Biomechanics and Force

The study of the forces and torques affecting movement and the description of the resulting movement

A push or pull that either produces or has the capacity to produce a change in motion of the body

The sum of multiple forces from multiple directions acting on the body, which determines the resulting change in motion.

• Law of Inertia
• Law of Acceleration
• Law of Reaction

A body will maintain it's state of rest or uniform motion in a straight line unless acted on by an external force

• 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.

a = f/m OR f = m*a

• f = force
• a = acceleration
• m = mass

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.

• reaction
• friction
• muscular

• 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

• Measured with a force plate in 3 directions:
• vertical
• anteroposterior
• mediolateral
• The net effect of the 3-D forces determines the resulting movement

• walking
• running (higher force in running)

Evaluating ground reaction force patterns

When two objects interact, friction acts paralell to the surface contact of the object in a direction opposite the motion or impending motion.

When walking friction force occurs paralell to the ground in the opposite direction that you're walking

Ff = mN

• Ff = frictional force
• m = coefficient of friction -- nature and interaction of the contacting surfaces
• N = normal force -- force pressing the surfaces together

• The pulling force on the bone that muscles provide;
• Must be present to move body segment;

Through the net effect of individual muscle forces acting across the joint

• 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

The rotary effect of force produced by a muscle or group of muscles

From the coordinated actions of the muscles acting across the joint

From disruptions in the coordinated muscular actions.

• Application of inappropriate force
• Co-contraction of musculature
• Muscular weakness
• Neurological disorders affecting muscular recruitment