Muscle Mechanics

Question 1

Biomechanical Muscle Model

Answer 1

passive components (elastic) are both in series and in parallel with the contractile unit; think of an electric circuit

Question 2

Series Elastic Component

Answer 2

tendons, bone, titin

Question 3

Parallel Elastic Component

Answer 3

endomysium, perimysium, epimysium;

Question 4

Isometric Contraction

Answer 4

whole muscle length remains constant; internal moment = external moment

Question 5

Concentric Contraction

Answer 5

whole muscle shortens and internal moment exceeds external moment

Question 6

Eccentric Contraction

Answer 6

whole muscle lengthens; internal moment is less than external moment

Question 7

Fusiform Muscle

Answer 7

fibers run parallel to each other and to the central tendon

Question 8

Pennate Muscle

Answer 8

fibers at an angle to the central tendon; pennation angle decreases muscle force through tendon

Question 9

Physiological Cross Sectional Area

Answer 9

pennate muscles have a greater PCSA, thus more force

Question 10

Length-Tension Properties

Answer 10

maximum total tension occurs at 1.2x resting length for a single fiber; this is because as the muscle is stretched past its resting length, passive components begin to resist the stress, adding tension to the normal peak at resting length;

assumes 100% recruitment, a single muscle fiber, and isometric contraction

Question 11

Force-Velocity Properties

Answer 11

concentric behavior due to time for cross bridge cycling; as velocity increases, less time for tension development, so can’t contract as effectively;

Assumptions: 100% recruitment, single muscle fiber, load is held constant (isotonic)

Question 12

Force-Velocity Cruve

Answer 12

as you lengthen more rapidly, the force that is able to be produced goes up (“neg” side of curve; eccentric contraction); big increase due to passive structures taking some of the load

during isometric contraction, the force developed is about midrange; 0 speed

During concentric contraction, as you contract more quickly, the max force able to be produced goes down; the limiting factor has been thought to be due to cross bridges being unable to reattach in time

Question 13

What factors can we influence for a muscle?

Answer 13

length of sarcomere
speed of loading

motor unit recruitment (increase number or type or size or speed of firing)

type of contraction

moment arm

Question 14

Flexibility-Positioning

Answer 14

relax the mm; isolate it and stretch based on position; relieve any tension off of the muscle

Question 15

Flexibility- Autogenic Inhibition

Answer 15

Golgi tendon organ; as you contract the mm, you get inhibition of mm after contraction;

Ex: contracting hamstrings, then relax them and you can go further into the stretch

Question 16

Flexibility-Reciprocal Inhibition

Answer 16

contract opposite side of joint to get inhibition of the muscle that is the agonist

Question 17

Flexibility-Stretch Reflex

Answer 17

not good; quick stretch that leads to contraction instead of relaxation

Question 18

Aging Impact on Skeletal Muscle

Answer 18

increased adipose tissue, lower neuromuscular activation (loss of MN, poor coordination), selective atrophy of Type II fibers, lose 1% muscle mass per year after age 40, muscle strength decreases 3x faster,

exercise can slow this process

Question 19

Bi-Articular Muscles

Answer 19

functional advantage: coordinates movement via fine tuning and coordination of movement; transfers force from proximal joint to distal joint to allow for adequate force distribution;

tends to not be used for power but for stability

Question 20

Active Insufficiency

Answer 20

multi joint muscle unable to contract forcefully in a shortened position; has to do with CONTRACTION; muscle starts out at too short a length so they don’t have enough distance to shorten to create tension

Question 21

Passive Insufficiency

Answer 21

multi-joint muscle is unable to be stretched sufficiently to produce a full range of motion in all the joints simultaneously; hamstrings cannot stretch enough to to allow both maximal hip flexion and maximal knee extension