Semitendinosus

A Medial Hamstring for Sprinting, Deceleration, and Dynamic Knee Stability

The semitendinosus (ST) is one of the major hamstring muscles and contributes to knee flexion, hip extension, and internal rotation of the tibia.

For athletes, its importance extends well beyond simply bending the knee. The hamstrings play major roles during sprinting, jumping, acceleration, and rapid deceleration, while the semitendinosus often demonstrates substantial recruitment during knee-dominant and eccentric hamstring tasks.¹˒²

The semitendinosus is also clinically relevant because the medial hamstrings contribute to dynamic knee stability, including neuromuscular control during cutting and landing tasks.

Anatomy of the Semitendinosus

Origin

The semitendinosus originates primarily from the:

ischial tuberosity.

Proximally, it shares a conjoint tendinous and aponeurotic relationship with the long head of the biceps femoris.

An anatomical study also found additional semitendinosus muscle fibers arising consistently from the medial aspect of the proximal biceps femoris long head.⁵

This anatomy suggests a mechanical relationship between the two muscles rather than two completely independent structures.

Insertion

Distally, the semitendinosus transitions into a long tendon that inserts onto the:

superior anteromedial surface of the proximal tibia.

Together with the sartorius and gracilis tendons, it forms the:

**pes anserinus.**⁶

Primary Actions

The primary actions of the semitendinosus include:

• Knee flexion
• Hip extension
• Internal rotation of the tibia when the knee is flexed⁶

Exercise 1 | Nordic Hamstring Exercise

The Nordic Hamstring Exercise (NHE) is one of the best-supported exercises for targeting the semitendinosus.

The athlete lowers the trunk forward from a kneeling position while using the hamstrings to eccentrically resist knee extension.

Functional MRI and high-density EMG studies have reported particularly high semitendinosus recruitment during the Nordic, including greater activity than the biceps femoris long head under some testing conditions.⁷˒⁸

Why Is It Useful?

The Nordic provides more than acute muscle activation.

Training studies have reported structural adaptation of the semitendinosus, including increases in:

• Fascicle length
• Muscle thickness
• Muscle volume⁹⁻¹¹

This makes it particularly valuable when developing high-force eccentric capacity.

However, the Nordic is demanding. Early rehabilitation or less-trained athletes may require shorter ranges of motion, assistance, or lower-volume exposure before progressing to full repetitions.

Exercise 2 | Romanian Deadlift

The Romanian Deadlift (RDL) provides a different stimulus by loading the hamstrings primarily through hip flexion and extension.

Studies in female athletes have demonstrated greater semitendinosus than biceps femoris activation during RDL variations.¹²˒¹³

Why Is It Useful?

The Nordic is predominantly a knee-dominant eccentric task, whereas the RDL is much more hip dominant.

Combining the two allows the athlete to train both major functions of the semitendinosus:

knee flexion + hip extension.

The RDL also loads the hamstrings at relatively long muscle lengths, making it useful within strength and return-to-sport programming.

Exercise 3 | Kettlebell Swing

The Kettlebell Swing can also produce substantial semitendinosus activation.

EMG research has found both kettlebell swings and Romanian deadlifts to favor the semitendinosus over the biceps femoris in several athlete populations.¹²˒¹³

The key difference from the RDL is speed.

The kettlebell swing adds a more ballistic hip-extension demand, making it useful later in a progression when the athlete needs to transition from controlled strength toward rapid force production.

< Take-Home Message >

The semitendinosus is much more than a knee flexor.

For athletes, it contributes to:

sprinting, deceleration, hip extension, and dynamic control of the knee.

Reduced semitendinosus pre-activation during cutting has been associated with subsequent ACL injury in female athletes,³ and athletes who have undergone ACL reconstruction using a semitendinosus tendon graft may demonstrate persistent changes in semitendinosus recruitment and hamstring coordination.²˒⁴

Evidence-supported exercise options include the:

Nordic Hamstring Exercise, Romanian Deadlift, and Kettlebell Swing.

Rather than searching for a single “best” semitendinosus exercise, training should progressively prepare the muscle to work with the rest of the hamstrings, gluteal muscles, and lower extremity during high-speed athletic movement.

The ultimate goal is not simply a strong semitendinosus.

It is a semitendinosus that can produce and absorb force at the right magnitude, length, and timing for the demands of sport.