Exercise Overview
Prone hangs are one of the most important exercises in early ACL recovery. They use gravity to help restore full knee extension (straightening)—a critical milestone that directly affects your ability to walk normally, climb stairs, and run.
Why Extension Matters So Much
Full knee extension is the #1 priority in early ACL recovery. Losing even a few degrees can lead to:
- Altered walking pattern (limp)
- Increased patellofemoral (kneecap) problems
- Quad weakness and inhibition
- Long-term knee pain and dysfunction
- Difficulty returning to sport
Goal: Match your uninvolved knee's extension (typically 0° or slight hyperextension)
How To Perform
Set Up
Lie face down (prone) on a bed, table, or firm couch with your kneecaps at the edge. Both legs should hang off the edge from just above the kneecap.
Relax Completely
Let your legs completely relax and hang. Gravity will gently pull your knees toward straight. Don't actively push—just relax and let gravity work.
Hold Position
Hold this position for 10-15 minutes. You may feel a gentle stretch in the back of your knee. This should not be painful—just a mild stretching sensation.
Add Weight If Needed
If you're not making progress, you can place a light weight (1-5 lbs) on your ankle to provide additional stretch. Only add weight if your PT approves.
Compare to Other Leg
Periodically compare your surgical leg's extension to your other leg. Your goal is to match it exactly.
Alternative Extension Exercises
Supine Hang
Lie on your back with a towel roll under your ankle (not under your knee). Let your knee straighten toward the bed. Can add weight on thigh.
Heel Prop
Sit or lie down with your heel propped on a rolled towel or foam roller. Let your knee drop toward the surface.
Standing Extension
Stand and actively push your knee back into full extension. Hold for 10-30 seconds. Good for active extension.
Low-Load Long-Duration Stretch
Use a very light weight or stretch strap for 15-30 minutes. Research supports this approach for extension gains.
Frequency & Duration
| Phase | Duration | Frequency | Weight |
|---|---|---|---|
| Week 0-2 | 10-15 min | 3-4x daily | None |
| Week 2-4 | 15-20 min | 3x daily | 1-2 lbs if needed |
| Week 4-6 | 15-20 min | 2-3x daily | 2-5 lbs if needed |
| Once achieved | 5-10 min | Daily (maintenance) | As needed |
Continue until you have full extension matching your other knee. Then maintain with daily sessions. Extension can be lost if not maintained!
Troubleshooting
I'm not making progress
Try adding a light ankle weight (1-2 lbs) or increasing frequency to 4-5 times daily. Longer duration at low load is more effective than short duration with more weight.
It's painful
A mild stretching sensation is normal; sharp pain is not. If painful, try without weight, reduce duration, or consult your PT. Some discomfort is expected but you shouldn't be grimacing.
My swelling limits extension
Swelling is a common barrier to extension. Ice after prone hangs, elevate frequently, and use compression. Managing swelling helps extension return.
How do I know when I have full extension?
Compare to your other leg. Lie flat and see if both knees touch the surface equally. If you naturally hyperextend (knee bends backward), your surgical leg should match.