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Posture is the attitude assumed by body either when the body is stationary or when it is moving. Posture is attained as a result of coordinated action of various muscles working to maintain stability. ^[1]. Posture in easy terms can be understood as the position in which you hold your body when standing or sitting.

Types of Postures^[2]

The posture are basically divided in to two types:

1. Static 
2. Dynamic

Inactive postures– These are postures or attitudes adopted for resting or sleeping. They require theoretically minimal muscle activity, and are usually assumed in need of relaxation.

Active posture – The integrated action of many muscles is required to maintain active postures, they are basically divided in two types

1. Static postures- Body segments are aligned and maintained in a fixed positions. This is usually achieved by co-ordination and interaction of various muscle groups which are working statically to counteract gravity and other forces. Examples of static postures are standing, sitting, lying, and kneeling.
2. Dynamic postures- In this type of posture body segments are moving. it is usually required to form an efficient basis for movement.Muscles and non-contractile structures have to work to adapt for changing circumstances. Examples are walking, running, jumping, throwing, and lifting. 

Ideal posture^[3]

As is true for any testing, there must be a standard, same holds true for assessing postural alignment. The ideal skeletal alignment is  known as Ideal posture or Standard posture. To get an understanding of ideal posture, we need to know the ideal alignment of spine and other joints at rest. This is usually done by observation or using a plumb line, the line of gravity should pass through specific points of body if it is to be called ideal posture. On examination the body should be viewed from four aspects; anteriorly, posteriorly, and sides(left and right). The ideal “normal” erect posture is one in which the line of gravity (the vertical line drawn through the body’s Centre of gravity) when viewed from each side runs^[4]:

• Line of gravity passes through the external auditory meatus
• Then through the shoulder joint
• Approximately midway from trunk, going through the bodies of cervical and lumbar vertebras
• At hip joint joint it passes through the hip joint, approximately through greater trochanter of femur
• Anterior to the knee joint
• Anterior to lateral malleolus

When viewed from either the front or the back, the vertical line passing through the body’s centre of gravity should theoretically bisect the body into two equal halves, with the body weight distributed evenly between the two feet.

Muscle action in posture

The balanced posture of the body reduces the work done by the muscles in maintaining it in an erect posture. It has been determined (using electromyography) that, in general:

• The intrinsic muscles of the feet are quiescent, because of the support provided by the ligaments.
• Soleus is constantly active because gravity tends to pull the body forward over the feet. Gastrocnemius and the deep posterior tibial muscles are less frequently active.
• Tibialis anterior is quiescent (unless high heels are being worn).
• Quadriceps and the Hamstrings are generally quiescent.
• Iliopsoas is constantly active.
• Gluteus maximus is quiescent.
• Gluteus medius and tensor fascia latae are active to counteract lateral postural sway.
• Erector spinae is active, counteracting gravity’s pull forwards.
• The abdominal muscles remain quiescent, although the lower fibres of the Internal obliques are active in order to protect the inguinal canal.

Examples of different faulty postures

Some of the examples of faulty posture can be as follows

• Lordotic posture
• Sway back posture
• Flat back posture
• Round back (increased kyphosis) with forward head
• Flat upper back and neck posture
• Scoliosis(postural)

Resources

1. ↑ Gardiner MD. The principles of exercise therapy. Bell; 1957.
2. ↑ Gardiner MD. The principles of exercise therapy. Bell; 1957.fckLRLevangie PK, Norkin CC. Joint structure and function: a comprehensive analysis. FA Davis; 2011 Mar 9.
3. ↑ Kendall HO, Kendall FP, Wadsworth GE. Muscles, Testing and Function. American Journal of Physical Medicine & Rehabilitation. 1973 Feb 1;52(1):43.
4. ↑ Kisner C, Colby LA. Therapeutic exercise: foundations and techniques. Fa Davis; 2012 Oct 8.