Semitendinosus Exercises: Strengthen Your Inner Hamstring

The semitendinosus is one of the three hamstring muscles, located on the inner back portion of your thigh. Its long tendon gives it its name ("semi" meaning half, "tendinosus" referring to its tendinous nature). This muscle is especially important for knee stability and is often used in ACL reconstruction surgery, making rehabilitation and strengthening particularly relevant for many people.

Understanding the Semitendinosus

Location: Back and inner side of the thigh

Origin: Ischial tuberosity (sit bone)—shares origin with biceps femoris long head

Insertion: Upper medial tibia at the pes anserinus—along with gracilis and sartorius

Key Feature: Has one of the longest tendons of any muscle, making it valuable for surgical grafting

Functions of the Semitendinosus

• Knee flexion: Bends the knee
• Hip extension: Extends the hip (pushes leg backward)
• Internal rotation of the tibia: Rotates the lower leg inward when knee is bent
• Knee stability: Supports the medial (inner) knee

The Semitendinosus and ACL Surgery

The semitendinosus tendon is commonly harvested for ACL reconstruction (along with gracilis). If you've had this surgery:

What Happens:

• The tendon is removed but the muscle belly remains
• The muscle can still function but may be weaker
• Over time, the tendon can partially regenerate

Implications:

• Initial weakness in knee flexion and internal rotation
• Importance of targeted rehabilitation
• May have 10-20% strength deficit long-term
• Strengthening becomes even more important

Exercises for the Semitendinosus

General Hamstring Exercises

Lying Leg Curl

1. Lie face down in leg curl machine
2. Curl weight toward buttocks
3. Lower with control
4. Perform 3 sets of 12 repetitions

Seated Leg Curl

1. Sit in seated curl machine
2. Curl heels under the seat
3. Control the return
4. Perform 3 sets of 12 repetitions

Romanian Deadlift

1. Hold weight with slight knee bend
2. Hinge at hips, lowering weight along legs
3. Feel hamstring stretch
4. Drive hips forward to stand
5. Perform 3 sets of 10 repetitions

Semitendinosus-Focused Exercises

Lying Leg Curl with Feet Turned In

1. Lie face down in leg curl machine
2. Turn feet/toes inward (internal rotation)
3. Curl weight toward buttocks
4. Lower with control
5. Perform 3 sets of 12 repetitions Internal rotation emphasizes medial hamstrings

Swiss Ball Leg Curl (Feet In)

1. Lie on back with heels on Swiss ball
2. Turn feet inward about 30 degrees
3. Lift hips and curl ball toward buttocks
4. Extend and repeat
5. Perform 3 sets of 12 repetitions

Single-Leg Bridge with Internal Rotation

1. Lie on back, one foot flat on floor
2. Turn foot inward
3. Lift hips into bridge position
4. Hold 3 seconds, lower
5. Perform 3 sets of 12 repetitions each leg

Slider Curl with Internal Rotation

1. Lie on back with heels on sliders
2. Turn feet inward
3. Lift hips into bridge, curl sliders toward buttocks
4. Extend and repeat
5. Perform 3 sets of 10-12 repetitions

Pes Anserinus Strengthening

Since the semitendinosus inserts at the pes anserinus with gracilis and sartorius, exercises that work all three can be beneficial:

Internal Rotation Against Resistance

1. Sit with knee bent 90 degrees
2. Attach band to outer ankle
3. Rotate lower leg inward against resistance
4. Control the return
5. Perform 3 sets of 15 repetitions each leg

Combined Knee Flexion and Internal Rotation

1. Lie prone, band around ankle
2. Curl knee while rotating foot inward
3. This mimics the muscle's combined actions
4. Perform 3 sets of 12 repetitions each leg

Eccentric Training

Eccentric Nordic Curl

1. Kneel with ankles secured
2. Slowly lower body forward (5 seconds)
3. Catch with hands, push back to start
4. Perform 3 sets of 5-6 repetitions

Eccentric Single-Leg Deadlift

1. Stand on one leg
2. Slowly hinge forward (4-5 seconds)
3. Return at normal speed
4. Perform 3 sets of 8 repetitions each leg

Stretching the Semitendinosus

To target the medial hamstrings specifically:

Seated Stretch with External Rotation

1. Sit with one leg extended
2. Turn toes outward (external rotation)
3. Lean forward from hips
4. Feel stretch on inner hamstring
5. Hold 30-45 seconds each side

Standing Stretch with Rotation

1. Place heel on elevated surface
2. Turn toes outward
3. Lean forward, keeping back straight
4. Hold 30-45 seconds each side

Supine Stretch with Strap

1. Lie on back, strap around foot
2. Lift leg toward ceiling
3. Rotate leg outward slightly
4. Feel stretch on medial hamstring
5. Hold 30-45 seconds each side

Rehabilitation After ACL Surgery (Hamstring Graft)

If your semitendinosus was used for ACL reconstruction:

Early Phase (Weeks 1-6):

• Focus on quad activation and knee extension
• Gentle hamstring isometrics (no resistance)
• Protect the healing graft
• Follow surgeon's protocol strictly

Intermediate Phase (Weeks 6-12):

• Begin light hamstring strengthening
• Closed chain exercises (bridges, squats)
• Progress gradually
• Monitor for pain at harvest site

Late Phase (Months 3-6):

• Progressive hamstring strengthening
• Address any remaining deficits
• Single-leg exercises
• Sport-specific preparation

Return to Sport (6-12 months):

• Comprehensive strength testing
• Hamstring strength should be 80-90%+ of other leg
• Functional testing passed
• Psychological readiness

Always follow your surgeon and physical therapist's guidance

Pes Anserinus Issues

Because the semitendinosus inserts at the pes anserinus, it can be involved in:

Pes Anserinus Bursitis/Tendinitis

• Pain at inner knee below joint line
• Worse with stairs and knee bending
• Tender to touch over pes anserinus
• Common in runners and overweight individuals

Treatment Approach:

• Relative rest from aggravating activities
• Ice and anti-inflammatory measures
• Address contributing factors (tight hamstrings, weakness)
• Strengthen all three pes anserinus muscles
• Gradual return to activity

Programming Considerations

For General Strength:

• Include hamstring work 2-3 times per week
• Mix bilateral and single-leg exercises
• Use various angles and rotations

For Injury Prevention:

• Emphasize eccentric training
• Nordic curls are highly effective
• Address strength ratios (hamstring:quad)
• Don't neglect flexibility

After ACL Surgery:

• Follow rehab protocol carefully
• Extra attention to hamstring strengthening
• Monitor for deficits compared to other leg
• Long-term maintenance important

When to Seek Help

Consult a healthcare provider if you experience:

• Sudden pain during activity with pop or tearing sensation
• Pain at inner knee that doesn't improve
• Significant weakness in knee flexion
• Swelling at back of thigh or inner knee
• Concerns about ACL graft or recovery

Summary

The semitendinosus is an important medial hamstring that contributes to knee flexion, hip extension, and internal rotation of the lower leg. Its role in knee stability and common use in ACL reconstruction make it particularly relevant for athletes and surgical patients alike. Target it specifically using internal rotation during leg curls and other hamstring exercises. If you've had ACL surgery with a hamstring graft, dedicated semitendinosus rehabilitation is essential for optimal recovery. Include both strengthening and flexibility work to maintain healthy, functional hamstrings.