Assessment and evaluation
Hamstring strain may occur as either an acute or chronic injury, but it is most likely to be acute. Consequently, the client is likely to report a sudden pain associated with some activity that overwhelmed the hamstrings. Due to the tensile loads on the muscle-tendon unit, it is common for the person to report hearing a loud pop or snap when the injury occurred.

Mild to severe pain occurs at the time of injury, and generally decreases over time. However, pain is easily aggravated if the damaged tissues are stressed. It is important to find out if the client has previously experienced a strain, because strains are likely to recur in the same location due to inflexibility of scar tissue in the area.

Several visual factors may help identify hamstring strain. Depending on the severity of the injury, the client may be limping or walking with some impairment. If the strain was in a highly vascularized region of the muscle, bruising is likely and may be extensive. With hamstring strain, bruising from the initial tear may look much worse after several days. Torn capillary beds leak blood into the interstitial spaces. Eventually gravity pulls the blood toward the feet and the bruised area becomes much larger and appears to run down the back of the thigh. In some cases swelling from the tissue-injury site may be visible, but often it is not.

Palpation is helpful for identifying hamstring strain. The hamstrings are likely to be hypertonic, resulting from reflexive muscle spasm. There is also likely to be exaggerated tenderness near the site of the tissue tearing. In second- or third-degree strains there is also a palpable defect in the muscle that feels like an indentation or disruption in the continuity of the fibers. In most cases there will be an exaggerated degree of tenderness at the site of the tear. The greatest number of hamstring strains occurs in the biceps femoris muscle, so palpation may reveal a problem toward the lateral side of the hamstring muscle group if it is not at the proximal musculotendinous junction.

Looking for pain or restriction during motion is an important part of the evaluation process. Pain may occur with active knee flexion or eccentric knee extension, as these actions engage the injured muscle (Figure 1). Pain and restricted range are also likely in passive motions that stretch the hamstrings, such as the common straight leg-raise position of hip flexion with knee extension (Figure 2).