Skeletal Muscle Mechanics Flashcards
What are the determinants of muscle force production?
recruitment of motor units, muscle fiber type, muscle length, speed of contraction, muscle action, torque potential, muscle architecture, firing frequency, fatigueability
Describe the recruitment of motor units.
size principle - recruit small ones first then move up to larger as needed
Classify each type of muscle fiber by the functional classification (oxidative capacity).
Type I - slow oxidative,
Type IIA - fast oxidative glycolytic,
Type IIx - fast glycolitic
Classify each type of muscle fiber by the diameter size.
Type I - small,
Type IIa - intermediate,
Type IIx - large
Classify each type of muscle fiber by the color.
Type I and IIa - red,
Type IIx - white
Classify each type of muscle fiber by the capillary density.
Type I and IIa - dense,
Type IIx - sparse
Classify each type of muscle fiber by the myoglobin content.
Type I - high,
Type IIa - intermediate,
Type IIx - low
Classify each type of muscle fiber by the speed of contraction.
Type I - slow,
Type IIa and IIx - fast
Classify each type of muscle fiber by the rate of fatigue.
Type I - slow,
Type IIa - intermediate,
Type IIx - fast
What is the most important characteristic of muscle?
the ability to develop tension and to exert a force on the bony lever
What is passive tension?
developed in the parallel component of the muscle, created by lengthening the muscle beyond slack length of the tissues
What is active tension?
tension developed by the contractile elements of the muscle
At which sarcomere length is isometric tension maximal?
at optimal length
At which sarcomere length is isometric tension decreased?
lengthening beyond optimal length AND shortening beyond optimal length
What describes the relationship between the velocity of a muscle contraction and force produced?
force-velocity relationship
The force-velocity relationship provides an explanation for what type(s) of contractions?
concentric and eccentric
During which contraction is the muscle shortening?
concentric
During which contraction is the muscle lengthening?
eccentric
What is it called when the whole muscle is activated and the bones to which it attached do not move?
Isometric contraction
What happens to the bones in a concentric contraction?
move closer together
What happens to the bones in an eccentric contraction?
move away from each other
True/False: The amount of tension that can be developed in a muscle depends on the type of contraction.
True
What are the factors affecting torque potential?
length of moment arm of muscle force,
length of the muscle,
Velocity of shortening or lengthening during dynamic movements
Which of the following is true?
a. muscles produce force by active over a moment arm at the joint to produce torque
b. moment arm of the muscle can’t change with joint position
c. As the joint moves, the muscle length remains constant.
A is true.
B = can change which affects the torque produced
C = muscle length changes
What is the reduced capacity in production of active tension across a joint occurring when muscles are placed on slack across another joint?
active insufficiency
Describe an example of active insufficiency.
can’t keep a tight fist when moving from neutral position to flexion
What occurs when an inactive, potentially antagonistic muscle is of insufficient length to permit full ROM at the joints crossed by the passive muscle?
passive insuffieciency
Describe an example of passive insufficiency.
fingers curl when moving from wrist Ext to Flex
What is the electrical activity of a muscle force (measured my an EMG) proportional to?
recruitment (which is proportional to muscle force)
What are the advantages and disadvantages of isokinetic exercise and testing?
advantages: maximal loading thru ROM, safe, objective, reproducible measurement
Disadvantages: isolation, non-WBing, limited acceleration, mono-planar, cost, not functional, differences in exertion by performer
Describe an example of the utilization of active insufficiency to isolate a muscle group.
both Gmax and hamstrings perform hip extension when knee is maintained in extension, but when knee is flexed, it puts the hamstrings in active insufficiency, giving preference to utilizing Gmax
Passive insufficiency leading to tenodesis can allow what?
individuals (such as C6 quadriplegic) to regain a degree of functional opening of their hand while reaching (move wrist into flexion = fingers straighten/release) and closing of their hand for grasping (moving wrist into extension = fingers curl/grasp)
