Apply the above concept to your hips. When you sit, your hips are in a "flexed" position. Therefore, the muscles that flex your hips are in a shortened state. You probably spend at least a third of your day sitting down. Think about how much time those hip flexor muscles stay shortened. A lot. Over time, they become tighter and tighter until you look like the old man in the picture. So unless you want to look like that, perform the stretches shown below.
When a muscle contracts, it shortens. Take the biceps for example. Without getting too technical, the biceps are attached at the forearm and shoulder. When your biceps contract, they shorten and bring those two points closer together. When you rest, the muscle returns to its normal length, and the two points move farther away. Constantly contracting your biceps over a long period of time would cause them to get shorter, even at rest.
Think about keeping your head over your heart, and your heart over your hips, and don’t allow an excessive curve in your back. Keeping this correct posture will ensure you’re doing the stretch right. Squeeze your glutes as tight as you can, keep your back tall, and lean forward slightly. One to two inches should be enough! You should feel this in the front part of your hip on the leg that’s underneath you. Switch legs after 30 seconds or so; repeat as desired.
The illiacus attaches on the upper portion of the femur and begins on the inside crest of the illium (inside of the pelvis), where the psoas attaches all the way through the transverse processes of the lumbar spine, even binding into the discs directly. The rectus femoris begins at the base of the anterior superior illiac spine, and attaches all the way down to the knee cap, whereas the sartorius starts in the same place as the rectus femoris, but attaches on the medial aspect of the knee, blending with the MCL and portions of the hamstrings.
2) The athlete or client will use the TFL and the other ischial hip flexors to flex the hip. In this case the athlete or client will begin to complain of a low-level strain in the TFL. This is a result of overuse of a synergist and will feed into a synergistic dominance of the TFL and further psoas and iliacus dysfunction. This is what we have classically seen in our hockey athletes who utilize a flexed posture.
Of course, you know what it feels like to have a tight muscle. But tight hips aren't just uncomfortable—they can lead to all sorts of other aches and pains, especially in the lower back. "People focus on the hips and say their hips are tight, but we don't always think about the fact that the lower back connects to our legs at the hip," Charlee Atkins, C.S.C.S., instructor at Soul Annex in New York City and creator of Le Stretch class, tells SELF. Tight hip flexors make it harder for your pelvis to rotate properly, which can cause your lower back to overcompensate, "and this can be a setup for lower-back injury," Teo Mendez, M.D., an orthopedic surgeon at NY Orthopedics who focuses on operative and non-operative management of sports-related injuries, musculoskeletal injuries, and arthritis, tells SELF.