Quiz 3.5 Flashcards
Balance
Keeping your body upright and stable
Dynamic OR static
Static Balance
Maintaining upright posture while being ‘still’
Ex: Standing
Dynamic balance
Maintaining upright posture while moving
Ex: walking
What does balance do for us
Allows us to maintain upright alignment, efficient movement patterns, load joints symmetrically
“good posture”
Least amount of energy expended
Center of mass
Point around which the mass is considered to be concentrated, represents total mass
Can reference whole body or segments
Location determines response to external forces
Center of gravity
Vertical projection of the COM on the ground
Center of Pressure
Point representative of the location of the average vertical ground reaction force vector (where COG is on ground)
Location depends on muscular contributions and # of points of contact
Moves A/P and M/L
Are A/P and M/L sway independent
No, they come in combo
Evert/invertors are also plantar/dorsiflexors (both planes)
Narrow foot means hip ab/add must assist to avoid loss of balance
Inverted pendulum
Axis as feet, body as pendulum
This is how standing is characterized because of the sway
Strategy to maintain upright posture
Vision providing us with reference points
Base of Support
Comprised of the outermost edge of points of contact with the ground
Key to balance
Keep your Com/COG within your base of support
Perturbation
Application of external torque
Strategies to maintain balance
Ankle, hip, stepping, suspensory
Automatic and happen 85-90 msec after instability is recognized
Ankle strategy
Slow, low amplitude perturbation
Contact surface is wide and longer than foot
Muscles recruited distal –> proximal
Head in-phase with hips
SEE graph of muscles
Hip Strategy
Fast, large amplitude perturbation
Surface is unstable or shorter than feet
Muscle recruited proximal–>distal
Head out-of-phase with hips (opp. direction)
SEE graph of muscles
Stepping strategy
Used to prevent fall (magnitude of force too large or fast and/or other strategies fail)
BOS moves to catch up with COM
Suspensory Strategy
Associated with large magnitude force
Forward bend of trunk (knee/hip flexion) progress into squat
COG lowered
Lower Cog means less ramifications if fall
Factors that influence stability
BOS
Vertical displacement of COM (COG)
Location of COG relative to BOS
When do we have greatest stability
COG close to the midline of BOS
Think athletic position
What muscles control A/P sway
Flexor and extensor muscles
What muscles control M/L sway
At ankle: invert/evertors
At hip: Ab/Adductors
Feed forward
The feedback that muscles use for stability
Activation after perturbation is applied is too late
Why is athletic stance popular (triple threat)
Increase BOS
Lower COM
Increase stability and places lower extremity joints flexed in active positions
How do we help people who can’t use athletic position
Canes, crutches, walkers
These change the BOS and add contact point
What is the key to life
Balance
