Lower trunk rotation, often called knee rolls, is a gentle mobility exercise for the lower back. You lie on your back with your knees bent and slowly let both knees roll from side to side. Physios often give it for a stiff lower back. The aim is easy movement rather than a big stretch.

How to do the lower trunk rotation

Lie on your back on a mat, knees bent and feet flat on the floor. Keep your knees and feet close together.
Rest your arms by your sides, palms down. This keeps your upper body steady.
Slowly let both knees roll to one side. Your feet stay on the floor and will roll onto their edges, which is fine.
Go only as far as is comfortable. Both shoulders stay resting on the floor.
Hold the knees there for 3 to 5 seconds. You may feel a light stretch in your hips and lower back.
Tighten your stomach gently to bring the knees back to the middle, then roll them to the other side and hold again.

What you should feel

Easy movement in the lower back, and a light stretch through the back and the side of the hips at the end of each roll.

Common mistakes

Letting the knees flop to the side. Control them on the way over and on the way back.
Lifting the opposite shoulder off the floor to get more range.
Pushing into a range that hurts. Small and easy is enough.

How often

Often 10 to 15 slow rolls to each side, with a hold of 3 to 5 seconds at the end of each roll, once or twice a day. You can repeat them whenever the back feels stiff. Your physio will adjust the numbers.

Stop and check with your physio if

Pain spreads down the leg or you get numbness or tingling.
You feel sharp or catching pain in the back at any point. Make the movement smaller, and stop if it keeps happening.

From the clinic

Knee rolls are often used as a warm up before other back exercises, and some people find first thing in the morning the easiest time to fit them in. Rhythm matters more than range: slow and smooth, breathing out as the knees go over.

It is common for one side to feel tighter. Stay in the easy range on that side rather than forcing it, and it may loosen a little over a few rolls. As the movement gets easier, your physio may change how long you hold at each end.

With low bone density (osteoporosis), keep the rolls small and gentle. Twisting right to the end of the range is usually avoided.

If you have had a hip replacement, get the go-ahead from your surgeon or physio before you try this exercise. As the knees roll to one side, the upper knee turns that hip inward and across the middle of your body, and many surgeons ask you to avoid that for the first months after some operations. If you are pregnant, ask your physio whether to keep doing these flat on your back once you are past the first trimester.

Reviewed by the PocketPhysio by VirtueLife expert physiotherapy team. Last reviewed 2026-09-25.

This page is general education, not a diagnosis or a personal treatment plan. If you have pain, an injury or a health condition, see a physiotherapist or doctor before starting new exercises.

Lower trunk rotation