiper for, and when should you move past it?

It's an accessible entry point into loaded trunk rotation for anyone new to core rotation work or building back up after time off. It's a poor choice as a long-term oblique builder on its own, since the short lever limits how much resistance the obliques ever face once the pattern becomes easy.

Intermediate

Bent-Knee Windshield Wiper

Bending the knees shortens the lever compared with straight-leg wipers, making it an accessible entry into loaded trunk rotation. As the legs sweep from side to side, the obliques both create and control the rotation while the back stays anchored. It is a strong regression on the way to full hanging and straight-leg windshield wipers.

Equipment: Body Weight
Body part: Abs
Type: Functional, Strength
Browse by muscle: Abdominal External Oblique
Browse by movement: Rotation

How to do it

1
Lie on your back with arms out wide for a stable base.
2
Lift your knees so your hips and knees are bent to about ninety degrees.
3
Brace your abs and press your shoulders into the floor.
4
Rotate both knees down toward one side, stopping before your legs touch the floor.
5
Use your obliques to reverse and carry the knees across to the other side.
6
Keep alternating for reps, moving under control the whole time.

Tips

Keep both shoulder blades pinned to the mat so the rotation stays in the trunk.
Control the lowering; do not let gravity slam the legs to the side.
Reduce the range if your low back arches off the floor.

Variations

Common mistakes

The knees splay apart during the rotation instead of staying together, turning a clean two-legged wiper into two legs moving independently and diluting the oblique tension.
The tempo speeds up toward the end of the set, letting the legs' own weight carry them the last few inches to each side instead of the obliques controlling the arc.
The hips lift slightly off the floor as the knees rotate down, adding a small hip-thrust element that takes tension away from the trunk rotation this variation is meant to isolate.
Treating this as a warm-up to rush through before moving to straight-leg wipers skips the chance to actually build the trunk control the harder versions require.

Frequently asked

How many sets and reps of the bent-knee windshield wiper should you do when you are new to the exercise?: Do 2 to 3 sets of 10 to 12 reps per side, since the bent knees keep the lever short enough for higher reps to still feel controlled. Rest about 45 seconds between sets. Move on to the lying windshield wiper with straighter legs only once you can keep the low back flat and the knees together through every rep here.
How do you make the bent-knee windshield wiper easier or harder?: Make it easier by rotating through a smaller range close to center, or by placing a small pillow under the knees for comfort while you build control. Make it harder by pausing for a second or two at each side before reversing, or by progressing to the lying windshield wiper with the legs straightened once this version feels easy.
Who is the bent-knee windshield wiper for, and when should you move past it?: It's an accessible entry point into loaded trunk rotation for anyone new to core rotation work or building back up after time off. It's a poor choice as a long-term oblique builder on its own, since the short lever limits how much resistance the obliques ever face once the pattern becomes easy.

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