The sacroiliac joint typically has little motion. Small movements at the joint help with shock absorption and forward/backward bending. The joint is reinforced by strong ligaments surrounding it, some of which extend across the joint in the back of the pelvis. This network of soft tissues provides support, limits movement at the joint, and assists with absorbing pressure.
Often, a pulled or strained hamstring muscle can cause radiating lower back pain, and pain in the butt area as well. So, often, if you exercise a lot and are suddenly telling your friends, "My butt hurts a lot when I exercise it's likely because of a pulled hamstring. Often, a pulled hamstring can cause referred pain, such as upper thigh pain or upper calf pain and pain in the back of knee area as well. Symptoms of a pulled hamstring include severe pain during exercise and tenderness, pain in thigh muscles, sharp front thigh pain, and tenderness and bruising in the thigh area. The best pain reliever for hamstring pain is to use the RICE method explained above and to do stretches that relax the muscles of the thigh.
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.
How to do it: Stand up tall while holding onto a sturdy object like a chair, or rest your hands on a wall. Keeping your back straight and core tight, raise one leg up and lift it out to the side and away from your body, keeping your leg straight. Pause for one to two seconds, then return to the start position. That’s one rep. Repeat this movement, alternating sides each time.
Since someone has to do the job… (Side note: That’s one of the coolest things about our body. There is always a backup system. Always another set of muscles ready to take over. Even if they are not the most effective and it leads to pain and tightness.) So, who takes over for spinal stability when the abdominals aren’t fully working? The psoas of course.