Muscle Mechanics Flashcards
Biomechanical Muscle Model
passive components (elastic) are both in series and in parallel with the contractile unit; think of an electric circuit
Series Elastic Component
tendons, bone, titin
Parallel Elastic Component
endomysium, perimysium, epimysium;
Isometric Contraction
whole muscle length remains constant; internal moment = external moment
Concentric Contraction
whole muscle shortens and internal moment exceeds external moment
Eccentric Contraction
whole muscle lengthens; internal moment is less than external moment
Fusiform Muscle
fibers run parallel to each other and to the central tendon
Pennate Muscle
fibers at an angle to the central tendon; pennation angle decreases muscle force through tendon
Physiological Cross Sectional Area
pennate muscles have a greater PCSA, thus more force
Length-Tension Properties
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
Force-Velocity Properties
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)
Force-Velocity Cruve
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
What factors can we influence for a muscle?
length of sarcomere
speed of loading
motor unit recruitment (increase number or type or size or speed of firing)
type of contraction
moment arm
Flexibility-Positioning
relax the mm; isolate it and stretch based on position; relieve any tension off of the muscle
Flexibility- Autogenic Inhibition
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
Flexibility-Reciprocal Inhibition
contract opposite side of joint to get inhibition of the muscle that is the agonist
Flexibility-Stretch Reflex
not good; quick stretch that leads to contraction instead of relaxation
Aging Impact on Skeletal Muscle
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
Bi-Articular Muscles
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
Active Insufficiency
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
Passive Insufficiency
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
