Poor posture can lead to back pain by causing problems with your intervertebral discs and joints, as well as your muscles.
Poor posture can place stress on your spine that can lead to anatomical
changes in the spine such as shifting of discs and adjustments to the
natural curvature of the spine. These changes can ultimately cause back
pain due to the constriction of blood vessels and nerves, causing pain.
For example, standing or sitting in a position with your neck tilted too
far forward for prolonged periods of time (common when using a cell
phone) can add extra weight on the vertebra and strain the trapezius
muscles, which can result in a change to the natural curvature of the
spine. In other cases, such as sitting for long periods of time with
poor posture, extra weight from the upper body can be placed on
intervertebral discs of the lower back while they are unsupported. This
uneven distribution of weight can result in pain caused by disc bulging
in the spine and pinched nerves.
Additionally, with
prolonged poor posture, muscles can become tightened and overstretched,
leading to muscle fatigue and stiffness, causing pain. For example,
standing for long periods of time with your weight more on one foot than
the other can place extra pressure on one hip, which can overburden the
muscles in the lateral hip region, causing them to tighten, while the
muscles in the buttocks weaken. Over time, this will result in the
development of muscle imbalances in the pelvic area, resulting in muscle
strain in the lower back and causing pain. Similarly, a common poor
posture position in which a person is "stooped", or stands with their
pelvis tucked in and their back flat instead of naturally curved,
creates muscle imbalances and a misalignment of the spine resulting in
muscle fatigue and pain in the neck and back.
An intervention study is a type of controlled clinical trial in which an intervention is applied to a group of people and the outcome is compared to a similar group without the intervention. An example of this type of study is shown in the question above, where a margarine which vegetable ingredients (which is the intervention) will be given to a group of people, so that their blood cholesterol levels are compared to the cholesterol levels of a group of people who didn't use this margarine.
