The ‘Sit’ Bones and Your Back
Many things happen bio-mechanically while you're sitting, even if you have great posture, but less so when you optimize the distribution of forces. The main thing to consider is what you're sitting on, not just the seat, but your body. Those two bones, the ischial tuberosities or 'sit bones' are just at the bottom of the pelvis - the ischium. They protrude a bit so they're easy to feel and find whether you're standing or sitting. We're always guided to sit right on top of them because that will balance the pelvis and line the spine up on top of the sacrum, the tailbone of which is right in the middle of the sit bones. Many muscles attach to these sit bones, namely, the adductor magnus, gracilis, and hamstrings at its apex, while the gemellas, obturators, and quadratus femoris attach on the sides of these bony protrusions. They rotate the hip as well as extend it. Hip flexors, like the psoas muscle are also involved, but we don't sit directly on them. The sacrococcygeal ligaments that connect the back of the greater trochanter with the tailbone help to stabilize the apex of the sacrum, and just a little slumping in a chair will put a great deal of pressure on these guys. Just at the tip of the tailbone lies the attachment of fibers that connect to the sheath surrounding our spinal cord which travels all the way up to the head and wraps around the brain - the dura. So sitting can tighten your thighs, your hip joints, your pelvis, your back, and even give you a headache.
In an earlier post some suggestions were made on how to stretch and open out the upper body from sitting with arms forward and chest dropped, and this one will recommend opening out the lower body after sitting - or before and after! With any new exercise, it's important to go slowly and gradually into requesting that your muscles adopt a new position, introducing the idea and allowing time for the body to agree with you on the change. If your knees don't make it all the way to the floor initially, that's fine. Just start from where they comfortably do reach and gently press down on them thinking about the bones moving rather than thinking about stretching the muscles. When you focus on the position of the bones, the muscles know they need to adjust themselves in order to allow the bones to move to a new place and it doesn't engage the stretch reflex like focusing on muscles may. In any case, keeping these interior and posterior muscles that attach directly to your pelvis have a huge effect on the ability of your back muscles to remain relaxed. They will be take more pressure off your back than working directly on the back muscles will. That being said, a long line of thoracic back muscles get triggered by stress, and in this case massaging them will be helpful.
The sacrum plays an important part of the spine being able to hold gravitational forces optimally. If one of the SI joints becomes stuck or rotated, it could be very uncomfortable and even trigger sciatica. A simple exercise to help stabilize and balance the sacrum - again, approach it delicately if you haven't been in this position for a while. We all use it when we're toddlers, but over time if the thigh muscles are tight or the feet cause gait issues, the knees may not allow a full squat. So drop down only as far as is easy and comfortable and give a moment for the low back to ease down and decompress as well. Then do a very gently press out with your elbows from the inside of your knees. Just hold it for half a second, then place your arms outside of your knees and press out with the knees - also very lightly and briefly. This will facilitate balance and ease in the sacro-iliac joint and its relationship to the surrounding ligaments and muscles, as well as with the hip joint. Doing these exercises for just five minutes after your work day will give you energy for the rest of the day, release cumulative tensions, and help you to sleep better and awake without feeling stiff or sore.