The Hamstrings are actually comprised of three separate muscles: the Biceps Femoris, Semitendinosus and Semimembranosus.
Anatomy Chart courtesy of FCIT
These muscles originate just underneath the Gluteus Maximus on the pelvic bone and attach on the tibia.
The Hamstrings are primarily fast-twitch muscles, responding to low reps and powerful movements.
Functions of the Hamstring Muscles
The "commonly thought of" primary functions of the Hamstrings are knee flexion (bringing the heel towards the buttocks) and hip extension (moving the leg to the rear).
An example of knee flexion is the leg curl exercise and an example of hip extension is the stiff-legged deadlift exercise.
In movement, the hamstrings "primary" function is NOT knee flexion. In walking or running, for example, the primary function of the hamstring is to decelerate the lower leg in the sagittal plane. Positionally, knee flexion in walking/running occurs as a result of hip flexion and plantar flexion, again positionally. When the body responds to gravity, function changes (thank you to Jonathan Hewitt, APT - Athletic Enhancement Systems, for this contribution!)
Exercises that work the Hamstrings include:
Visit the Hamstring and Adductor Exercise Index for more movements to work your hamstrings.
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