Hamstrings

The hamstrings are not a single muscle, but a group of three muscles that lie alongside one another at the back of the thigh.

• Biceps femoris (biceps femoris) — Located on the outer side of the thigh. It has two heads: a long head and a short head.
• Semitendinosus (semitendinosus) — Located on the inner side, with a long, slender tendon extending from its lower end.
• Semimembranosus (semimembranosus) — Located deepest on the innermost side.

These three muscles generally share an origin at the sitting bone beneath the buttock (the ischial tuberosity), then pass the knee and attach to the tibia and fibula. Only the short head of the biceps femoris begins on the femur; the others are two-joint muscles that cross both the hip and the knee.

The Korean name is a direct borrowing of the English word “hamstring.” The name is said to come from a comparison between the firm tendons you can feel behind the knee and the strings butchers used to hang hams.

Because they span two joints, they have two main actions.

• Hip extension — They move the hip back and push the leg backward, bringing the thigh behind the body.
• Knee flexion — They draw the heel up toward the buttock.

When you walk or run, they also slow the forward-reaching leg just before it touches the ground, keeping the knee from straightening too far. This is why these muscles bear substantial force during sprinting and sports involving rapid changes of direction.

• A pulling sensation when bending forward — You may feel a pull at the back of your thighs when reaching your fingertips toward the floor while standing, or reaching toward your toes while sitting with your legs straight. The hamstrings are the muscles being stretched most in these positions.
• Stiffness after prolonged sitting — While you sit, your knees and hips remain bent, keeping the muscles in a shortened position for a long time. Many people feel tightness at the back of their thighs when they get up and walk.
• Working during running and stair climbing — They contribute to the force that pushes the ground backward when you run and lifts your body upward when you climb stairs. They work together with the Gluteus maximus, a buttock muscle.
• A sudden effort can catch them off guard — Sprinting or kicking for the first time in a while can sometimes cause a startling sharp, electric sensation or a sudden knot at the back of the thigh. These muscles often take on a concentrated load during fast activities such as running.

The Quadriceps femoris at the front of the thigh straightens the knee, while the hamstrings bend it. By acting in opposite directions, they help the knee move steadily. The Gastrocnemius in the calf also assists with knee flexion.

• Warm up before exercise — Loosen up with light walking or jogging in place, then use dynamic stretches such as large forward-and-back leg swings to help the muscles begin moving smoothly.
• Stretch while lying down — Lie on your back, raise one leg, loop a towel or band around the sole of your foot, and pull gently. Hold for 20–30 seconds at a comfortable stretch at the back of your thigh, and keep breathing easily. See Passive stretching for the method.
• Stretch by contracting and relaxing — While holding the stretch, gently push your foot against the towel, relax, and then stretch a little farther. Many people feel that this lets them stretch further. The principles are covered in Muscle energy technique and PNF stretching.
• Build strength — Exercises that involve slow, controlled effort, such as the Deadlift, in which you bend forward while moving your hips back, or the Nordic hamstring exercise, help strengthen these muscles.
• Change your sitting position — If you have been sitting for a long time, get up and walk about once an hour, and stretch the backs of your thighs while standing.
• Increase exercise gradually — Rather than suddenly increasing your running speed or distance, try increasing it a little each week.

If you hear a “pop” at the back of your thigh during exercise or feel sudden, sharp pain, you may have injured a muscle or tendon. If this happens, stop exercising and rest. Consult a healthcare professional if walking is very painful, you develop extensive bruising, or symptoms do not improve after several days. Above all, after an injury, it is best not to return immediately to full effort just because the pain has settled. Instead, build up gradually, starting with walking and light exercise.