Biomechanics Angular Kinetics

Where does the line of application move?

through and past the point of application

What is centric force?

a force that moves straight through the object’s center of mass

What is eccentric force?

a force that moves through one side of an object and causes torque

What is torque?

an angular force

What is a moment arm?

the perpendicular distance from the line of action to the pivot point

How can you change the moment arm?

by changing the angle of the line of action

What 3 forces generate torques on the human body?

muscle forces, gravitational forces, and external forces

How can you alter torque?

by changing the length of moment arm or the force on the line of action

What is needed to maintain torque for an exercise like a bicep curl?

increase in muscle force during flexion and extension

What is a force couple?

a pair of equal forces acting on opposite sides of the axis of rotation

What are levers?

a rigid rod that is rotated about a fixed point known as a fulcrum

What is mechanical advantage calculated for?

to evaluate effectiveness of a lever

What does a larger mechanical advantage mean?

the object is easier to move

What does a smaller mechanical advantage mean?

a greater effort force is required to overcome resistance force

What does it mean when mechanical advantage is = 1?

that effort arm = resistance arm

What is a first-class lever?

effort force and resistance force are on opposite sides of the fulcrum

What is mechanical advantage for a first-class lever?

it varies

What is a second-class lever?

effort force and resistance force act on the same side of the fulcrum, but resistance force acts between fulcrum and effort force

What is mechanical advantage for a second-class lever?

always greater than 1

What is a third-class lever?

effort force and resistance force are on the same side of the fulcrum but the effort force acts between the fulcrum and the resistance force

What is an example of a first-class lever?

seesaw or overhead tricep extension

What is an example of a second-class lever?

wheelbarrow or push up

What is an example of a third-class lever?

a bicep curl

What class lever is most common in the body?

third-class

What are the disadvantages and advantages of body movement being a third-class lever?

disadvantage in force production but increased ROM and flexibility

What hip position produces the weakest torque output?

coxa valga

What is equilibrium?

a state where all forces and torques are balanced

What does unequal forces imply?

the object is accelerating or decelerating

What sign is clockwise torque?

positive

What is center of mass?

the point around which a body’s mass is equally distributed in all directions and the sum of all torques is zero

What direction does the COM shift for an asymmetrical object

towards the larger mass

Where does a body’s weight vector run?

through its center of mass

How does unrestricted squatting affect COM and torque?

COM is farther from knee and increases torque on knee

What does restricted squatting do to torque?

decreases knee torque but increases hip torque

What is a reaction board?

a board with counter weights and a lever to solve for COM

What is the segmental method?

breaking down the body into different segments to calculate for overall COM

What is segment mass and COM data based off of?

cadaver research

What are problems with cadaveric data?

may not include racial or age differences, and may vary depending on athlete or sport

What is the Hanavan model?

a model with 15 major uniform segments using simple geometric shapes

What is the Hatze model?

includes 17 irregularly shaped segments and requires 242 anthropometric measurements from the subject