Posture affects how you feel and how your body functions. Here’s how to get it right.

Even with all the talk about good posture, it is rarely defined. Posture is the position in which you hold your body. “It is a balance between the muscles and structural elements of your body, including ligaments, bones and discs in your spine,” says Dr. Afshin Razi, vice chair and residency program director of orthopedics with the Maimonides Medical Center in New York. Most importantly, “posture is something you can reverse,” he says. This is different from structural changes to your spine, which may require medical intervention.

Sitting matters. “While correct posture when standing is key, posture when seated is just as important,” says Dr. Razi. “We know that sitting posture can help prevent or lessen back and neck pain,” he adds. “Be sure your back and bottom are all the way against the back of the chair.”

Check out these simple moves to maintain good posture while sitting and standing.

Switch it up. “Your spine doesn’t like to be in one place for more than 20 minutes,” says Dr. Razi, “as it puts pressure on your disks. It is important to reposition yourself to reduce pressure, even if it’s just getting up for a minute then sitting back down.”

Focus on the core. Good posture is about the position of the spine but the surrounding core muscles are equally as important. Bad posture can stress core muscles but weak core muscles can also make it easier to succumb to poor posture. When Dr. Razi sees patients, often, the first line of attack is to strengthen the core through physical therapy. “If you have bad posture, you’re stressing those muscles more,” he says. “Your muscles have to work harder to maintain that posture.”

Check out this guide to functional fitness that can benefit your core.

Early years matter. Dr. Razi now sees teenagers that are experiencing structural changes in their spine because they spend so much time hunched over phones and other devices. “When your head is tilted forward, it adds a lot of stress on your shoulders and upper spine,” he says, adding that bad posture in the early years can cause structural problems that need medical attention. Correcting posture early in life can make a difference.

“There’s a reason we’re upright,” he says. “Any deviation stresses your structure. You can be in a bad posture for half an hour, but if you do it for hours and hours that’s when back pain occurs.”