People often adopt a simplistic view when assessing posture and alignment; for example, they measure only strength and flexibility and ignore the complexity of the factors involved. Strengthening a certain muscle group or stretching another to improve posture and alignment is not enough. Correcting alignment is a process of neuromuscular reeducation that requires enormous commitment, patience, and the guidance of a scrutinizing eye.
Posture may be observed in terms of the alignment of the joints and bony landmarks and understood in terms of muscle balance and function. It is often described relative to a plumb line—a straight line that runs vertically through the body. When viewing the body from the side in relation to the plumb line, deviations in an anterior–posterior direction become apparent (in the sagittal plane). The following landmarks of the body should line up vertically on the plumb line: the lobe of the ear, bodies of the cervical vertebrae, shoulder joint, midpoint of the trunk, greater trochanter of the femur, a point slightly anterior to the midline of the knee, and a point slightly anterior to the lateral malleolus (ankle).
Please note that ideal posture is the ideal, a goal that one strives for but may never achieve. Each individual is different in body type, center of gravity, habitual movement patterns, mental state, and genes; it is inconceivable to think that one posture will fit all. However, the concept of an ideal posture serves as a guideline and a reference by which we can detect deviations and gauge changes.
Posture affects every movement, exercise, and decision in an exercise program. Consider, for instance, a person who has fatigue posture, which is characterized by a rounded thoracic spine and the pelvis being forward of the plumb line in a posterior tilt. Although correction is complex, it generally involves extending the upper back, strengthening the upper back extensors, strengthening the iliopsoas, and stretching the external obliques of the abdomen. Bringing the shoulders into ideal alignment over the pelvis is also often helpful. On the other hand if a person has lumbar hyperlordosis, which involves an increased lumbar curve of the spine often accompanied by an anterior tilt of the pelvis, correction generally focuses on strengthening the abdominals and stretching the hip flexors and lower back extensors. Clearly these two people will receive different exercise programs, emphasizing different muscle groups, with the selection of exercises and the cueing appropriate for their particular posture.
This is an excerpt from Pilates.