What Muscles Do Lying Leg Curls Work?

Lying leg curls—also called prone leg curls—work your hamstrings through knee flexion while lying face down. This classic exercise isolates the hamstrings effectively and has been a gym staple for decades. While the hip-extended position may provide less stretch than seated curls, it still delivers excellent hamstring development.

Quick Answer

Primary muscles: Hamstrings (all three muscles)

Secondary muscles: Gastrocnemius (assists knee flexion), popliteus

What makes it unique: The prone position with hips extended creates a shortened hamstring position at the hip while working through knee flexion—different stimulus than seated curls.

Complete Muscle Breakdown

Hamstrings (Maximum Activation)

All three hamstring muscles work during lying leg curls:

Biceps Femoris (Long Head)

• Location: Lateral (outer) hamstring
• Crosses: Hip and knee joints
• In lying curls: Shortened at hip, working at knee
• Strong activation: Primary knee flexor

Biceps Femoris (Short Head)

• Location: Lateral hamstring, deeper
• Crosses: Only the knee
• In lying curls: Works identically regardless of hip position
• Consistent activation: In all leg curl variations

Semitendinosus

• Location: Medial (inner) hamstring
• Crosses: Hip and knee
• In lying curls: Works through full knee flexion
• Strong activation: Throughout the movement

Semimembranosus

• Location: Deep medial hamstring
• Crosses: Hip and knee
• In lying curls: Works with semitendinosus
• Strong activation: Primary mover

Gastrocnemius (Secondary)

The calf muscle assists with knee flexion:

• Anatomy: Crosses behind the knee
• Contribution: Minor assistance
• Not the target: But contributes to the movement
• Can cramp: If it takes over (indicates hamstring weakness)

Popliteus (Minor)

Small muscle behind the knee:

• Function: Assists knee flexion, unlocks the knee
• Contribution: Very minor
• Not significant: For overall movement

Lying vs. Seated Leg Curls

Hip Position Differences

| Aspect | Lying (Prone) | Seated | |--------|---------------|--------| | Hip position | Extended | Flexed | | Hamstring at hip | Shortened | Stretched | | Hamstring length | Shorter overall | Longer overall | | Peak contraction | May feel stronger | May feel more stretch |

Which Is Better?

Both have value:

• Lying curls: Strong contraction, classic feel
• Seated curls: More stretch, possibly more growth stimulus
• Best approach: Include both in your program
• Variety: Benefits overall development

Research Perspective

Some studies suggest:

• Stretched-position training (seated) may enhance growth
• But lying curls are still highly effective
• Don't overthink—train both variations
• Consistency matters more than which variation

Proper Lying Leg Curl Technique

Machine Setup

1. Lie face down on the machine
2. Align knees just off the edge of the pad (at pivot point)
3. Position ankle pad on lower calves/Achilles area
4. Hips flat against the pad
5. Grip handles for stability

The Movement

1. Start with legs nearly straight (slight bend)
2. Curl heels toward your glutes
3. Squeeze hamstrings throughout
4. Continue until full knee flexion
5. Hold briefly at peak contraction
6. Lower with control back to start
7. Maintain hip contact with the pad throughout

Key Cues

• "Curl your heels to your butt"
• "Keep your hips down"
• "Squeeze at the top"
• "Control the negative"
• "Don't let it drop"

Common Mistakes

Lifting Hips Off the Pad

Hips must stay down:

• Lifting hips reduces hamstring work
• Brings in hip flexors and low back
• If hips lift, weight is too heavy
• Reduce load and maintain position

Using Momentum

Control every rep:

• No swinging or jerking
• 2-3 seconds to curl
• 2-3 seconds to lower
• Feel the hamstrings working

Partial Range of Motion

Full range is essential:

• Full extension (nearly straight, not locked)
• Full flexion (heels close to butt)
• Don't cheat range for more weight
• Full ROM = full development

Pointing Toes (Plantarflexion)

Keep feet neutral or dorsiflexed:

• Pointing toes engages calves more
• Reduces hamstring isolation
• Neutral or toes-toward-shin is better
• Reduces calf cramping too

Hyperextending at Start

Don't lock out the knees:

• Start with a slight bend
• Protects the joint
• Maintains tension on hamstrings
• Safer and more effective

Programming Lying Leg Curls

For Hamstring Hypertrophy

• Sets/reps: 3-4 sets of 10-15 reps
• Tempo: Controlled throughout
• Frequency: 2x per week
• Focus: Mind-muscle connection

For Strength

• Sets/reps: 4 sets of 6-10 reps
• Load: Challenging but with full ROM
• Frequency: 1-2x per week
• Focus: Progressive overload

For Injury Prevention (Athletes)

• Sets/reps: 3 sets of 12-15 reps
• Tempo: Controlled with eccentric emphasis
• Frequency: 2-3x per week
• Focus: Building resilient hamstrings

Sample Hamstring Workout

Balanced Hamstring Day:

1. Romanian deadlift: 4x8 (hip dominant)
2. Lying leg curl: 4x12 (knee dominant)
3. Good morning: 3x10 (hip dominant)
4. Seated leg curl: 3x12 (knee dominant, stretched)

Lying Leg Curl Variations

Standard Lying Leg Curl

• Both legs working together
• Most common version
• Foundation for other variations

Single-Leg Lying Curl

• One leg at a time
• Addresses imbalances
• Higher intensity per leg
• Identifies weak side

Pause Rep Lying Curl

• 2-3 second pause at peak contraction
• Eliminates momentum
• Maximum squeeze
• Very challenging

Eccentric Emphasis Lying Curl

• Curl with both legs
• Lower with one leg (slow)
• Builds eccentric strength
• Great for injury prevention

ISO Hold Lying Curl

• Hold at peak contraction for time
• 10-30 second holds
• Isometric strength
• Different stimulus

Drop Set Lying Curl

• Perform to near failure
• Reduce weight immediately
• Continue without rest
• Repeat 2-3 times
• Intense finisher

Who Should Do Lying Leg Curls?

Ideal For

• Anyone wanting hamstring development
• Gym-goers (machine commonly available)
• Beginners (easy to learn)
• Bodybuilders (isolation work)

Great For

• Pairing with hip-dominant exercises
• Pre-exhausting hamstrings
• Finishing leg day
• Addressing knee-flexion strength

Safe For Most People

Lying leg curls are generally safe:

• Machine provides stability
• Controlled movement
• Easy to adjust load
• Appropriate for most populations

Use Caution If

• You have acute hamstring strain
• You have low back issues (lying position)
• The pad causes discomfort
• Movement causes pain

Complete Hamstring Training

Two Functions of Hamstrings

Hamstrings do two things:

1. Hip extension: RDL, good morning, hip thrust
2. Knee flexion: Leg curls

Training Both Functions

For complete development:

• Include hip-dominant exercises (deadlifts, RDL)
• Include knee-dominant exercises (leg curls)
• Both functions matter
• Neither alone is complete

Sample Weekly Split

Day 1 (Pull/Posterior):

• Deadlift: 4x5
• Lying leg curl: 4x10

Day 2 (Legs):

• Squat: 4x6
• Romanian deadlift: 3x8
• Seated leg curl: 3x12

The Bottom Line

Lying leg curls work all three hamstring muscles through knee flexion in a classic, proven exercise. While the prone position creates a shortened hamstring at the hip (compared to seated curls), it still delivers excellent development and has built countless pairs of strong hamstrings.

Include lying leg curls as part of a complete hamstring program that also addresses hip extension. The combination of hip-dominant and knee-dominant exercises creates the balanced development your hamstrings need for strength, size, and injury prevention.

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