Chapter 8 - Stability & Instability

Ability to resist being disturbed or losing balance.

Stability

Ability to control the body over its base of support.

Balance

What does more stability mean?

More resistance to forces

What does less stability mean?

Less resistance to forces

What is stability related to mechanically?

Resistance to disturbance (forces acting on body)

What happens when athletes have poor stability?

Decreased preformance

Signs of poor stability include:

Poor body position, feet placed incorrectly, cannot regain balance, cannot move quickly, inefficient movement

What are the two types of stability?

Linear and Rotarty

Resistance to being moved in a straight line

Linear Stability

When is linear stability important?

When moving in a specific direction

Examples of high linear stability

Rowing team, Sumo wrestler

What does linear stability include?

Resistance to being moved AND resistance to being stopped/changed

Resistance to being rotated, tipped, or spun

Rotary Stability

What does strong rotary stability allow?

Resist torque (turning forces)

Who needs strong rotary stability?

Gymnasts, Judo athletes, Cyclists

Can you be balanced but not stable?

Yes; Example: one-handed handstand

What happens when COG leaves base of support (BOS)?

Gravity creates torque which leads to you falling

What increases torque from gravity?

Greater distance between line of gravity (LOG) and axis

Area under and between points of contact

Base of Support (BOS)

Vertical line from COG to ground

Line of Gravity (LOG)

When are you stable?

When LOG is inside BOS

Why do athletes sometimes become unstable on purpose?

To generate movement or apply force

Give an example of when athletes become unstable on purpose.

Wrestlers leaning forward to throw opponent

After the athlete becomes unstable, what must they do?

Quickly regain stability

List the main ways to increase stability.

Increase BOS, Lower COG, Increase body mass, Keep LOG in BOS, Shift LOG toward force

Which is more stable: one foot or two?

Two feet

Which is more stable: feet close or apart?

Apart

What happens when BOS increases?

Stability increases

Where must LOG be for stability?

Inside BOS

What happens as LOG gets closer to edge?

Stability decreases

What happens if LOG goes outside BOS?

Loss of Balance

Why do sprinters shift LOG forward?

Faster start

Are they stable in this position?

No (intentionally unstable)

What happens when COG is lower?

Stability increases

Why is crouching more stable?

COG stays within BOS

Standing tall vs crouching; what's more stable?

Crouching

How does body mass affect stability? Why?

More mass = more stability; Requires more force to move

What's harder for heavier athletes?

Regaining balance once lost

Why do athletes widen BOS toward force? Give an example.

Resist being pushed; Running back widens stance toward tackler

If force comes from front? If force comes from side?

Widen BOS front/back; Widen BOS side-to-side

Why do athletes lean into force? Give examples.

Maintain balance; Wrestlers lean into opponents, Batters lean into pitch

What are athletes doing when they lean?

Temporarily destabilizing themselves

Point where object balances without rotating. How do you find it?

Center of Gravity (Physically); Balance object on a point (apex)

What increases stability the MOST overall?

Large BOS + low COG + high mass

What decreases stability?

Small BOS, High COG, LOG near edge

What happens when distance between LOG and axis increases?

Torque increases, which creates instability

______ stability = Straight-line resistance

Linear

______ stability = Resistance to rotation

Rotary

When do athletes want minimal stability?

When they need to move quickly

How do they decrease stability?

Small BOS, Shift LOG