Biomechanics - other principles
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Every body segment has what two things, as it relates to gravity?
- A center of gravity;
- Is acted on by the force of gravity
What is the line of gravity (LOG) and what direction does it apply force?
- Downward direction of the force of gravity on an object;
- applies force vertically, towards the center of the earth
What is the center of gravity (COG)?
- The point of exact center around which the body freely rotates;
- Point around which body weight is equal on all sides;
- Point of intersection of the three cardinal body planes
Where does the COG lie in the body?
Approximately anterior to the 2nd sacral vertebra when the body is in anatomic position
Does the body's COG change?
Yes, it changes as the segments of the body move away from the anatomic position
What is the based of support (BOS)?
Area of contact between the body and supporting surface
How is balance maintained?
When the COG remains over the BOS.
What is stability?
The firmness of balance, where the COG falls withing the BOS.
How do you attain increased stability?
When the COG is closer to the BOS.
How do you attain maximal stability?
When the COG is placed over the center of the BOS.
What is the rotation of a segment of the body dependant on?
- The magnituide of the force exerted by the effort force and the resistance force;
- The distance of these two forces from the axis of rotation
What does changing the torque do, in term of exercise?
Provides a method for altering the difficulty of an exercise when weight is applied.
What does applying weight to an extended arm do? What happens if you move the weight closer to the body?
- Changes the COG of the arm to more distal positions, requiring greater muscular support to maintain the arm in a horizontal position.
- Moving closer to the body, less muscular effort is required.
How do pulley systems in a gym work in terms of resistance?
They don't act in a vertical direction (like free weights), but exert effects that vary according to the angle of the application.
What is distractive force, and why is it used?
- Weights applied to the extremeties that exert traction;
- Used to promote normal joint movement in rehabilitation exercies, but they can also be injurous or undesirable.
What are the 4 types of motion?
When does translatory motion occur?
- When a freely moveable object moves in a straight line when a force is applied on the center of the object;
- When the object is free to move in a rectilinear or curvilinear path, regardless of where the force is applied
What does rotary motion occur?
- When a force is applied off center to a freely moveable object;
- When the object is free to move only in a rotary path, regardless of where the force is applied.
What is velocity?
The distance traveled in a period of time
What is acceleration, as it relates to velocity?
Refers to increasing velocity
What is deceleration, as it relates to velocity?
refers to decreasing velocity
What is momentum?
- The mathematical product of the mass and velocity of a moving object;
- M = mv
What is a lever and how are they used?
- A rigid bar that revolves around a fixed point or axis (fulcrum);
- Used with force to overcome resistance
What are the parts of a lever? Define those parts.
- Axis - pivot point between the force and resistance;
- Force Arm - distance from the axis to the point of application of force;
- Resistance Arm - distance from the axis to the resistance
What is a first-class lever, and example in the body?
- The axis between the force and the resistance arm and the force arm may be greater than, smaller than or equal to the resistance arm.
- Acting like a seesaw;
What is a second-class lever, and example in the body?
- The resistance lies between the effort force and axis of rotation, and the force arm is greater than the resistance arm.
- Acting like the wheel of a wheelbarrow;
- Plantarflexion pushing off ground
What is a thrid-class lever, and example in the body?
- The effort force lies closer to the axis of the lever than the resistance, and the force arm is smaller than the resistance arm;
- Every muscle of body serves as 3rd class-lever
How do levers apply to the body?
- Joint = axis (fulcrum)
- Contraction of skeletal muscles around the joint = force
- Moving segment = resistance
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