Hamstring Muscles: Functional Anatomy Guide

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The Anatomy of the Hamstring Muscles

At the back of the upper leg behind the thigh (quadriceps) there are three muscles known as the hamstrings. They are the antagonistic muscles to the quads.

The hamstrings in the back of the thigh consist of three separate muscles:

  1. The biceps femoris (long and short head)
  2. The semitendinosus
  3. The semimembranosus

Each of these muscles originates just underneath the gluteus maximus (the main butt muscle) on the pelvic bone and attaches to the tibia. Every hamstring muscle is a two-joint muscle, whereas only one quad muscle is a two-joint muscle.

The anatomy of the hamstring muscles

The anatomy of the hamstring muscles

Location of the Hamstring Muscles

As we have already mentioned, the hamstring muscles run along the back of your thigh, from your pelvis to your lower leg.

Other Names

  1. Thigh (Rear)
  2. Posterior thigh
Hamstring Muscles: Functional Anatomy Guide

Hamstring Muscles: Functional Anatomy Guide

Biceps Femoris

The largest muscle of the hamstrings is the biceps femoris. Like the biceps in your upper arm the largest of the hamstring muscles (biceps femoris) has two heads – long and short. The biceps femoris is the only two-headed hamstring muscle. The long head is the one toward the outside of the thigh. It starts at the bottom of the pelvic bone. The short head originates on the femur, and thus is the only part of the hamstring group that doesn’t cross the hip joint. Put another way, the short head is the only part of the hamstrings that’s involved exclusively in knee flexion (or bending), with no role in hip extension. The heads of the biceps femoris attach to both lower-leg bones (tibia and fibula), on the outside of the knee.

Semitendinosus

The semitendinosus is a smaller muscle that starts on the lower pelvis (sharing a tendon with the biceps femoris) and runs alongside the biceps femoris before attaching to the tibia, on the inside of the knee. It gets its name because it has a long tendon of insertion. Unlike the biceps femoris, which inserts on the fibula, the semitendinosus inserts on the tibia. It is a two-joint muscle, so it both flexes the knee and extends the hip or trunk.

Semimembranosus

The semimembranosus is similar to the semitendinosus in location and action. The semimembranosus lies alongside the semitendinosus on the inside rear of the thigh, beginning and ending in the same places. It has a longer tendon at the top and a shorter one at the bottom. The only notable difference between the two is that the semitendinosus has a longer tendon and inserts on the front of the tibia whereas the semimembranosus inserts on the back of the tibia.

What Is the Purpose & Function of the Hamstring Muscles?

Like the majority of muscles of the lower limb, the hamstrings are vital to gait as well as a number of other body movements.

The primary functions of the hamstrings are knee flexion (bringing the heel toward the butt) and hip extension (moving the leg to the rear).

Their main roles include assisting in walking, running and jumping, as well as having a role in trunk support. The hamstrings also have a role in rotating the leg both internally and externally, however this role is minor. They also have a role in knee stability during both gait and stance.

More precisely:

  1. extension of the hip (long head of the biceps femoris, semitendinosus and semimembranosus, especially when the knee is extended);
  2. flexion of the knee (both heads of the biceps, semitendinosus and semimembranosus);
  3. outward rotation of the knee (both heads of the biceps) and the hip (long head of the biceps femoris);
  4. inward rotation of the knee and hip (semimembranosus and, above all, semitendinosus).

Best Exercises For Balanced Hamstrings

Because the hamstrings can produce three significant actions (extension of the hip, flexion of the knee, and outward and inward rotation of the knee), all those actions should be trained at some point.

The basic function of the hamstring is knee flexion. Exercises that train that movement are a variety of leg curls such as seated, prone, dumbbell, and ball leg curls along with the glute-ham raise (GHR), a more challenging variation.

The hamstrings (in tandem with the glutes) produce hip extension in such exercises as the squat, leg press, lunge, step-up, and reverse hyperextension exercises.

The hamstrings also cause trunk extension and are particularly emphasized when the knees are held relatively straight during this motion. Examples include the stiff-legged deadlift, romanian deadlift, and good morning exercises.

Any exercise that flexes the knee or extends the hips against resistance will work the hamstrings. Some of the best workouts include all varieties of:

  1. Leg curls (seated, lying, and standing)
  2. Stiff-legged deadlifts and Romanian deadlifts
  3. Lunges
  4. Squats, etc.

Despite the hamstring muscles arguably being the most important muscle group for athletes, they are often laggards in physique competitions. You may see an entire lineup of bodybuilders with massive upper bodies and thick quads, but few will have well-developed hamstrings.

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