This assessment takes 20–25 minutes at any gym with a knee extension machine. You'll test both legs to measure quad strength symmetry — that single number determines where you start in ACL Bridge.
What this tells us
Quad LSI
Limb Symmetry Index
Your involved leg's strength as a percentage of your uninvolved leg. The gold standard for measuring where you are in the return-to-performance window — not time since surgery, not how you feel, but how you actually load.
Why the 5RM
5-Rep Max on the Knee Extension
The heaviest weight you can lift for exactly 5 clean reps. Simple, reliable, and honest — you can't fake both legs on the same machine.
You'll need
A gym with a knee extension machine · 20–25 minutes · Something to record your weights
Step 1 of 3 — Prepare
Warm-up protocol.
Do not skip this. A cold muscle test gives you inaccurate numbers and affects your entire program placement.
Complete in order
1
5 minutes easy cardio
Stationary bike or brisk walk. Easy pace — circulation, not a workout.
2
Knee extension warm-up sets
2 sets × 15 reps at ~30% effort. Light and controlled, full range of motion.
3
Rest 2 minutes
Sit down, shake out your legs. Don't rush into testing.
Step 2 of 3 — Setup
Set up the machine.
Same setup both legs, every time you retest. Consistency here is everything.
Machine position checklist
✓
Seat back: Thigh fully supported, knee at edge of pad. Hip ~90°.
✓
Ankle pad: Lower shin, just above the ankle.
✓
Range of motion: Start at 90°, finish at full extension. No shortcuts.
✓
Same position, both legs. Don't adjust the seat between sides.
✓
Tempo: 2 sec up · 1 sec pause · 2 sec down. No momentum.
Test uninvolved side first
Always test your non-surgical leg first. It gives you an accurate baseline and a target to reach toward.
Step 3a — Uninvolved Side
Test your stronger leg first.
Work up to the heaviest weight you can complete for exactly 5 clean reps.
1
Attempt 1 — Moderate
~60% of estimated max. Complete 5 reps. Rest 3 minutes.
2
Attempt 2 — Heavier
Add 10–20 lbs. 5 reps if you can. Rest 3 minutes.
3
Attempt 3 — Your 5RM
Add 5–10 lbs. 5 clean reps = your number. If form breaks by rep 3, step back.
Uninvolved leg 5RM
lbs
The weight you completed for 5 clean reps.
Step 3b — Involved Side
Now test your surgical leg.
Same protocol, same tempo, same position. Rest at least 5 minutes from your last uninvolved set.
Important
Start conservatively. There's no right answer here — only an honest one. Do not push through sharp pain or instability.
1
Start at 50% of your uninvolved score
Your conservative baseline. Complete 5 reps and assess before adding weight.
2
Work up in 5–10 lb increments
Same 2-1-2 tempo throughout.
3
Record your 5RM
Same standard as the uninvolved side — full range, controlled, no compensation.
Involved leg 5RM
lbs
Be honest — this score only helps you if it's accurate.
Any pain during testing?
Mild = minor ache, resolves within an hour. Moderate = pain that altered movement or lingered.