1. Sore Muscles:
The most common effect of poor posture are sore muscles. As you slouch, the muscles have to work harder to keep the spine stabilized and protected. The extra work on these muscles can cause muscle tightness, pain, and fatigue. This can lead to chronic issues with tight, painful and sore muscles from the neck all the way down to the lower back. Two major muscle groups that bare the brunt of these issues are the flexors and extensors of the trunk, which allow you to bend forward and lift objects. Overworking these muscles aren't good while they can also lead to spinal curvature due to the pressure.
2. Spinal Curvature:
This is one of the most serious issues that can occur with bad posture, developing a spinal curvature. According to the Chiropractic Resource Organization, the human spine has four natural curves that make up an "s" shape (Picture and definition in "What is an Actual Good Posture" on the categories bar to the right). When bad posture is practiced, the spine may experience pressure, which slowly influences the spine curves and changes their positions. The spine is specifically designed to help absorb shock and keep you balanced, but as the spinal position changes, this ability becomes compromised. If you start having a habit of being in bad postures for a long time, when you grow old, you may develop permanent spinal curvatures (leading to subluxations), making it hard for you to bend.
3. Subluxations:
Once the spinal chord is curved and altered, one major issue that can occur are subluxations. Vertebral subluxations occur when a vertebrae become misaligned from the rest of the spine. This affects the overall integrity of the rest of the spinal column. These misalignments can eventually cause chronic health problems including stress and irritation of surrounding spinal nerves.
4. Blood Vessel Constriction:
As bad posture changes the alignment of the spine, the resulting changes and subluxations may cause problems regarding blood vessel constrictions. The constriction of the blood vessels around the spine can cut off blood supply to the cells of the muscles, which can affect nutrient and oxygen supply. Blood vessel constriction can also raise your chances of clot formation and issues with deep vein thrombosis.
5. Nerve Constriction:
One of the most common side effects of a bad posture is nerve constriction. As the spine curves in shape, the resulting changes or subluxations can put pressure on the surrounding spinal nerves. Since the nerves that connect to the spine come from all over the body, these pinched nerves can not only cause neck and back pain but may also cause pain in other unrelated areas of the body.
6. Deepens depression:
Bad postures not only has effects in the physical health you are in. In a recent study from San Francisco State University, an experiment asked the students to either walk down a hall in a slouched position or to skip. The slouchers reported increased feelings of depression and lower energy than skippers. This psychological behavior is another reason for you to avoid being in bad postures.
7. Social Problems:
Bad postures also affect the way other people view you. Being in a bad posture doesn’t just hurt your attitude—it can affect how people see you. “You don’t want to walk into somebody’s office slouching and bent over, because people really do perceive you as not as vital,” says Janice Novak, author of Posture, Get it Straight. Your postures is a sign of your status sometime, with a great posture, you give out the signs that you are a confident successful person while vise versa, having a bad, slouched posture can give signs that you are a lazy or unconfident person.

Sources:

http://whatsyourposture.com.au/posture-health/

http://www.prevention.com/health/healthy-living/how-bad-posture-affects-your-health-and-happiness/2-causes-career-problems

http://www.livestrong.com/article/31223-negative-effects-poor-posture/

In contrast to the popular belief, a good posture does not mean keeping your spine completely straight. Many people has this misconception and it will deter them from keeping a good posture since it was just so tiring having to have their backs so straight all the time. If you feel it is exhausting whenever you try to maintain a good posture, it’s probably because you are trying to keep your back fully straight. Trying to keep your back/spine fully straight is actually as detrimental to your back as a slouched posture. By constantly tightening your back muscles, you end up straining it in the process.
A good posture means maintaining three natural curves at your back –

• An inward or forward curve at the neck (cervical curve)
• An outward or backward curve at the upper back (thoracic curve)
• An inward curve at the lower back (lumbar curve)

When you are in the right posture, it should almost feel effortless to maintain the position. A poor posture does the opposite — which can stress or pull muscles and cause pain. When you stand, your weight of your body should be evenly distributed across the balls of feet (not the heels or the front).

Take a minute out now and examine your current posture in front of a mirror (full-length if possible; otherwise get one that allows you to see at least the upper half of your body). Does it fit the description of a good posture? If not, take a look at the bad postures page on the right bar to fix your problem.

To read more, choose a topic on the categories bar on the right.

Stretch to relax hip flexors: Kneel on one knee and tighten your gluteal muscles (muscles in the buttocks) on the leg you are kneeling on. You will feel a stretch in the front part of your hip. Raise the arm on the same kneeling side and stretch towards the opposite direction. Hold this position for 30 seconds, relax, and repeat again 4 times.

Exercise to strengthen gluteal muscles: Lie down on your back and bend your knees to about 90-degrees. Squeeze your gluteal muscles together and push your hip upwards till your body forms a straight line from knees to shoulders. Hold this position for 5 seconds, relax, and repeat three times. Do this 10 times daily.

Most Importantly, remember to get up and move around once in a while when sitting and working on a computer.


Sources:
http://www.swolept.com/posts/fixing-anterior-pelvic-tilt-posture-tricks-to-make-your-butt-and-gut-smaller#.Ut5BAPawpGH

http://health.india.com/diseases-conditions/top-5-bad-postures-that-can-affect-your-health/

Exercises for fixing a hunchback:

Upper back foam rolling to increase the mobility of your upper back. Lie on a foam roller placed in the middle of your back and perpendicular to the spine. With your face facing upwards, keep your hands behind your head and bend your upper back over the roller five times.  You can repeat for each segment of your upper back by adjusting the roller.

