Poor posture can make you look 10 pounds heavier. It could sabotage a promotion. And slumped or hunched shoulders are a major reason why back pain affects 80 percent of Americans at some point in their life.

"Poor posture isn’t just disrespectful; it will ruin your spinal health and leads to a dreadful life," said Gloria Starr, an international business coach who teaches posture at her North Carolina finishing and etiquette school.

When your frame is aligned — meaning your heels, knees, pelvis and neck are stacked on top of each other — it moves more efficiently, can carry heavier loads, tires less easily and is less susceptible to strain or injury.

But the minute you sit down to update your Facebook page or drive to the store, you’ll likely drop your chin, tilt your head forward and round or hunch your shoulders. This pulls your muscles and ligaments out of balance — some muscles grow tight while others become weak — leading to back and neck pain, headaches, fatigue and other problems.

Still, it takes years to develop slouched shoulder syndrome and vulture neck, conditions that can’t be reversed overnight. Simply increasing physical activity doesn’t necessarily help; when a person with bad posture becomes more active it’s "like driving around with a crooked axle and hoping that the driving will straighten it out," said Esther Gokhale, founder of the Gokhale Method, which treats chronic pain through postural adjustments.

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THESE MOVES CAN HELP YOU STAND UP STRAIGHT

If you’re having pain, get your posture assessed by a physical or occupational therapist who can test muscle strength and flexibility, and can make adjustments to your work station if you have a sedentary job. The following exercises can also help strengthen the muscles that grow overused and tight.

The OJ squeeze:

When shoulders hunch, the muscles that stabilize the shoulder — the rhomboids and mid-trapezius muscles — become weak.

Try it: Pretend you’re holding an orange between your shoulder blades and try to squeeze it to make juice by bringing the shoulder blades (scapula) down and together, said physical therapist Paul Drew, the author of the book "Red Carpet Posture." Hold for 10 seconds. You’ll also stretch out the front of your shoulders, which may be tight from slouchy desk posture.

The shoulder roll:

Hunching the back forward compresses the front section of certain spinal discs and squeezes the contents backward, similar to squeezing one side of a s’more, said Gokhale, author of "8 Steps to a Pain-Free Back." "Over time, this action wears and tears the fibrous exterior at the back of the disc," she said.

Try it: Move one shoulder forward, upward and as far backward as you comfortably can without significantly moving your body. Gently slide your shoulder blade down along your spine. Your shoulder may settle further back than usual. Repeat on the other side.

The 5-minute rest:

The eyes are often overlooked when it comes to posture. Once they’re overused or fatigue, the head moves forward, taking us out of alignment, said Donna Eshelman, a Los Angeles-based Feldenkrais practitioner who teaches posture improvement to desk workers.

Try it: Lie on your back for five minutes. "Cup" your eyes by interlacing your fingers and placing the heels of your hands on your cheekbones and outer eyes to block out the light. This will help "oxygenate your fatigued muscles, improve breathing and restore your alignment," said Eshelman. Repeat once an hour.

Towel chest stretch:

To keep the shoulders from rounding forward, stretch out the chest muscles and strengthen the mid-upper back, said fitness expert Tracey Mallett, a Pilates instructor and personal trainer.

Try it: Stand tall with your legs shoulder-width apart, holding a rolled-up bath towel — one end in each hand, said Mallett. Keeping the bath towel taut, reach the arms forward at shoulder height. Exhale and pull the arms up and as far back as you can; you should feel a stretch in the pectoral muscles. Hold for two breath cycles and then return the arms back to shoulder height. Repeat five more times.

Plank:

Strong transversus abdominus muscles, which are the deep back and abdominal muscles closest to your spine, protect your discs and nerves from impact, said Gokhale.

Try it: Begin in push-up position, with your arms straight. Imagine a straight line from your legs through your torso to your neck. Don’t sag or lift your butt. If your shoulders are tensed toward your neck, roll them open, Gokhale said. Hold for up to a minute. This will "strengthen the muscles that keep your spine happy and lengthened," she said.

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DO DEVICES HELP?

"Ergonomic training," or teaching people how to sit at their desk, is one of the most common ways to improve posture. But can gadgets such as posture braces (think SkyMall magazine), posture clothing and even posture necklaces also help?

In general, postural supports or harnesses "can be a helpful reminder to not slump the upper body forward," said Esther Gokhale. The iPosture device, a microchip that clips to your shirt or a necklace and vibrates when you slump, could be useful for this as well, but there’s no evidence to show that it actually works.

The problem with many of the devices is "they don’t improve pelvic position, which is the key to sustainable, healthy posture," Gokhale said. "Ultimately, there is no product that can substitute for knowing what to do with one’s own body. Devices can only be useful in conjunction with an education in healthy posture."

One promising device, however, is a webcam that provides desk workers with pictures of how they currently look alongside a photo of their own correct posture. A study in the current issue of Applied Ergonomics found that use of the webcam, in conjunction with conventional training, resulted in sustained improvement. An effective intervention should be "a continuous process that provides frequent feedback," said the Israeli researchers.