Ch 2- Biomechanics of Resistance Exercise

Origin

proximal attachment (toward center of the body)

Insertion

distal attachment (away from the center of the body)

Agonist/prime mover

muscle most directly involved with the movement

Antagonist

the muscle that slows down or stops the movement

synergist

a muscle that assists indirectly with a movement

• are always required to control body motion when the agonist is a muscle that crosses two joints

First class lever

Fm and Fr are on opposite sides of the fulcrum

Second class lever

Fm and Fr are on same side of fulcrum, with Fm acting through LONGER moment arm than Fr

• required Fm < Fr

Third class lever

Fm and Fr are on same side of fulcrum, with Fm acting through SHORTER moment arm than Fr

• MA is <1.0, so Fm > Fr to produce torque that is sufficient for contraction

Sagittal plane

left/right halves

• ex. would be bicep curl

Frontal/coronal plane

front/back halves

• ex. would be lateral raise

Transverse plane

upper/lower halves

• ex. would be dumbbell fly (lying) or twist of trunk

What is acceleration?

change in velocity with respect to time

What are impulse and momentum?

F x change in time = m x change in velocity

What is the most relevant metric for a system wide view of an athlete?

impulse

Mechanical energy is the sum of what?

potential energy and kinetic energy

potential energy?

m x g x h

Kinetic energy?

½ m x v²

Power is what?

How quickly work is performed

• power equals the amount of work divided by the time over which the force is applied

• peak power is highest instantaneous power achieved at sample rate of 1/1000 of a second

Angular displacement is?

subsequent movement of a force required to move a body segment multiplied by length of body segment and the sine of the joint angle

• measured in radians

What is angular velocity?

rate of angular displacement

How many degrees is 1 radian?

57.3 degrees

How does neural control affect maximal force output?

Through recruitment and rate coding

Recruitment

which and how many motor units are involved in a muscle contraction

Rate coding

the rate at which the motor units fire

What is more related to the force a muscle can exert rather than volume?

cross sectional area

What occurs to titin during eccentric muscle actions?

the increase in calcium concentration in the sarcoplasm causes it to tighten

• this helps in force production and aligns myosin filaments to increase potential crossbridge sites

• Too few sites when muscle is over contracted, actin filaments overlap excessively

What happens to torque capability as angular velocity increases?

torque capability declines as angular velocity increases

• as joint velocity increases, maximal torque capability increases until about 90 degrees per sec after which there is a gradual decline

Classic formula

load lifted is divided by body weight to the two thirds power

Why are mass and weight used interchangeably incorrectly?

people mistake mass for weight. Things can have the same mass regardless of where they are, however different gravitational pulls can cause different locations to make something weigh differently on the moon vs on earth

Forward inclination of the trunk…

brings the weight horizontally closer to the knees, further from the hip. This is easier on the knees, harder on the hips as the hips are now further from the resistive force. Ex. low bar squat

when trunk is more upright..

the stress is now placed on the knee extensors (quads) and the moment arm is closer to the hip joint

Advantages of weight stack machine

• safety

• design flexibility

• ease of use

advantages of free weights

• total body training

• simulation of real life activities

what did nautilus create?

a machine that uses a cam of variable resistance to match the torque capabilities of muscle

bracketing technique

athlete performs sport movement with less than normal and more than normal resistance

power exercises like snatch/clean and jerk are effective for what?

improving ability to produce high accelerations against heavy resistances

Friction resisted exercise devices require what type of force to initiate movement?

a relatively high force, then relatively constant force afterwards to continue movement

why does it take more force to get the sled moving than it does to keep it moving?

the coefficient of static friction will always be greater than the coefficient of sliding friction

85-90% of intervertebral disk herniations occur between what vertebrae?

the two lowest lumbar vertebrae (L4 ad L5) or the lowest lumbar and top sacral vertebra (L5 and S1)

What spine position is best for minimizing L5/S1 compressive forces/ligament strain?

normal lordotic lumbar spine position

normal vertebral column position?

s shaped

slightly rounded (kyphotic) in thoracic spine (posterior curve)

lordotic in lumbar spine (anterior curve)

what do knee wraps provide for lifters?

provide direct help in extending the knee