Exercise Overview
Straight leg raises are one of the most important early exercises after ACL surgery. They strengthen the quadriceps, hip flexors, and hip stabilizers without stressing the knee joint. SLRs are performed in four directions to target all the muscles around the hip.
Why SLRs Are Essential
- Strengthen quads without bending the knee
- Build hip strength needed for walking and stairs
- Prevent muscle atrophy during early recovery
- Safe to start in the first week post-op
- Foundation for all future strengthening
Eliminating Quad Lag
A key early milestone is performing SLRs without quad lag—meaning your knee stays completely straight throughout the lift. If your knee bends during the lift, focus on quad sets until you can maintain full extension. Using a knee brace locked at 0° can help initially.
The Four Directions
Perform SLRs in all four directions to strengthen the entire hip complex:
1. Flexion (Forward)
Position
Lying on your back
Target Muscles
Quadriceps, hip flexors (iliopsoas, rectus femoris)
Instructions
- Lie on your back, uninvolved leg bent
- Lock your surgical knee straight (quad set)
- Lift your leg 12-18 inches
- Hold 2-3 seconds, slowly lower
2. Abduction (Side)
Position
Lying on your uninvolved side
Target Muscles
Gluteus medius, gluteus minimus, TFL
Instructions
- Lie on your good side, body straight
- Keep surgical leg straight and slightly back
- Lift leg toward ceiling 12-18 inches
- Hold 2-3 seconds, slowly lower
3. Extension (Backward)
Position
Lying on your stomach (prone)
Target Muscles
Gluteus maximus, hamstrings
Instructions
- Lie face down on a firm surface
- Keep surgical knee straight
- Lift your leg 6-12 inches off surface
- Hold 2-3 seconds, slowly lower
Note: Range is smaller than other directions
4. Adduction (Cross)
Position
Lying on your surgical side
Target Muscles
Adductors (inner thigh muscles)
Instructions
- Lie on your surgical side
- Cross your uninvolved leg over
- Lift your bottom (surgical) leg up
- Hold 2-3 seconds, slowly lower
Detailed Instructions: Forward SLR
Starting Position
Lie on your back on a firm, flat surface. Bend your uninvolved leg with foot flat on the floor. Keep your surgical leg straight with toes pointing up.
Engage Your Quad
Perform a quad set first—tighten your thigh muscle and press your knee down. This locks your knee straight and is critical for proper form.
Lift Your Leg
While maintaining the quad contraction, lift your entire leg 12-18 inches off the surface (match the height of your bent knee). Keep the knee locked straight—no bending!
Hold at the Top
Hold for 2-3 seconds at the top. You should feel your quad and hip flexor working. Breathe normally—don't hold your breath.
Lower Slowly
Lower your leg slowly back to the starting position (3-4 seconds down). Rest briefly and repeat.
Common Mistakes
Quad Lag (Knee Bending)
If your knee bends during the lift, you're not ready for full SLRs. Use a brace locked at 0° or continue with quad sets until you can maintain extension.
Lifting Too High
Going higher than 18 inches doesn't provide more benefit and may cause hip flexor cramping. Match the height of your opposite bent knee.
Rotating the Leg
Keep your toes pointing straight up (or slightly out). Excessive rotation changes which muscles are working.
Holding Your Breath
Breathe normally throughout the exercise. Holding your breath increases blood pressure unnecessarily.
Dropping the Leg
Control the lowering phase—don't let your leg drop. The eccentric (lowering) portion is just as important for building strength.
Arching Your Back
Keep your lower back in a neutral position. If you're arching excessively, you may be lifting too high or have weak core muscles.
Sets, Reps & Frequency
| Phase | Sets | Reps | Hold | Frequency |
|---|---|---|---|---|
| Week 1-2 | 2-3 | 10 | 2-3 sec | 3x daily |
| Week 2-4 | 3 | 15 | 3 sec | 2-3x daily |
| Week 4-6 | 3 | 15-20 | 3 sec | 2x daily |
| Week 6+ | 3 | 15-20 | 3 sec | Daily or as warm-up |
Perform all four directions. If one direction is significantly weaker, add an extra set for that direction.
Progressions
Level 1: With Brace
Wear your brace locked at 0° if you have quad lag. This ensures proper form while you build strength.
Level 2: Without Brace
Once you can maintain full knee extension, perform without the brace.
Level 3: Add Ankle Weight
Start with 1-2 lbs, progress to 5+ lbs over time. Add weight when you can easily do 3x20.
Level 4: Slower Tempo
Increase time under tension: 3 seconds up, 5 seconds down.
Level 5: Standing Variations
Progress to standing hip flexion, abduction, and extension with resistance bands.
Pro Tips
Pair with Quad Sets
Always start your SLR session with a few quad sets to "wake up" the muscle and practice the contraction you'll need.
Quality Over Quantity
Ten perfect reps are better than twenty sloppy ones. If your form breaks down, rest and restart.
Track Your Progress
Note when you can do SLRs without the brace, when you add weight, and how many reps you can do without fatigue.
Don't Skip Adduction
The adduction (cross) SLR is often neglected but important for medial knee stability and overall hip balance.