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

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.

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.

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.

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.

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.

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.

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.

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.

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

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

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.

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.

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.

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

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.

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.

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

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.

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.

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.

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.

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.

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.

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

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.

Chapter 15: The Standing Posture