Superman to strengthen the weak muscles on your back. First, lie with your face down, arms on the sides, and palms facing down. Slowly lift your chest and hands off the floor, stretching as far and as high as you can while pressing your shoulder blades together and keeping your chin down. Hold this position for eight seconds. Do this eight times. Repeat two to three sets daily.


Withhold a good posture.

When standing: keep your chest high, your shoulders back and relaxed. Try not to tilt your head forward, backward or sideways. Instead, tuck your chin down slightly and pull your head back and up as if your neck is against a wall. Make sure your knees are relaxed, not locked. Keep your feet parallel and your weight balanced evenly on both feet.

If you're standing for a long period of time: alternate between leaning on your left and right feet.

When sitting: have your back firmly against the chair. Your feet resting flat on the floor while keeping your knees level or a little lower with your hip. Keep your upper back and neck comfortably straight. Avoid leaning forward.


Sources:
http://www.pinterest.com/pin/16607092349809066/
http://www.barstarzz.com/howto/superman-lower-back-exercise/
http://health.india.com/diseases-conditions/top-5-bad-postures-that-can-affect-your-health/

Bad posture #1: Hunchback
Causes: Commonly caused by sitting hunched for long hours without stretching, for example in front of a computer screen.

Identification: Have someone take a photo of you standing sideways. If you notice that your upper back is excessively curved (greater than 40-45 degrees) as in the photo to the right, you have hunchback posture.

Problem: This poor sitting posture causes the chest muscles to tighten up, leading to an excessively curved back in the thoracic (upper back) region. The muscles of the upper back loosen and weaken. Causes  pain in the neck, shoulder, and back.

Bad posture #2: Anterior Pelvic Tilt
Cause: Long periods of sitting without stretching,  tightening the hip flexors (muscles which allow you to move your thighs up towards your abdomen).
Identification: Have someone take a photo of you standing sideways. If you look like the person on the left, you probably have anterior pelvic tilt.
Problem: Hip flexors tighten and glutes (muscles of the buttock) become weak. Another major problem is the way you would look, having your belly stuck out. May cause pain in the lower back.

Bad posture #3: Rounded Shoulder
Cause: Sitting in a bad position/posture while typing for a long time, or imbalanced exercise regime involving excessive chest pressing.
Identification – The “Pencil Test” is a method involving the patient to hold a pencil or pen in each of his hands. As shown in the photo above, if the pencils are pointing straight forward with your arms comfortably at his sides, this indicates a correct posture. If on the other hand the pencils are facing each other, or are rotated at an angle, then you have internally rotated shoulders (rounded shoulder).
Problem: Sitting in this kind of positions tightens the chest muscles, causing the shoulders to rotate forward internally. The muscles of the upper back weaken and loosen, resulting in possible pains on neck, shoulder and back.

Bad posture #4: Over-Pronated Feet
Cause: Pregnancy, obesity, inappropriate footwear can all weaken the arch, resulting in over-pronation of the foot and sometimes flat feet.
Identification – As shown in the photo above, put both hands 1 inch away from each side of your foot. Straighten your ankle so that the space between each hand and your ankle is equidistant. Now naturally let your ankle and feet rest. If your foot and ankle caves inward, you have over-pronated feet.
Problem: It adds pressure onto the foot, tightens the calf muscles, and may rotate the knees towards each other. Conditions such as Metatarsalgia (pain in the toes of the feet), heel spurs (growth of an extra bone from the heel), plantar fasciitis (pain in the sole of the foot), and bunions (a condition where the part where the great toe joins the rest of the foot, points outwards) are frequently resulted. Medial knee pain, hip pain, and low back pain are also brought with.

Bad posture #5: Forward Head
Cause – Sitting in an  chair hunched over while staring at a computer for extensive sessions.
Identification – Let someone take a photo of you standing sideways like what is shown in the photo on the left, locate the AC joint (pointed bony protrusion on the side of your shoulder) and check if your ear lobe is on top of the AC joint. If your ear lobe extends in front of your AC joint, you have a forward head posture.
Problem: Muscles in the back of the neck become tight, along with the upper back muscles of trapezius and levator scapulae. Creates pain in the neck.

Bad Posture #6: Forward Hip Tilt
Cause – Sitting too much and not stretching, which shortens the hip flexors.
Identification – It can be pretty hard trying to identify a forward tilt, one way of identifying is to purposely tilt your pelvis forward as far as you can, then backward as far as you can. You may realize your natural hip tilt is not far away from the exaggerated forward tilt, which is bad.
Problem – Forward hip tilt is associated with the tight hip flexors, which is a group of muscles in the front of your hips which pulls the knee upward. As you walk, tight hip flexors prevent the gluteus maximus(butt muscles) from activating, which forcing the hamstring muscles to become overworked and excessively tight. If you have tight hamstrings, the root cause may be tight hip flexors and an forward hip tilt.

Sources:

http://www.builtlean.com/2011/11/28/posture-problems/

http://health.india.com/diseases-conditions/top-5-bad-postures-that-can-affect-your-health/

http://www.swolept.com/posts/fixing-anterior-pelvic-tilt-posture-tricks-to-make-your-butt-and-gut-smaller#.Ut5BAPawpGH