Chapter 15: The Standing Posture

1. Chapter 15:The Standing Posture KINESIOLOGY Scientific Basis of Human Motion, 11th edition Hamilton, Weimar & Luttgens Presentation Created by TK Koesterer, Ph.D., ATC Humboldt State University Revised by Hamilton & Weimar

2. Objectives • Identify and describe the skeletomuscular and neuromuscular antigravity mechanisms involved in the volitional standing position. • Summarize the similarities and differences that occur in the relation of the line of gravity to various body landmarks with good and poor anteroposterior segmental alignment. • Discuss the factors that affect the stability and energy cost for the erect posture.

3. Objectives • Explain the effects that the variables of age, body build, strength, and flexibility have on the alignment of body segments in the standing posture. • Name the values, if any, of good posture. • Perform kinesiological analyses on the posture of individuals of different ages and body builds.

4. SIGNIFICANCE OF POSTURE • Posture means position. • The multisegmented human body does not have a single posture. • Most posture research has been related to the volitional standing position. • All posture is somewhat dynamic, including postural sway during quiet standing. • Represents a person’s habitual carriage.

5. SUPPORT OF THE STANDING POSTURE Muscular Activity in Erect Standing • Humans have a very economical antigravity mechanism. • Muscle energy required to maintain erect posture is relatively small. • Ligaments play a major role in supporting and maintaining the integrity of the joints. • Muscles that are active are those that aid in keeping the weight-bearing column in relative alignment and oppose gravity.

6. Muscular Activity in Erect Standing Foot: Only muscular activity is in the push-off phase or rising on the toes. Leg: Posterior calf muscles are more active then the anterior. Thigh & Hip: Very little activity: • Swaying produces bursts of ab/adductors. • Iliopsoas constantly active, preventing hyperextension of the hip joint.

7. Muscular Activity in Erect Standing Spine: Very slight activity in sacrospinalis or abdominals. Upper Extremity: low-grade activity in a number of muscles: • Serratus anterior & trapezius support the shoulder girdle. • Supraspinatus resist downward dislocation of the humerus. • No activity in elbow or wrist joints when passively hanging.

8. The Neuromuscular Mechanism for Maintaining Erect Posture • Proprioceptors are responsible for most of the reflex movements to maintain posture. • Posture modification depends on: • Voluntary decision towards change. • Experience with desired posture. • Instruction resulting in different strategies. • Environmental influences.

9. Postural Stability • Hellebrandt (1940) “Standing is, in reality, movement upon a stationary base”. • CoG does not remain motionless. • Subjects were constantly swaying. • Today, computerized dynamic posturography can record postural sway magnitude, direction, and pattern. • Postural stability is currently measured as sway motion between CoG and center of pressure as well as CoG velocity.

10. Alignment of Body Segments • “Good posture” • Weight-bearing segments balanced vertically. • Rotary effect of gravitational force is minimized. Fig 15.2

11. Alignment of Body Segments • “Fatigue posture” • Muscles have let go. • Ligaments prevent collapse. • Zigzag alignment of weight bearing segments increases rotary effect of gravitational force. Fig 15.1

12. Alignment of Body Segments • Even the most ideal posture has some rotary force present. • Supporting column of trunk situated more posteriorly. • Support base (feet) project forward. • Spinal column curved anteroposteriorly. • Chest forms an anterior load. • Females breasts are an additional anterior load.

13. Relationship of Alignment of Body Segments and Integrity of Joint Structure • Prolonged postural strain is injurious: • Ligaments can permanently stretch. • Cartilages can be damaged due to abnormal friction. • Arthritic changes in weight-bearing joints.

14. Minimum Energy Expenditure • Cannot be accepted as the criteria of good posture. • Metabolic economy is desirable to a point. • Well-balanced segmental alignment should not be sacrificed for it. • A single interpretation of an ideal posture is neither practical nor possible.

15. FACTORS RELATED TO THE STANDING POSTURE Energy Cost • “Fatigue posture” . • Requires a minimum of metabolic increase. • Knees - hyperextended • Hips – forward • Increased thoracic curve. • Head – forward • Trunk - posterior lean Fig 15.3

16. Age • Infant lacks muscular strength to stand upright. • Posture in toddler more erect and less stable than in older child or adult. • Postural sway becomes more variable with aging. • Stability more dependent on vision, less on proprioception in aging population. • Level of muscle activity increases as stability decreases. • Increased tendency to fall with advanced age.

17. Evolutionary and Hereditary Influences • As man began to walk upright there was a shift from a vertically suspended position to a vertically supported one. • Although no specific principle is derived, changes had to occur to the musculoskeletal structure.

18. Strength and Flexibility • Seem to be universally accepted factors based on the preponderance of strength and flexibility exercises: • Strength of abdominals • Scapula retractors • Pectoral stretching • Hamstring stretching

19. PRINCIPLES APPLIED TO POSTURE • Weight-bearing segments aligned so trunk and pelvic girdle inclination is within “normal” limits. • Line of gravity intersects center of base of support. • Weight-bearing joints should be in extension, balanced, no strain or tension. • Good posture requires minimal energy expenditure for the maintenance of good alignment.

20. PRINCIPLES APPLIED TO POSTURE • Permits mechanically efficient function of the joints. • Good posture, both static and dynamic, requires a minimum of muscle force. • Good posture, both static and dynamic, requires sufficient flexibility in the structure of the weight-bearing joints to permit good alignment without interference or strain. • Good posture requires good coordination. • neuromuscular control & reflexes.

21. PRINCIPLES APPLIED TO POSTURE • Adjustments in posture can be made more readily with a good kinesthetic awareness of posture. • Good posture, both static and dynamic, is favorable, or at least not detrimental, to organic function. • The characteristics of normal posture change with age. • Posture of any individual should be judged on the basis of how well it meets the demands made upon it throughout a lifetime.

22. POSTURAL ADAPTATIONS TO EXTERNAL CONDITIONS AND SPECIAL PROBLEMS • Standing on an inclined plane: adjustments should be made at the ankle when possible; adjust CoG above the base of support. • Same for wearing high heels, pregnancy, and carrying a heavy bundle in front of the body. • Standing on a moving surface: be prepared to make adjustments to acceleration, deceleration, and side-to-side sway. • Comfortably wide stance in the direction of motion.

23. POSTURAL ADAPTATIONS TO EXTERNAL CONDITIONS AND SPECIAL PROBLEMS • Strategies for postural adaptation: • Hip strategy: • Adjustments to maintain center of gravity over base are made through hip and trunk flexion/extension. • Ankle strategy: • Adjustments to maintain center of gravity over base are made through changes in ankle/foot motion or position.

24. POSTURAL ADAPTATIONS TO EXTERNAL CONDITIONS AND SPECIAL PROBLEMS Standing on one foot: • Usually managed automatically by the muscle, joint, and labyrinthine proprioceptors, and reflex response. • Shift body weight to supporting limb.

25. POSTURE SCREENING • In an optimal standing posture the line of gravity falls: • slightly anterior to lateral malleolus • Midline of the knee • Slightly posterior to hip • Anterior to sacroiliac joints Fig 15.3a

26. POSTURE SCREENING • Subject should wear minimal clothing. • Subject assumes comfortable stance. • Landmarks to line of gravity from the side. • Alignment of foot, ankle, & knee from front. • Alignment of spine & pelvis from rear. A screening matrix expedites observation of any deviations.

27. Chapter 15:The Standing Posture