Balance and Posture Flashcards
Human vs Animal
Compared to (four legged) animals, humans are precariously balanced.
- Small contact area (base of support) of the feet relative to the rest of the body.
- High position of the center of gravity relative to the ground.
- Necessity of control mechanisms to keep balance.
Center of Gravity (CoG)
Point of application of the resultant of gravitational forces.
In anatomical position, it lies anterior between S1 and S2.
Changes with changing of body and limb position.
Center of Mass (CoM)
Theoretical point (measured/calculated) in relation to which the mass of this body is uniformly distributed. Does not change. CoM and CoG are at the same point in upright position.
Base of Support (BoS)
Refers to the area beneath an object or person that includes every point of contact (e.g. feet, hands, crutches, chair…) it makes with the supporting surface.
The bigger the BoS the better.
Limits of stability
Inverted pendulum rotating around the ankle joint with the intended equilibrium position being a slight forward tilt of the body.
Generates a gravity-driven instability.
What is the role of anti-gravity postural muscles?
To control balance.
Generate torque across joints to:
- Resist the tendency to be over-thrown
- Keep limbs, joints, body segments in proper relationship to one another so that the CoG falls within the BoS.
Erect Bipedal Stance
Body weight is borne exclusively by the two lower extremities.
Allows person to use upper extremities for performance of large and small motor tasks.
Disadvantages of Erect Bipedal Stance
In comparison with quadrupedal posture:
- Increase the work of the heart.
- Places increased stress on the vertebral column, pelvis and lower extremities.
- Reduces stability.
Posture
Stereotypical alignment of body/limb segments.
Good posture refers to a position that requires the least effort to maintain (least amount of muscle contractions), puts the least strain on ligaments, bones and joints.
Static Posture
Body and its segments are aligned and maintained in certain positions.
Sitting, standing or sleeping.
Not moving.
Coordination and interaction of various muscle groups which are working statically to counteract gravity and other forces.
Dynamic Posture
Postures in which the body or its segments are moving.
Walking, running, bending over.
Required to form an efficient basis for movement. Muscles and non-contractile structures have to work to adapt to changing circumstances.
Line of Gravity
Highly variable.
In ideal posture, gravity produces a torque to help maintain the optimal shape of each spinal curvature, allowing to stand easily.
Where does the gravity line fall in the sagittal plane?
- Forward of ankle
- Through or forward of the knee
- Through or behind the hip
- Through or behind the thoracic spine
- Through acromion
- Through or forward of atlanto-occipital
Where does the gravity line fall in the frontal plane?
- Symmetrically between two feet
- Through the umbilicus
- Through the xiphoid process
- Through the chin & nose
- Between the eyes
Anti-Gravity Muscles
- Neck muscles
- M. erector spinae
- Gluteus muscles
- Hamstrings
- Calf muscles, soleus
- Cervical muscles
- Abdominal and deep hip muscles
- Knee extensors, quadriceps femoris
What are the effects of bad posture?
- Misalignment of the musculoskeletal system.
- Increase in pressure on the spine, making it more prone to injury and degeneration.
- Neck, shoulder and back pain.
- Decrease in flexibility.
- Affects how well joints move.
- Affects balance and increases risk of fall.
- Harder to digest.
- Harder to breathe.
Lordosis - Body Segment Alignment
Pelvis anteriorly tilted.
Knees in hyperextension
Ankle joint slightly plantar flexed
Lordosis - Muscles Commonly Elongated and Weak
- Anterior abdominals
- Small muscles of lumbar spine (multifidus, rotators)
- Lower and middle trapezius
- Rhomboids
- Thoracic and cervical erector spinae
- Hyoid muscles
Lordosis - Muscles Commonly Short and Strong
- Lumbar erector spinae
- Hip flexors
- Upper trapezius
- Pectoralis major - minor
- Levator scapulae
- Sternocleidomastoid
- Scalenes
- Suboccipital muscles
Lordosis - Joints Commonly Affected
- Lumbar spine
- Pelvic joints
- Hip joints
- Thoracic spine
- Scapulothoracic joints
- Glenohumeral joints
- Cervical spine
- Atlanto-occipital joints
- Temporomandibular joints
Kyphosis - Body Segment Alignment
- Head held forward with cervical spine hyperextended.
- Scapula may be protracted
- Increased thoracic kyphosis
- Hips flexed, knees hyperextended
- Head is usually most anteriorly placed body segment
Kyphosis - Muscles Commonly Weak and Elongated
- Neck flexors
- Upper and thoracic erector spinae
- External obliques
- If scapula is protracted, middle and lower trapezius
- Rhomboids
Kyphosis - Muscles Commonly Short and Strong
- Neck extensors
- Hip flexors
- If scapula is protracted, serratus anterior, pectoralis major and/or minor, upper trapezius, levator scapulae
- Upper abdominal muscles
- Intercostales
Kyphosis - Joints Commonly Affected
- Thoracic spine
- Scapulothoracic joints
- Glenohumeral joints
Sway Back - Body Segment Alignment
- Long kyphosis with pelvis the most anterior body segment, hip joint moves forwards of posture line (thoracic spine mobile to compensate).
- Lower lumbar area flattens
- Pelvis neutral or in posterior tilt
- Hip and knee joint hyperextended
Sway Back - Muscles Commonly Elongated and Weak
- One joint hip flexors
- External obliques
- Lower thoracic extensors
- Lower abdominals
- Neck flexors
Sway Back - Muscles Commonly Short and Strong
- Hamstrings
- Hip extensors
- Upper fibers of internal obliques
- Internal intercostales
- Low back musculature short but not strong
Sway Back - Joints Commonly Affected
- Lumbar spine
- Thoracic spine
- Cervical spine
- Pelvic joints
- Hip joints
- Scapulothoracic joints
- Glenohumeral joints
- Atlanto-occipital joints
- Temporomandibular joints
Flat Back - Body Segment Alignment
- Loss of lordosis with pelvis in posterior tilt
- Hip and knee joints hyperextended
- Forward head posture with increased flexion to upper thoracic spine
Flat Back - Muscles Commonly Elongated and Weak
- One joint hip flexors
- Lumbar extensors
- Local stabilizers (multifidus, rotatores)
- Scapular protractors
- Anterior intercostales