The hamstrings are the muscles that run down the back of the leg. Their susceptibility to injury makes them particularly interesting to athletes, coaches, personal trainers and sports medicine experts. Hamstring weakness, inflexibility or hyper-flexibility can alter your movement patterns, which in turn may cause injuries to other parts of the body.
Origins
While many anatomical terms are derived from Greek or Latin, the word "hamstring" comes from the old English word "ham" or "hamm," which referred to the back of a hog's thigh. The word "string" referred to the tendons. It has been speculated that the word was used to describe the way a butcher would hang the ham by its legs.
Features
The hamstrings are composed of three muscles; the semitendinosus, the semimembranosus and the biceps femoris. Their top attachment or origin is at the ischial tuberosity, which are the sitting bones in the buttocks. Their lower attachment, known as the insertion, is at two points: the tibia, which is the shin bone, and the fibula, which is the calf bone.
Function
The anatomy of the hamstring muscles defines their destiny or function. Their attachment to the hip and the knee gives them an active role in the movements of these joints. The semitendinosus and the semimembranosus, for example, cross the hip and the knee joint. They perform hip extension, knee flexion and medial leg rotation.
The biceps femoris, often called the leg biceps, have a long head and a short head. The long head, which crosses the knee and hip joint, extends the hip and bends the knee. In contrast, the short head of the biceps femoris only crosses the knee joint. As such, it is only involved in knee flexion. Both heads of the biceps femoris assist in lateral rotation of the leg.
Types of Hamstring Exercises
Exercises such as the seated, prone and standing variations of the leg curl work the hamstring muscles in the bending phase of the movement. The hamstrings also extend the hip during straight-legged dead lifts and back extension exercises.
Expert Insight
Strength training expert Charles Poliquin discusses the kinesiology of the hamstrings in an article on his bodybuilding website. He explains that the hamstrings are predominately composed of fast-twitch fibers, which means that they only have a minimal amount of endurance strength. He argues that performing more than eight repetitions on a leg curl machine requires most people to work at intensity that is too low to be beneficial.
Warning
The hamstrings are usually 60 percent to 80 percent weaker than the quadriceps, which are the muscles in the front of the thigh. This imbalance is exaggerated in some people. Weak hamstrings and quadriceps dominance may cause the knee to hyperextend when landing from a jump, thereby causing joint and ligament injuries.
Misconceptions
Many people think that they have tight hamstrings. They often actually have tight hip flexors. The hip flexors, which connect the thigh with the pelvis, work in conjunction with the gluteal muscles. Due to an anatomical process called reciprocal inhibition, when the hip flexors are tight, the gluteals become weak. The hamstrings, as mentioned, assist the gluteals in hip extension. When the gluteals are too weak for the task, the hamstrings must take on the entire workload. Stretching the hamstrings alleviates the tension, but it doesn't solve the problem. It's the hip flexors that need to be stretched.
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