Your quadriceps are located on the front of your thigh. Their job is to extend your knee and flex your hip. They are made up from four muscles: rectus femoris, vastas lateralis, vastas intermedialis and vastas medialis. These four muscles share a common insertion point in the quadriceps or patella tendon. Spending too much time sitting down or not stretching enough after working out can make these muscles tight. Tight quadriceps can cause knee and hip pain. One way to assess the tightness of your quadriceps is Ely's test.
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Remove your shoes and then lie on your front with your legs straight and your head resting on your arms. Position your legs so that your knees are together.
Tell your training partner to bend one of your legs and push your heel toward your butt. Stay relaxed so that your partner takes the full weight of your leg.
Bend the leg as far as possible until you meet resistance from the tension in your quadriceps muscles. Measure the angle of the knee joint using the protractor or the distance of your heel from your butt using the ruler. Make a note of the result.
Repeat the same assessment on the opposite leg. Compare the result from the left leg to the right to assess any flexibility imbalances. Ideally, both legs should bend to the same degree and your heel should touch or be very very close to your butt. The farther your foot is away from your butt, the tighter your quadriceps.