Anatomy

The upper leg muscles provide your knees with mobility (extension, flexion and rotation) and strength. The hamstring muscles are located on the back of your thigh. They work closely with your quadriceps muscles (front of your thigh), your gluteal muscles, and your calf muscles to ensure proper movement of your leg and hip.

Your hamstring muscles control movement of your body, hip and knee, help turn your leg in and out, and are involved with power activities that include a lot of propulsion, thrust and control (such as jumping, running, and walking). They allow your knee to bend (flex the leg at the knee) and pull your leg backward while propelling your body forward when you move (your thigh straightens and extends the leg back at the hip). They are involved with eccentric movements, which increase the length of the muscle while it is under tension ­ instead of starting an action, the muscles act as a brake to stop an action. You can feel this when walking or running downhill, landing from jumps or performing squats, and when trying to stop quickly after sprinting.

The hamstrings (posterior thigh muscles) are made up of 3 long muscles that start at the bottom of your pelvis extending down the back of your thigh and along either side of your knee, to your shin bones. The lateral hamstring is the biceps femoris (made up of 2 parts - a short head and long head) and the medial hamstrings are the semitendinosus (joins the sartorius muscle and gracilis muscle at the pes anserinus on the tibia) and the semimembranosus (the largest hamstring muscle). The tendons (tough fibers that connect muscle to bone) for these muscles begin at your ischial tuberosity (the bony bump under each buttock, known as your "sit bone") and attach on the outer edges of your shinbone (your tibia and fibula) just below the back of your knee. They help to stabilize your knee. Your hamstrings also have a lot of soft connective tissues and are innervated by your sciatic nerve.

Pulled Hamstrings

Your hamstrings are very long muscles that cross 2 joints (your hip and knee) therefore they are more prone to injury. Pulled hamstrings (also called strained hamstrings) are one of the most common injuries in vigorous sports activities; 33% of lower body injuries for those between 16-25 years of age are hamstring injuries.

These occur when one or more hamstring muscles are stretched beyond their limit or are in a vulnerable position, and the muscle tissues become strained or torn. The biceps femoris muscle is the most frequently injured, as it suffers the largest stretch during sprinting, followed by the semitendinosus muscle. If you have a multi-muscle injury, it normally occurs at the point where your hamstring muscles and tendons meet (musculotendinous junction). However, they can also occur at any place along your hamstring muscle bellies, or at the tendon attachments to the bone.

Acute strains are caused by direct hit, fall or overloading, whereas chronic pulls are generally caused by overuse or prior unhealed injuries. The damage can range from overstretching to partial tearing to complete rupturing of the small fibers that make up your hamstring muscles.

These injuries occur most often early in the activity as a result of a poor warm up, or in the later stages of practices or games as a result of fatigue. Young, active teens or adults between 25-44 years are most susceptible to pulled hamstrings, and men are twice as likely to be injured as women.

Other common hamstring injuries involve hamstring contusions (bruising or hemorrhaging beneath unbroken skin), hamstring tendonitis or tendinopathy, or avulsion fractures (a severely pulled hamstring will tear a piece of bone with it). This generally occurs where the hamstring tendon attaches to the ischial tuberosity.

Weak hamstring muscles also play a role in knee or low back injuries (cause your pelvis to tilt). If you allow hamstring injuries to persist they can lead to repeated injury, periostitis (inflammation of the periosteum), and prolonged disability. They are often confused with sciatic neuritis.

Alternate names and/or associated conditions:

Hamstring pull, hamstring strain, strained hamstring, hamstring tendonitis, hamstring tendinopathy, hamstring syndrome, avulsion injury, posterior femoral muscle strain, hamstring tear, periostitis, hamstring muscle contusion, bursitis of semimembranosus or ishio-gluteal, chronic compartment syndrome of posterior thigh, hamstring scar tissue, sciatic neuritis, Myositis Ossificans