Hamstrings
Biceps femoris, semitendinosus, semimembranosus
Pronunciation: HAM-strings
For beginners
The hamstrings run down the back of your thigh and do two jobs: they help drive your hip backward (like in a deadlift) and they bend your knee (like in a leg curl).
Show the advanced explanation
Because they cross both the hip and the knee, hamstrings can be lengthened at one joint while shortened at the other (e.g., hip flexed, knee extended, as in a Romanian deadlift) — this is why RDL-style hip-hinge exercises stretch and load the hamstrings so effectively.
Structure & function
- Location
- The muscle group covering the back of the thigh, made of three muscles.
- Origin
- Ischial tuberosity (the 'sit bone') of the hip bone; the short head of biceps femoris arises from the femur.
- Insertion
- Fibula (biceps femoris) and tibia (semitendinosus, semimembranosus), below the knee.
- Main action(s)
- Extends the hip and flexes the knee — a biarticular (two-joint) muscle group that works closely with the gluteus maximus in hip extension.
- Joint(s) crossed
- Hip joint and knee joint
- Movement plane
- sagittal
- Innervation
- Sciatic nerve (tibial and fibular divisions, L5–S2)
- In daily movement
- Slowing the leg down as you walk, and helping propel you forward during the push-off phase.
- In exercise
- Assists the gluteus maximus in hip-hinge exercises (deadlifts) and is the prime mover of knee flexion in leg curls.
- Commonly confused with
- Their hip-extension role is sometimes overlooked in favor of the gluteus maximus; in reality both work together in most hip-extension lifts.
- Common misconceptions
- Hamstring 'tightness' during a forward bend is not always about muscle length — it can also reflect nervous-system sensitivity or simply insufficient hip-hinge practice.
Exercises that use this muscle
As a primary mover
As a secondary / stabilizer
- Barbell Back Squat (secondary)
⚠ Safety note
A sudden sharp pain or 'pop' in the back of the thigh, especially during sprinting, is a classic hamstring strain sign and needs assessment before returning to training.
Sources
“The hamstring muscles extend the thigh at the hip and flex the leg at the knee.”
Anatomy and Physiology 2e — OpenStax, Rice University · Ch. 11.6 Appendicular Muscles of the Pelvic Girdle and Lower Limbs
Peer-reviewed textbook · License: CC BY-NC-SA 4.0 · Last checked 2026-07-19
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