The three muscles that will flex the hip are the: iliopsoas, rectus femoris and then sartorius. These muscles have importance for executing a curl-up/sit-up and many other movements that involve hip flexion. For example, if you were to lift your leg in a bent position and bring your knee towards your chest like you are marching, that is hip flexion. Basically, you are coming from a starting neutral position (180 degrees) and bringing your bent leg to a 90 degree angle. You have decreased the angle, and when you decrease the angle of a muscle it is in flexion. When you increase the angle of a muscle, you are practicing extension.I mentioned the iliopsoas muscle and it is named this because the psoas major and the iliacus are closely related, so we call it the iliopsoas muscle. When looking deeper into this area of our body, the psoas major is attached to the lumbar vertebrae (L1, L3, L4 and L5) of the transverses, body & discs of the lumbar vertebrae. When we use this specific muscle we pull the lumbar vertebrae forward, so it is not a good idea to exercise this muscle in a ballistic or violent type of motion. These muscles are really deep into the hip, so when they get aggravated it can be very painful to release them and requires extremely deep massage in the form of ART or rolfing.When looking at the rectus femoris, this is the only muscle that crosses the hip and acts on the hip. It attaches to the anterior inferior spine of the iliac spine of the ilium. In addition, it attaches to the tip of the scapula and patellar ligament of the tibial tuberosity.Lastly, when we look closely at the sartorius, this is on the anterior-superior iliac spine to the anterior medial condyle of the tibia, which is also used as a hip flexor.
I know this is a little in depth, but just in case you wanted to know, here it is.
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