So how much of the 24 hr day do you spend with your hips flexed, knees bent and arms forward? A lot more than you thought right? We will begin by looking at the pelvis and the main muscle groups linked with lower back pain and our daily posture.
When we sit in a chair, sleep on our side; the hip flexor group and hamstrings are both in a short position. If we stay here for long periods daily, the muscles and fascia shorten and struggle to lengthen, fibres become misaligned, nutrients don't flow, tissues adhere to others etc. Likewise the gluteal group are in a long position, sustaining this for long periods can make it hard for the muscles to contract when required, bearing in mind that this group is the antagonist of the hip flexor group and contraction in 1 causes relaxation in the other (Reciprocal Inhibition). And this applies to those with a good seated posture too!
If the hip flexor group shortens there will be increased curve through the lumbar and anterior tilting of the pelvis leading to compression in the lumbar area.
The Psoas being the main muscle of the hip flexor group, it is linked directly to our fight or flight response (sympathetic nervous system) as we use this muscle to run, kick or curl into a ball and fascially linked to our diaphragm and therefore our breath. There is lots of interesting literature about this muscle and I could go on for hours! So I will keep it short and sweet, if the hip flexors are short the pelvis and spine are pulled forward when standing, in order to look where we are going, muscles on the back engage to raise our torso giving us the "duck waddle". Thus the abdominals are long and harder to activate. Sound familiar?
If the hamstrings become shortened they affect the tilt of the pelvis and the spine has to work harder.
The hamstrings attach to the sit bones (ischial tuberosity) on the back of the pelvis and if shortened can tilt the pelvis posteriorly. In this case the pelvis cannot tilt forwards freely, so upon bending forward the spine is required to move more placing more strain on the lower back. If you tuck your feet under your chair regularly they are shortening even more.