Subjects with tight hamstrings will receive dry needling to the hamstrings with the needle inserted into the muscle tissue in addition to a standard hamstring stretching exercise program.

Subjects with tight hamstrings will receive sham dry needling to the hamstrings with the needle inserted into the subcutaneous tissue in addition to a standard hamstring stretching exercise program.

Subjects with tight hamstrings will receive no needling but have the tip of a blunt needle handle placed on the skin over the hamstrings in addition to a standard hamstring stretching exercise program.

Dry needling will be performed on two points over the hamstring muscles on the randomly determined side. Points 2 cm distal to the ischial tuberosity and halfway between the ischial tuberosity and popliteal crease within the medial and lateral muscle bellies will be identified and the skin cleansed with rubbing alcohol. A Seirin L- type 50 mm needle will be inserted into each of the two points to a depth no greater than three-quarters length of the needle into the hamstring muscle for 30 seconds using a vertical pistoning technique and then statically up to 10 minutes.

Bilateral 90/90 hamstring muscle extensibility passive range of motion (PROM) measurements will be assessed using a goniometer. The goniometer measures the angle of the joint at both extremes of the range of motion (ROM). An increase in the passive range of motion (PROM) indicates increased hamstring muscle extensibility.

The functional performance of the hamstring muscles will be assessed by using the unilateral hop for distance test. The subjects will be instructed to stand on the leg to be tested and hop and land on the same limb. The distance hopped, measured at the level of the great toe, will be measured (centimeters). Scores will be recorded as absolute distance (in centimeters). An increase in the score (distance covered) from baseline to 5 weeks from baseline indicates better functional performance of the hamstrings.

The functional performance of the hamstring muscles will be assessed by using the crossover hop for distance test. The subjects will be instructed to hop forward 3 times while alternately crossing over a marking. The total distance hopped forward will be recorded. The heel of the hop leg will be used to determine the length of the jump. Crossover hop limb symmetry index (LSI) scores for knee function within normal ranges are generally greater than 95%. An increase in the crossover hop limb symmetry index (LSI) from baseline to 5 weeks from baseline indicates better functional performance of the hamstrings.

The strength of the hamstrings will be assessed using a hand-held dynamometer.The subjects will be asked to exert maximal force against the dynamometer and the reading is recorded. Scores are based on force production in kilograms or pounds; kilograms (0-90), pounds (0-200). Higher pressure scores indicate better muscle strength of the hamstring muscles.