According to a 2019 national survey, 47 percent of people in the USA say they are concerned about their posture and its impact on their health.

Even though slumping over in a desk chair and walking around with rounded shoulders may feel more comfortable, and easier, than learning the best way to correct your posture, it's not doing your health any favours. Slouching can make you feel fatigued when you're simply sitting, lead to headaches and pain, or cause numbness and tingling in the legs and arms. When you're sitting for longer periods of time, you also start leaning forward and compressing the diaphragm. You then won't be getting proper air and oxygen, which is part of the reason why we feel fatigued.
​
But it can also lead to more serious health implications — slumping over can wear away at the spine, making it more  prone to injury, cause back, neck, and shoulder pain, decrease flexibility and misalign the entire musculoskeletal system, according to the U.S. National Library of Medicine (NLM). Why? Think of your head like a 5 kilogram bowling ball — when you lean forward, the gravitational pull on the head increases, which can cause the weight of the head to put up to 5 times that amount of pressure on your neck and shoulders. Even a slight misalignment can place unnecessary strain on your body.

7 points to consider when standing upright:

Step 1: Start standing with feet shoulder width apart. Distribute weight equally on the balls of both feet.

Step 2: Gently pull your lower abdominal muscles up and in, as if moving the belly button toward the backbone, to achieve a neutral spine. (Another way to picture this is to imagine slightly tucking the stomach in.)

Step 3: Gently lower shoulder blades back and down as if tucking them into your pants pockets.

Step 4: Adjust your body so knees are pointed forward and relaxed or slightly bent. Align your knees over feet, hips over knees, and shoulders over hips.

Step 5: Let arms hang naturally at your sides.

Step 6: Look straight forward and keep your head level so that earlobes are above shoulders. Avoid pushing your head forward, backward, or to the side.

Step 7: Scratch the crown of the head to bring awareness there. Picture an arrow shooting straight upwards from that point on the head. This visualization will help in lifting the chin so that it is parallel to the floor and in ensuriing that your body is standing tall.

Poor posture contributes to problems in breathing patterns. We see this issue frequently in people who spend a lot of time sitting each day. Maintaining a posture where your shoulders are rounded and your head is forward causes the muscles around your chest to tighten. These tight chest muscles can limit the ability of your rib cage to expand, and this can cause you to take rapid, shallow breaths.

More specifically, people with a more curved upper back (thoracic kyphosis) and internally rotated shoulders have limited movement of their thorax. When breathing in, the rib cage can’t fully expand and the lungs cannot fully inflate.

An increased arch in your lower back (lumbar lordosis), where the pelvis is tilted forward, decreases the range of motion of the lower lumbar spine and shortens the latissimus and lower back extensor muscles. This limits the range of motion of the diaphragm, again restricting the inflation of your lungs. The abdominal muscles are overstretched in this posture as well, limiting their function of helping to breath out. 

Some people may also find difficulty breathing with an exaggerated curve in their neck (cervical lordosis) due to compression of their larynx. 

Belly breathing pulls down on your diaphragm, which is a dome shaped muscle between your chest and your stomach, to suck air into your lungs. Belly breathing fully inflates your lungs so that you get as much air as possible, whereas chest breathing only partially inflates your lungs.

Stress-related illnesses, sleep problems, respiratory problems, immune system weakening, and high blood pressure are all symptoms of long term shallow breathing.
 
Try it for yourself
While sitting in a chair, let your shoulders slump and your head hang forwards. Now in this position try and take a deep breath.

How does it feel? Hard to do a belly breath right?

Poor alignment in that slumped position means your diaphragm can’t descend easily making it hard to activate the posterior half of your diaphragm that attaches to your lower ribs and spine. To get enough air in, your body has to recruit its “back up” breathing muscles around the neck and chest to help breathe in, expanding the rib cage to get air travelling down into the lungs.

These neck and chest muscles are not very efficient and are not designed to be used for the 17,000 breaths we take on average per day. They get tired, fatigued and tight, which can lead to headaches, neck and jaw pain.

Now try sitting tall, with your head up and shoulders back, then take a deep breath into your belly. It’s easier, right? The process of putting yourself in a more optimal position for your spine allows the correct respiratory muscles to activate, drawing air into the lower lobes of the lungs where the best bloody supply is. 
  
*Clinical research findings*
Forward head posture causes expansion of the upper thorax and contraction of the lower thorax, and these morphological changes cause decreased respiratory function.
(JOURNAL OF PHYSICAL THERAPY SCIENCE 2019)

Results indicate that forward head posture could reduce vital capacity, possibly because of weakness or disharmony of the accessory respiratory muscles.
(JOURNAL OF PHYSICAL THERAPY SCIENCE 2016)

Alteration of head and neck positions can have an immediate negative impact on respiratory function. Clinicians should be prompted to assess respiratory function when assessing individuals with forward head posture and torticollis and reduce the tension on respiratory system to avoid negative consequences.
​(BIOMED RESEARCH INTERNATIONAL 2018)