CHAPTER IV
BODY MECHANICS
Body Mechanics
• Definition: the use of one’s body to produce
motion that is:
-safe,
-energy conserving,
-and efficient,
all of which allows the person to maintain
balance and control
Why Learn about Proper Body
Mechanics?
• Ensures clinician and patient safety
• Places less stress and
strain on the body,
preventing injury
• To conserve energy
Benefits of proper
Body Mechanics
 Conserve energy
 Reduce stress and strain to muscles, joints, ligaments, and soft
tissue
 Promote effective, efficient respiratory and cardiopulmonary
function
 Promote and maintain proper body control and balance
 Promote effective, efficient, and SAFE movements
Terminology
• Gravity:
The force that pulls all objects toward the
center of the earth.
• Friction:
The act of rubbing one object against
another.
Center of gravity (COG):
• The point at which the mass of a body or
object is centered; when weight on all sides is
equal
• Base of Support (BOS):
Area on which an object rests and that
provides support for the object
• Line of Gravity:
The vertical line between the center of gravity
and the ground
Must fall within the BOS if the “body” is to
stay upright
May be shifted
Proper Body Mechanics
• Gravity & Friction are forces that add resistance
to many activities
- lifting, reaching, pushing, pulling, and carrying
an object.
• Select and use techniques that:
- reduce the adverse effects of gravity or
friction
- and/or enhance the positive effects of these
TWO forces.
Principles of Body Mechanics
• Remain close to the object
• Use short lever arms for
better control & efficiency
(with less strain)
•
The synchronized use of as many large muscle groups as
possible during activity increases overall strength and
prevents muscle fatigue and injury
– To move objects below your center of
gravity, begin with the hip and knees
flexed
– Use gluteal and leg muscles rather
than the sacrospinal muscles of the
back to exert an upward thrust
when lifting weight
– Face the direction of the movement
to prevent twisting of the spine
Maintain your COG close to the object’s COG
• Widen your BOS and position your feet
according to the direction of movement you
will use to perform the activity
• Avoid twisting your body when you lift
• When possible, push, pull, roll, or slide an
object rather than lifting it
•
The greater the friction against a surface beneath an object,
the greater force required to move an object. Provide a firm
smooth, dry foundation before moving the object.
Causes of Back Injuries
• Repetitive Motion/twisting
• Forward bending
• Poor or improper lifting techniques
• A loss of flexibility
• Poor posture
• Poor Job design
• Deconditioned/Poor physical fitness
• Overweight/Smoking
• Nutrition/Stress
Mechanics: Twisting
• Repetitive twisting can do damage to the
spine.
• It over stretches ligaments and muscles
causing weakness.
• Can damage discs especially combined with
bending.
Mechanics: Forward Bending
• Forward bending can over-stretch the low back
muscles to the point where they can lose strength
to protect the spine from injury.
• The ligaments are also weakened
• Can increase stress on the discs
• Range of the bend and time spent in the position
can determine amount of damage
Mechanics: Poor Posture
• It is one of the main reasons that injuries occur
• Means that the spine’s normal curves are
exaggerated or decreased creating stresses and
strains in the tissues.
• The result is pain and dysfunction and can lead to
serious injury.
Mechanics:
Poor Job Design/ Ergonomics
Injury can occur when:
•
Moving a load too heavy
•
Moving a load too often
•
Moving a load too far
•
Twisting with a load
•
Vibration
•
Improper chair/equipment
Poor ergonomics
Mechanics:
Poor Physical Fitness
• Decreased oxygen delivery to muscles can
cause muscles to wear down and lead to
weakness.
• This is one of the main cause for injury
Mechanics:
Overweight & Smoking
• Obesity causes extra work for the spinal
muscles to maintain the curvature.
• Leads to excess fatigue and wear/tear in the
body
• Nicotine damages connective tissue
decreasing circulation and oxygen in the blood
which affects muscle strength
Mechanics: Nutrition & Stress
• Malnutrition can lead to injury. Because
- Muscles need protein to repair worn
musculoskeletal tissue
- Bones need minerals for strength
• Stress stiffens and weakens back muscles and
increases pain sensitivity
PROPER LIFTING TECHNIQUES
• Stand with feet apart one foot slightly ahead of
the other. Wide stance helps balance during
lifting
• Squat down keeping back straight, keep chin
tucked, and lift smoothly
• Keep object close to you
• Bend your knees and hips using legs to lift
Proper Lifting Techniques
• Maintain lumbar curve
• Face the object you are picking up
• Push rather than pull (Pushing is easier)
• Stabilize hands on the object
• Take your time-hurrying causes muscles to act
inappropriately and increases chance of injury
Lifting (Don’ts)
When lifting objects, DO NOT:
• Lift in a bent-over, stooped position
• Twist at waist
• Lift with one hand
• Lift with outstretched arms
• Keep feet together
• Lift above shoulders or below knees
Avoid being STATIC
• Change stressful positions often
• If you are sitting for too long- stand
• If you are standing for too long- stop and squat
• If you are working in computer give a break every 30
minutes.
Sitting and
Computer station work
• Sit close to your work
• Hips, knees and ankles are open to 90 degrees
• Elbows are open to 90-120 degrees
• Wrists are in relaxed and neutral position (not bent)
• Both feet are flat on the floor or use a foot rest
• Shoulders are low and relaxed
• Head and neck are aligned with spine
Sitting and
Computer work station
• Do not slump or lean forward or downward to reach
for work.
• Do not sit for more than 60 minutes without getting
up or changing position.
• Raise the height of the computer screen so screen is
at or slightly below eye level.
Proper ergonomics
Standing
• Bring your work close to you.
• Put one foot up, shift your weight and position
frequently.
• Keep your work at a comfortable height.
• Wear comfortable shoes
Standing (Don’ts)
DO NOT:
• Stand in one place too long.
• Stand bent forward at your waist or neck.
• Lock your knees into a straight or overextended position.
Pushing
• Push whenever possible.
• Keep head up, knees bent, and back straight.
• Keep the load in front and use both hands.
• Remain close to the item being pushed.
Reaching
When reaching for an object, remember to:
• Keep back straight
• Reach with two hands
• Face the object
• Stand on a stable step-stool to reach high items
• Bend knees slightly.
Reaching (Don’ts)
When reaching for an object, DO NOT:
• Overreach by standing on toes
• Reach with one hand
• Twist at waist
• Stand on an unsafe surface
• Reach with legs locked in straight position.