chapter

11

Posture and Body Mechanics

Posture

• = Relative alignment of body segments with one another

• Good alignment: provides minimal stress to segments

• Poor alignment: creates imbalances stress adaptations efficiency

• Static posture used as the defining reference in evaluations

Standing: Anterior View

• Plumb line bisects the body into symmetrical segments.

• Line bisects nose, mouth, sternum, umbilicus, and pubic bones.

• Feet are equidistant from plumb line.• Palms face lateral thigh.

(continued)

Standing: Anterior View (continued)

• Level right to left: earlobes, shoulders, fingertips, nipples, iliac crests, patellae, medial malleoli

• Patellae: directed forward• Feet: directed forward or out slightly• Knees and ankles: in line with each other• Knees: straight• Symmetrical muscle development

Figure 11.1

Standing: Posterior View

• Plumb line bisects head and runs over spinous processes

• Level left to right: earlobes, shoulders, scapulae, hips, posterior superior iliac spine, gluteal fold, posterior knee creases, medial malleoli

• Scapulae lie against rib cage: T2-T7• Calcaneus: straight with Achilles perpendicular to

floor• Symmetrical muscles • Weight equally distributed

Figure 11.2

Standing: Lateral View

• Plumb line is slightly forward of lateral malleolus.

• Line passes through external auditory meatus, earlobe, bodies of cervical spine, center of shoulder joint, and greater trochanter.

• Line passes midway between back and chest, back and abdomen.

• Line runs slightly posterior to hip joint, slightly anterior to knee joint (behind patella).

(continued)

Standing: Lateral View (continued)

• Horizontal line between ASIS (anterior superior iliac spine) and PSIS (posterior superior iliac spine)

• Weight balanced between heel and toes• Knees straight but not locked• Chin slightly tucked• Chest up and forward• Mild curve inward at cervical and lumbar spine

Figure 11.3

Sitting Posture

• Seat height: allows feet flat on floor—90° at hips, 90° at knees

• Seat depth: front edge 1 to 2 in. from posterior knee

• Back height: to lower scapulae and support lumbar spine, thoracic spine

• Arms: allow shoulder relaxation and permit forearms to rest with elbows 90°

Figure 11.4

Sitting Posture at Desk

• Chair height: allows forearms to rest on desk with relaxed shoulders

• At keyboard: elbows at 90° or slightly more, wrists in neutral, fingers able to rest on keyboard

• NOT: forward head, rounded shoulders, flat lumbar spine, excessively curved thoracic spine, hyperextended wrists

Effects of Bad Posture

• Slow changes over time: adaptation to stresses applied

• Shortening of some structures, lengthening of opposing structures

• Secondary weakness of both shortened and lengthened structures (length–tension relationship)

Length–Tension Relationship

As a muscle either shortens from or lengthens beyond optimal length, strength decreases.

Results

• Efficiency of movement is impaired.• Stress on specific segments during sport

activities increases.• Muscles must work harder to maintain posture,

increasing fatigue.• Individual becomes susceptible to injury.• Injury may become exaggerated with increased

stresses already in place.

Pathological Alignments

• Pelvis• Spine segments• Lower extremity• Upper extremity

Figure 11.5

Figure 11.6

Figure 11.7

Figure 11.8

Figure 11.9

Figure 11.10

Figure 11.11

Figure 11.12a

Figure 11.12b

Figure 11.12c

Figure 11.13

Figure 11.14a

Figure 11.14b

Figure 11.14c

Figure 11.15

Figure 11.16

Figure 11.17

Figure 11.18

Figure 11.19a

Figure 11.19b

Figure 11.20

Figure 11.21

Figure 11.22a

Figure 11.22b

Figure 11.22c

Figure 11.23

Other Considerations Regarding Malalignment

• Sports increase postural deviations.– Anterior muscles are exercised more than

posterior muscles– Unilateral activities

• Age increases deviations.• Joint hyper- or hypo-mobility muscle

stresses.• Scar tissue from injuries can cause

imbalances.• Site of pain may not be site of problem.

Body Mechanics

• = The way the body is positioned and used during activity.

• Correct mechanics makes the most effective use of the body’s forces and levers.

• Incorrect mechanics leads to inefficient use and increases stress on the body segments.

Basic Principles

• Spine should remain straight.• Pelvis remains in neutral.• Lowering center of gravity increases stability.• Broadening base of support increases stability.• Feet are placed in direction of force application

or acceptance.• Trunk strength is vital for force transmission,

transfer, and body support.

Figure 11.25

Figure 11.26a

Figure 11.26b

Figure 11.26c

Figure 11.27

Figure 11.28

Figure 11.29

Figure 11.32