Muscle:

Biceps femoris (two heads: long head, short head)

Origin:

The long head originates at the ischial tuberosity and sacrotuberous ligament (at the base of the pelvis in the groin area).

Insertion:

The long head inserts into the lateral side of the fibula and tibia (below and to the outside of knee)

Function:

The biceps femoris, because of its location on the femor, is sometimes referred to as the “lateral hamstring.” It has two heads: the long head and the short head. Since the long head crosses both the hip joint and knee joint, it extends the thigh as well as flexes the knee. The long head works in conjunction with the short head to laterally rotate the foot outward when the knee is semi flexed (hip-leg-outward rotation and slight adduction).

Muscle:

Biceps femoris: short head

Origin:

The short head originates at the lateral side of the femur.

Insertion:

The short head inserts at the lateral side of the fibula and tibia.

Function:

The short head does not cross the hip joint (unlike the long head), only the knee joint and therefore is only involved in knee flexion. It also works in conjunction with the long head to laterally rotate the foot outward when the knee is semi-flexed.

Muscle:

Semimembranosus (most medial hamstring)

Origin:

At the ischial tuberosity (base of pelvis in the groin area)

Insertion:

The medial tibia

Function:

Since the semimembranosus crosses both the hip and knee joints, it extends the thigh, flexes the knee and medially rotates the foot inward. The semimembranosus and semitendinosus are known as the “medial hamstrings”.

Muscle:

Semitendinosus 

Origin:

At the ischial tuberosity

Insertion:

The medial tibia

Function:

Since the semitendinosus crosses both the hip and knee joints, it extends the thigh, flexes the knee, medially rotates the foot inward, and creates hip-leg adduction. The semitendinosus and semimembranosus are known as the “medial hamstrings”.

Indications of Weakness:

If hamstring weakness is on one side, it may present as an anterior rotation of the hip bone (technically: the hip bone is referred to as the “innominate bone”, made up of the iluim, ischium and pubis). When you assess the athletes hip levels by putting your hands on the top of the standing athlete’s ilium, the pelvis will appear relatively higher on the affected side. You may also notice a shift to the stronger side while the athlete performs any squatting or dead lift type movements.

Weak hamstrings will result in tearing of the hamstring during sprinting activities. Female athletes experience ten times the amount of hamstring tears as a result of weak hamstrings and the imbalance of strength between the quadriceps and hamstrings (this is due to the agonist – antagonist relationship). The hamstrings must have at least 75% of the strength of the quadriceps in order to maintain an optimum balance. Weak hamstrings present as medial rotation of the knees during squatting movements.

Weakness of the biceps femoris can cause your athlete to have “knock-knee” (Genu Valgum), due to the medial rotation of the thigh and tibia. This can be corrected by performing leg curls with toes pointed outward. You can verify your suspicions by watching your athlete’s feet the first time they perform a lying leg curl. Since the gastrocnemuis aids with leg flexion, most inexperienced weight trainers will perform a leg curl with the foot in dorsi flexion (toes curled upward toward the knee).

If your suspicions are correct on weak biceps femoris, the feet will dorsi flex and the toes will rotate inward (toes together). The weight trainer is naturally utilizing the stronger medial hamstrings. Correct this weakness by forcing the weight trainer to point the toes-rotated outward during leg curls 

If the medial hamstrings are weak you will observe the exact opposite: toes will point outward while the foot dorsi flexes. You may also observe your athlete walking and standing “bowlegged” (Genu Varum) due to the lateral rotation of the thigh and tibia. You will correct this by forcing your weight trainer to point the toes inward to increase the stress on the medial hamstrings.

Optimal Training Principles:

Hamstrings are made up of mostly Type IIB, fast twitch muscle fiber and are used for sprinting and power work. In order to gain size and strength in the hamstrings you are going to need high intensity training. Heavy lifts of 8 RM or heavier, speed work: such as sprinting and plyometric exercise and other high intensity strength, speed or power exercises will develop the hamstrings.

Since the hamstrings have two major functions: thigh-hip extension and knee flexion, you will need to train with two groups of exercises. Lying, seated, standing and stability ball variations of leg curls will stress the leg flexion function of the hamstrings. While back extensions, reverse hypertensions (just the title of the exercise-no one here is suggesting you hyperextend your back or any other body part), Romanian dead lifts, single-leg-stiff-knee dead lifts, and other variations to stress the thigh-hip extension function.

The stability ball leg curl exercises and single-leg-stiff-knee dead lifts (support leg knee is held at a 10 - 15 degree bend throughout the exercise. Use dumbbells held at the sides of the leg to eliminate torsion shear forces on the low back and hip) are not only great hamstring developers, performed correctly they are excellent for core development.

You can increase stress to the biceps femoris by pointing the toes out during leg curls. You can increase stress to the semitendinosus and semimembranosus by pointing the toes in during leg curls.

James T. Bell, PhD.c. is the founder and president of the International Fitness Professionals Association, IFPA.

More Books from Jim Bell, PhD.c.

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