Biomechanics and Force
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What is biomechanics?
The study of the forces and torques affecting movement and the description of the resulting movement
What is force?
A push or pull that either produces or has the capacity to produce a change in motion of the body
What is net force?
The sum of multiple forces from multiple directions acting on the body, which determines the resulting change in motion.
Newton's 3 laws
- Law of Inertia
- Law of Acceleration
- Law of Reaction
What is the law of inertia?
A body will maintain it's state of rest or uniform motion in a straight line unless acted on by an external force
What is the law of acceleration?
- Acceleration of a body resulting from an applied force will be:
- Proportional to the magnitude of the applied force,
- In the direction of the applied force,
- inversely proportional to the mass of the body.
What is the formula for acceleration?
a = f/m OR f = m*a
- f = force
- a = acceleration
- m = mass
What is the law of reaction?
When two bodies interact, the force exerted by the first body on the second is met by an equal and opposite force exerted by the second body on the first.
For every action, there is an equal and opposite reaction.
Classifications of forces affecting movements
What is Ground Reaction Force (GRF)?
- Corresponds to Newton's law of reaction;
- As a body applies a force to the ground, the ground applies and equal and opposite force to the body
How is GRF measured?
- Measured with a force plate in 3 directions:
- The net effect of the 3-D forces determines the resulting movement
GRF occurs in what activities?
- running (higher force in running)
How do you asses for abnormalities in gait?
Evaluating ground reaction force patterns
What is frictional force?
When two objects interact, friction acts paralell to the surface contact of the object in a direction opposite the motion or impending motion.
An example of frictional force
When walking friction force occurs paralell to the ground in the opposite direction that you're walking
Formula for Frictional Force
Ff = mN
- Ff = frictional force
- m = coefficient of friction -- nature and interaction of the contacting surfaces
- N = normal force -- force pressing the surfaces together
What is muscle force?
- The pulling force on the bone that muscles provide;
- Must be present to move body segment;
How do joints move?
Through the net effect of individual muscle forces acting across the joint
What influences movement, as it relates to muscle forces?
- The net muscular force and the distance the force acts from the rotational axis of the joint;
- The length of the muscle at the time of contraction;
- the velocity of muscles shortening
What is torque?
The rotary effect of force produced by a muscle or group of muscles
How do normal joint movement patterns occur?
From the coordinated actions of the muscles acting across the joint
How do abnormal joint movement patterns occur?
From disruptions in the coordinated muscular actions.
Reasons abnormal joint movement occurs?
- Application of inappropriate force
- Co-contraction of musculature
- Muscular weakness
- Neurological disorders affecting muscular recruitment
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