Posture is the arrangement of body parts in a state of balance that protects the supporting structures of the body against injury or progressive deformity, which is a definition given in 1947 by the Posture Committee of the American Academy of Orthopedic Surgeons (Cailliet, R, 1983). By this definition, having and adopting a good posture is therefore effortless, non fatiguing, and painless even when you were to remain in erect position for long periods (Cailliet, R, 1981). Studies have shown that muscles function most efficiently when adopted in such an alignment, where the joints are optimally positioned (Bullock-Saxton, J, 1988).
To achieving an optimal posture, it combines both minimal muscle work and minimal joint loading and stress to the joints. The combination of these two factors is important, where in the event when optimal posture is lost (e.g., in slouched standing), although the muscle activity is clearly reduced, there is a significant increase in joint loading, which often will lead to joint pain and soreness.
Joint loading should be minimized over time where articular cartilage gains its nutrition through intermittent loading (Norris, C.M, 1998), and an even distribution of force is preferable as compared to point pressure. Contact pressure is directly proportional to the transmitted force but inversely proportional to area, since pressure is equal to force over area (McConnell, J, 1993). Distributing force over a larger surface area by optimizing segmental alignment, thus, reduces joint surface compression and lessens the risk of degenerative changes to a joint. The objective of any posture should be aiming towards reducing total energy expenditure and lessen stresses on the supporting body structures.
Tai Chi in particular focus and helps to prevent or eliminate injury and pain such as the knee pain, hip pain, shoulder pain, soreness and fatigue which is often due to poor postural habits and sedentary lifestyle. This is achieved by adopting the principle of Tai Chi optimal posture alignment (Figure 1) during both static and dynamic posture in the practice of the Tai Chi routines.
Any change in the alignment of one body segment automatically causes neighboring segments to move in an attempt to maintain stability (Newton’s 3rd law). Therefore, if one body segment moves forward, for instance, another must move backward to keep the body’s line of gravity (LOG) within the base of support for counterbalance. Eventually, this changes in force per unit area will cause tissue adaptation (Norkin. CC and Levangie. P.K, 1992). Changes in serial sarcomere number within muscles, for instance, are adaptations to postural changes over time. The shortening of ligaments leads to reduced range of motion, whereas lengthening ligaments reduce a joint’s passive stability.
Tai Chi apply the same principle of Newton’s 3rd law of equal and opposite reaction during the movement transition to maintain the line of gravity and to obtain maximal stability with minimal joint loading. The extension of the leg is often counterbalance by the extension of the arms in the opposite direction while maintaining the optimal posture alignment.
Static posture is when the body remains stationary and reflects the alignment of the body segments. This is affected by both changes in load distribution across joints and resting muscle length. Such postures include standing, sitting and lying. Dynamic posture is the body position during movement transition and it gives information about body segment alignment, muscle actions, and motor skill. Typical dynamic postures are walking, running, jumping and lifting. You can use descriptions of both position (kinematic) and force (kinetic) to assess posture.
Excessive changes in posture from the optimal position due to poor postural habits during standing, sitting and walking can give rise to asymmetrical tissue tension. Ultimately, tissue failure can result from repeated passive tissue strain. Avoidance of end-range postures that load the soft tissues excessively may reduce short-term pain as well as long-term pain cause by overuse. The cause of many muscle imbalance such as the shoulder (one side higher than the other), back (scapular protruding on one side), lower back (pelvic higher on one side) are often due to poor postural habit which developed over time.
Scannell and McGill (Scannell. J.P and McGill. S.M, 2003) studies subjects who had either increased lordosis (hyperlordosis) or reduced lordosis (hypolordosis). The investigation modified subjects’ posture using 12-week exercise program and demonstrated a change in posture toward a midrange (neutral) lordosis (Christopher M. Norris, 2008).
One of the benefits of Tai Chi exercise program is its ability to help correct poor postural habits and improve overall range of motion when practiced correctly. The combination of the mind and body in Tai Chi helps practitioners to visualize and be mindful of the line of gravity during any movement transition in Tai Chi, thus enabling the practitioners to adopt and habitualise the good posture habit which can be positively transferred to daily activities, since many of the Tai Chi movements are functional movements.
Through continual Tai Chi practice, the overall kinesthetic awareness of the body improves over time where the body becomes more sensitive to the misalignment of any posture and will move in a position to correct this misalignment. This however could not be achieved without proper Tai Chi exercise program.