Hamstring muscle is present on posterior region of thigh starting from gluteal region and ending in popliteal fossa. Hamstring has three muscles biceps femoris, semitendinosus and semimembranosus causing flexion at knee joint and help in extension of thigh. Biceps femoris further consists of two heads (long and short head). Long head is supplied by tibial part of the sciatic nerve, while short head is supplied by the common peroneal part of the sciatic nerve. Muscles such as gastro-soleus, tibialis posterior, rectus femoris, iliopsoas, tensor fasica lata, the hamstrings and hip adductors are more likely to be tightened in lower limbs. Muscle tightness can cause the muscle shortness and does not allow full passive or active range of motion. Full active and passive range of motion is only achieved when muscle is flexible.

Tightness of hamstring muscle can occur due to many reasons like injury to the muscle, prolonged sitting hours which are part of different jobs and educational setups. This tightness could lead to strain of the hamstrings, which is the most common occurring injury of the lower limbs. Moreover, hamstring tightness is also correlated with low back pain and lumbar dysfunction. Massage and stretching relax the tightened muscles but cannot normalize the tone or improve their coordination. To achieve this, investigator retrained muscle memory by actively using those respective muscles. Simple stretching of different muscle groups especially hamstrings has been found to improve the extensibility and length of shortened muscles.

Additionally, muscle Energy Techniques (MET) and their related post-isometric relaxation techniques have demonstrated better results in improving flexibility of the tightened muscles. Muscle Energy Techniques are used in soft tissue pathologies in which the patient performs active muscle contraction in specific positions and in specific direction against a force applied by the therapist. The therapist guides and controls the movement with instruction. These are manual techniques that use contraction of the specific muscles and are found to be effective in increasing flexibility of the muscles and improving range of motion. The underlying mechanism through which improvement in extensibility and length occurs is yet unclear and thought to be attributed to both mechanical as well as neurological factors. Firstly MET techniques applied to increase extensibility of the muscles typically involves following steps: stretching the muscle to the limit of barrier or person's tolerance, secondly the person performs an active isometric contraction of the muscle being stretched against a controlled resistance provided by the therapist, additionally the person relaxes the muscle being stretched while the therapist continues holding the stretched position, furthermore the therapist takes up the new range produced by muscle and lengthens it up to a new barrier, and this whole procedure is repeated again according to defined guidelines. The MET techniques can be modified with variations in different components such as force of contraction, duration of the contraction, duration of the stretch and repetitions. This whole process results in increased range of motion and improves flexibility.

Post Isometric Relaxation (PIR) is a type of MET that relaxes the tight muscles with avoidance of initiating stretch reflex. This in turn results in reduced spasm and improved ROM. The relaxation is induced due to isometric contraction of the muscles with facilitation and inhibition. Active Isolated Stretch (AIS) is another type of stretching in which specific movement is performed for a specific muscle with assistance from a therapist or self-assisted (with rope or a band) and those particular movements are repeated again and again to induce a relaxation phenomenon in muscles, fascia and connective tissues. In AIS, movements are monitored carefully to avoid producing any stretch reflex .

A single blind randomized control study was done in Islamabad federal college Islamabad with the duration of 6 months from Jan 2018 to July 2018.the calculated sample size was 35 students (17 in group A and 18 in group B) through open epi . Non probability random sample selection method was used on the behalf of inclusion and exclusion criteria. 22.2+ 2.02 year male and female students of DPT with tight hamstring were included while hamstring injury and any neurological or orthopedic disorder were excluded. The study was approved by the Ethical and Research Committee, and all participants signed the informed consents. Group A was given post isometric relaxation while Group B was given Active isolated stretch for a period of 3 weeks. Outcome measures were assessed at baseline, after first and final exercise session to estimate immediate and short term effects while long term effects were calculated after two weeks of final session of interventions. Semi structured questionnaire was used for subjective and objective assessment. AKE score, sit and reach test score and Lower Extremity Functional Scale questionnaire was used to assess lower extremity functional activities. Sit and reach test was also used to measure hamstring length.