A posture strap is a device that is worn under the clothes for the purposes of improving posture. This item will not be prescribed by a doctor, as a back brace will. Instead, a posture strap may be purchased in some fitness stores or online, is fitted by the individual who purchases it, and is typically made up of a series of cloth straps. Some people find that this can be a helpful way to improve posture or to sit more comfortably at a computer all day.
Clothes are worn over the posture strap, but undergarments are worn under it. It typically features two straps that go over the shoulders, forming an "x" in the back. When the posture strap is worn, it helps to pull the shoulders back, open the chest, and straighten the spine. This is because the "x" of the posture device will typically press into the thoracic spine, the area of the spine in the upper back where a rounded appearance can occur due to poor posture or sitting slumped at a computer.
A posture strap is useful for correcting mild or moderate postural problems that are not caused by any true spinal deformity, such as kyphosis or scoliosis. In those cases, a strap will generally not have any effect on the condition. Those cases typically require treatment from an orthopedic doctor, and may require an actual rigid posture brace, physical therapy, or even surgery in order to correct the problem.
Keep in mind that a posture strap may be worn for postural support, but it is no substitute for exercise and practicing good posture on one's own. It is necessary to strengthen the muscles in the abdomen as well as the back in order to have good posture. A strap can help retrain muscles that have become tight, or pull back shoulders that have become rounded, but unless the muscles are exercised, they will simply stay weak and will go right back into the poor postural position once the strap is removed.
It is best to wear the strap only as much as necessary until the posture improves. Practice good posture by sitting up straight at one's desk, with the shoulders back, and be sure to get up regularly to take breaks and walk around. A posture strap is made to be unnoticeable under clothing. It is also necessary to wash it regularly, since it will be up against the skin whenever it is worn.