Muscle Mechanics 1 Flashcards

1
Q

Isometric Contractions

A
  • when a muscle develops tension, but stays the same length because its ends are attached to immovable objects, the contraction is isometric
  • length stays the same but tension increases
  • work is not done because the load is not moved
  • power is zero since work is 0
  • involved in maintaining posture
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Stretching Series Elastic elements

A
  • stretching of series elastic elements offsets contractile element contraction so there is no movement of load during isometric twitch
  • series elastic elements are represented as springs and can be thought as the rubberband-like tendon, although the entire muscle contributes to SE
  • upon activation of actin and myosin, and cylcing of the cross bridges, the contractile element shortens while the series elastic elements elongates by an equal distance
  • the degree of shortening of the contractile element equals the degree of elongation of the series elastic thereby keeping the overall length of the muscle fiber constant (isometric)
  • this sequences of events reverses during relaxation phase of an isometric contraction
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Body movements require both isometric and isotonic contractions

A
  • lifting a book
  • isotonic- bicep, length change (concentric/ecentric) tension sustained, body movement = book movement
  • isometric-back-length constant, tension changes, no movement, postural
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Isotonic contractions

A
  • when the force of contraction of the muscle is at least equal to the load so that the muscle shortens, the muscle is said to contract isotonically
  • the tension curve for an isotonic twitch shows a plateau during which the force or tension is constant
  • the tension curve resulting from an isotonic twitch will look different depending upon the load placed on the muscle
  • the greater the load the higher the plateau and the greater the time lag between stimuli and the start of muscle shortening
  • if the load exceeds the amount of force the muscle can generate, an isometric twitch results
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Shortening and Force during an Isotonic twitch

A
  • upon activation of actin and myosin and cycling of cross bridges the contractile element shortens and series elastic element elongates
  • once tension builds up to the point it equals (or lightly exceeds the load, the load begins to move
  • then the tension becomes constant
  • further shortening of contractile will lift the load, but while the load is being lifted the tension is constant
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Four stages of an isotonic twitch

A
  • isometric tension development- tension develops without shortening until the force developed equals the load
  • isotonic shortening- shortening of the muscle at constant tension
  • isotonic relaxation- elongation to the initial length at constant tension
  • isometric relaxation-reduction of tension at the initial length
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Isotonic twitch as a function of load

A

-for isotonic twitches with heavier loads- longer delay (latency) until shortening occurs, initial velocity of shortening,distance of shortening decreases and muscle drops the weight sooner

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Isotonic contraction analysis provide load-velocity info

A

-when a muscle contracts isotonically under increasing loads the contractions display the following effects in the distance shortened vs time plot- the latent period (time lag between stimulation and shortening) increases, the duration of shortening decreases, the velocity of shortening decreases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Po of different muscles

A

Po is the maximal isometric tension that can be generated at a given initial length, and a given state of contractility

  • Po is a function of the number of force generating cross-bridges that can be formed
  • the larger the muscle, the larger the number of cross bridges and the larger is Po
  • in skeletal muscle Po can increase with frequency modulation, recruitment of additional motor units, and with initial lengths closer to the optimal initial length Lmax, but not by changes in contractility
  • in cardiac muscle, Po can increase with an increased initial length, and by increased contractility, but not recruitment
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Myofibers produce maximum work and power at intermediate loads

A
  • the speed with which a muscle contracts is also important in movement
  • when a muscle is contracted isotonically under successively increasing loads the contractions display the following effects: the latent period (time lag between stimulation and shortening) increases, the duration of shortening decreases, the velocity of shortening decreases
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Preload and afterload during an isotonic contraction

A
  • preload is the load required to stretch a muscle from its resting length
  • recall that muscles normally operate between 100-115% of resting length, so some load is required to stretch the muscle into its operating range
  • once the 1g preload is added and the muscle stretched, the 2g afterload is then added and the muscle is stimulated causing the movement of the preload and the afterload
  • the preload+afterload = total load
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Skeletal muscle contraction cycle for an isometric contraction

A
  • tension develops at constant length to a maximal tension for that particular initial length
  • decrease of tension to 0g at constant length
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Skeletal muscle contraction cycle for isotonic contraction

A
  • development of tension at constant length until the tension equals the load
  • shortening during the lifting of the of load at constant tension
  • lengthening at constant tension during the beginning of relaxation
  • decrease of tension during relaxation at constant length
How well did you know this?
1
Not at all
2
3
4
5
Perfectly