Bet you don't see too many people who work on their computers with such perfect posture.  These days it's tough to maintain if you don't put your mind to it.  

The 21st century lifestyle leads most of us to slump while watching television, working on the computer, or while we drive. You can notice the shoulders become rounded forward, the chin juts forward, the abdominals become weakened and we get a tight lower back.  Yuk!
Beyond that, the knees may not track under the hips and the feet may pronate or supinate. These issues can wreck havoc with our musculoskeletal system over time. This is especially true when we add in running or other impact activities.

What exactly does good posture mean? Well, it is the correct anatomical alignment of our musculoskeletal system.

Here is a checklist from the top of the head to tips of our toes.

1.  There should be a feeling of length from the crown of the head upwards
2.  Chin should be in
3.  Shoulders down and back
4.  Shoulders aligned over hips
5.  Back straight but in keeping with natural curves
6.  Belly pulled in but not so much that the chest (thoracic cavity) projects forward          
7.  Relaxed back
8.  Knees over feet

What are the muscles that should be kept strong for great posture:
1.  The muscles of the Core (all around trunk)
2. The back muscles especially the Rhomboids (upper back)
3. The Rear deltoids (back of shoulder)

Exercises for posture
1.  Abdominals with a towel:  These are amazing and easy to execute.  Just lie on your back with a towel under your head and your hands holding on the the sides of the towel.  Slowly raise your upper torso and lower.  I like three counts up and three counts down.  Head should rest on towel while doing the exercise.

2. Pilates:  Pilates mat classes are terrific for the back and wonderful for core strength.  If you can afford a private training session with a pilates teacher, it is an outstanding way to get connected to your body.

3.  Hamstring stretches: The hamstrings (back of legs) are important because if they become very tight the lower back can be compromised . I stretch them daily and anywhere.  Be gentle, of course, and never overdue.

4  Pectoral muscles should be stretched.(chest muscles) I like to put my arms on a doorway and allow my torso to go forward.  It gives a nice stretch.  The chest closes forward with all the computer work.

5:  Superman with alternating arms and legs:  This exercise is done on the belly while you lift and lower your arms and legs.  I love how it strengthens the back and gives a nice, subtle stretch to the front of the body.

6:  Shoulder work from a prone position (face down) . These work the rear deltoids and are simple to execute though not easy.  While lying on your belly, take your arms out to a T position.  Now bend them to form right angles.  Do your best to lift off the floor, hold for a count or two, and lower.

7:  Plank:  Many people love the plank for its core strengthening abilities.  It's a staple exercise.  Be sure to exhale sharply and pull the abdominals upward.

8:  The yoga exercise "Cat and Cow":  A wonderful stretch for the back and safe for most.  It is performed on the hands and knees and done slowly.

9:  Bridge work on floor:  Another position that will help tighten the glutes and stabilize the lower body.  I love it!  There are lots of variations and all are great.  Keeping the legs parallel and lifting the buttocks slowly up and down off the floor is the staple but there are lots of variations.
a. legs together or with a ball or pillow between the thighs for inner thigh strengthening.  
b. legs parallel  or try lifting 1 leg in the air at a time for more difficulty.
c. legs wide or place a resistance band around the legs for increased outer thigh resistance
 

If knees hurt in this position, try moving the feet a little further forward.

Gentle spinal twists are wonderful as well as simple foot exercises like ankle rotations.

If you are working hard at your desk, try taking mini-breaks to stretch the hamstrings, lower back and shoulders for mid-day rejuvenation.  This mini-break will go a long way in keeping your body happy.