Download chapter - American Kinesiology Association

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