**11. Hamstring**

The hamstring muscles are located on the back of the thigh and function to flex the knee and extend the hip. These muscles form the back and inside out of the thigh (semitendinosus, semimembranosus and biceps femoris (long and short head) the latter being the outermost of these muscles).

When this group of muscles are injured, the athlete reports having felt a "pull" especially when they are doing explosive exercises, and so the athlete stops and suspends all activity immedi‐ ately.

There are hamstrings injuries that can occur in a slow and chronic manner, so the symptoms are vague and can be confused with pain in the lower back; not all injuries to this muscle group are acute, [9].

The causes of this injury can be very marked imbalance quadriceps strength (muscle imbal‐ ance), also often are due to lack of elasticity or warm-up previous to ballistic sports activity [10].

When this injury occurs, pain is widespread, edema occurs quickly and the patient is unable to stand or walk on the injured leg. Moreover, in the course of a few hours a hematoma is present, which can be displaced by gravity towards the back of the knee.

On physical examination (with the patient lying prone) pain in the area of the tear is provoked by palpation and the patient cannot perform an isometric knee flexion or hip extension nor can the athlete perform hip extension (figure 19a).

**Figure 19.** a) With the patient facing down ask to rise the affected leg as high as he can; b) With the knee flex at 90° palpate al the hamstring muscle to locate the exact spot of the muscle injury

When the examiner bends the knee of the affected leg (to relax the hamstrings) palpation of the entire length of the hamstrings can locate the site and of the muscle injury (figure 19b).
