Straight Leg Raise
What Is the Straight Leg Raise?
Straight Leg Raise is an isolation exercise that primarily targets the quads and also engages the hip flexors and the abdominal muscles that steady the pelvis. It is a beginner-level movement performed lying on your back with one knee bent and that foot flat, while the other leg, locked straight at the knee, is lifted off the floor and lowered under control.
It is one of the first strengthening exercises used in knee rehabilitation, after surgery such as an ACL reconstruction or a knee replacement and for knee pain and osteoarthritis, because it trains the thigh to hold the knee fully straight without bending the joint or loading it with body weight. Lifting the leg with no bend at the knee, often described as having no extensor lag, is a common milestone in post-operative knee programs before standing exercises are progressed.
The lift itself is hip flexion, so the work is shared between the deep hip flexors, the rectus femoris and the tensor fasciae latae, while the rest of the quadriceps hold the knee locked. Because the rectus femoris is the only quadriceps muscle that crosses the hip, the lift suits it well: a study of 28 sedentary women in their 40s found that a straight leg raise held at 60 degrees of hip flexion produced more rectus femoris activity than a partial wall squat or a seated knee extension, while a wall squat with a ball squeezed between the knees produced the most vastus medialis activity. Pairing it with the Quad Set and the Short Arc Quad, which load the vastus muscles more directly, covers the whole quadriceps.
This is a different exercise from the Lying Leg Raise, which lifts both legs together to train the abdominals, and from the Hanging Straight Leg Raise, a core exercise performed from a bar. Keeping the opposite knee bent anchors the pelvis, so the load stays modest enough for early rehab.
The straight leg raise suits older adults, people with limited mobility and clients returning from a knee injury, since it needs no equipment and can be done on a firm bed. Anyone who cannot keep the knee straight through the lift should build up with quad sets first. Once several sets feel easy with the knee fully locked, a light ankle weight adds resistance before moving on to standing work such as the Bodyweight Squat.
Muscles Worked
- Rectus Femoris
- Primary
- Adductor Longus
- Medium
- Sartorius
- Medium
- Vastus Lateralis
- Medium
- Vastus Medialis
- Medium
- Tibialis Anterior
- Minimal
Instructions
- Lie on your back on a mat, a firm bed or the floor with your arms resting at your sides, palms down.
- Bend one knee and set that foot flat on the floor.
- Straighten the other leg along the floor and pull the toes toward you.
- Tighten the front of the straight thigh so the back of the knee presses down and the knee locks straight.
- Brace your abdominals gently so your lower back stays resting on the floor.
- Keeping the knee locked, lift the straight leg until it is roughly in line with the bent thigh.
- Pause for 1 to 2 seconds at the top without letting the knee bend or the leg roll outward.
- Lower the leg slowly until the heel rests on the floor, then relax the thigh and tighten it again before the next rep.
- Complete your reps, then switch sides.
Common Mistakes
Bending the lifting knee
Letting the knee soften as the leg rises hands the work to the hip flexors and hides the quadriceps weakness the exercise is meant to fix.
Skipping the quad set
Lifting before the thigh is tightened and the knee pressed straight makes the knee bend partway through the rep.
Arching the lower back
Letting the pelvis tip forward as the leg lifts strains the lower back instead of keeping the work on the thigh and hip.
Dropping the leg
Letting the leg fall back to the floor skips the slow lowering, which is half of the strengthening work.
Letting the leg roll outward
Turning the knee and toes out shifts the lift toward the inner thigh and lets the pelvis twist.
Injuries
Straight Leg Raise is a low risk exercise when performed with proper technique. The leg is light, the range is short and the knee joint itself stays still, which is why the movement is used so early after knee surgery.
The lower back is the most common complaint. If the abdominals do not hold the pelvis, the lifting leg pulls it forward into an arch, so keep the opposite knee bent and the lower back resting gently against the floor. The front of the hip can also become irritated, because the hip flexor tendons do much of the lifting. Pain in the groin or the front of the hip during the lift, particularly after a hip replacement, is worth reporting to the surgeon or physical therapist rather than pushing through. After any knee or hip surgery, follow the timing and range they set.
If the knee bends as the leg lifts, the quadriceps are not yet strong enough to hold it straight. Go back to the Quad Set, lift only a few inches, or have a helper support the ankle on the way up, and use the Heel Slide to work on knee motion. To progress, hold the top position longer, add a light ankle weight, or move on to the Machine Leg Extension and standing exercises.
Stop if you feel sharp or increasing pain in the knee, hip or lower back, if the knee swells after the session, or if you cannot keep the knee straight even with a smaller lift.
- Primary Focus
- Quads
- Equipment
- Body weight
- Modality
- Strength
- Difficulty
- Beginner
Alternative Exercises
Frequently Asked Questions
- Q: Does the straight leg raise really strengthen the quads?
Partly. The quadriceps contract to hold the knee locked and the rectus femoris helps lift the leg, but much of the lift comes from the deep hip flexors: in seven healthy men scanned right after the exercise, the psoas and iliacus showed more glucose uptake than the vastus medialis and vastus lateralis. That is why it is usually paired with exercises that load the vastus muscles more directly, such as the Quad Set.
- Q: Why does the other knee stay bent?
With the opposite foot flat on the floor, the pelvis stays anchored and the lower back is less likely to arch as the leg lifts. It also keeps the load low enough that the exercise stays a thigh and hip exercise rather than an abdominal one.
- Q: How is this different from a lying leg raise?
The Lying Leg Raise lifts both straight legs together and is an abdominal exercise, while the straight leg raise lifts one leg with the other knee bent to train the thigh and hip flexors. The Hanging Straight Leg Raise is a harder core exercise done hanging from a bar.
- Q: What should I do if my knee bends when I lift?
A knee that bends as the leg rises means the quadriceps cannot yet hold it straight. Relax the leg, tighten the thigh again until the knee is fully locked before each rep, and if it still bends, spend more time on quad sets or lift only a few inches until it stays straight.
- Q: Can I do straight leg raises in bed?
Yes. A firm mattress works as long as the bent foot has a stable surface to press into and the hips do not sink, which makes it a practical option for anyone who struggles to get down to the floor.
- Q: When should I add an ankle weight?
Once you can do 3 sets of 12 to 15 lifts with the knee fully straight and no pain, add a light ankle weight of about 1 pound (0.5 kg) and increase it gradually. After surgery, wait until your surgeon or physical therapist clears added resistance.