A seated knee extension straightens the knee while your thigh stays on a chair. It is sometimes called a long arc quad exercise. The quadriceps at the front of your thigh do the lifting. Unlike a straight leg raise, the knee moves through a bend instead of staying straight while the whole leg rises.
Start with the version you were prescribed
A chair exercise can look simple while still needing a specific range or load. The NHS OPAL guide demonstrates straightening the knee from sitting and lowering with control. Its progression options include resistance, but that does not mean an ankle weight belongs in every recovery plan. Check whether your instruction is for movement practice, a timed hold, or strengthening against resistance.
Make the setup repeatable
- Use a stable chair and support your thigh. Start with your feet resting comfortably on the floor.
- Straighten the knee through the range your therapist demonstrated, without swinging the leg to reach the end.
- Return slowly enough to control the movement. Keep the chair position the same when comparing sessions.
- Check the written instruction for which leg, repetitions, holds and rest. Do not fill in missing details from a different exercise video.
If the seat edge presses behind your knee or you have to lean far backwards to lift the foot, ask your therapist to check the chair height and position. A useful demonstration includes both the starting position and the return, not just a photograph of the leg held straight.
After surgery, the operation changes the rules
ACL reconstruction and knee replacement are different procedures. Cambridge University Hospitals gives different open-chain knee-extension guidance according to ACL graft type, including restrictions on resistance and movement range. Those details are a reason to follow your own surgical team, not a reason to copy a timetable from another patient. A brace setting or an additional procedure may also change your instructions.
What to bring to the next review
Record whether you completed the planned movement, what resistance you actually used, and where any discomfort occurred. For example, “I could straighten without the weight, but stopped when I added it” gives your therapist a concrete question to investigate. Avoid substituting extra repetitions for a range you cannot comfortably reach.
For the exercise where the knee stays straight while the leg lifts, read about straight leg raises
Stop if the exercise causes sharp pain, new swelling or a feeling that the knee is giving way. After surgery, confirm your permitted range and resistance with your treating team before changing either.