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Muscle's have different shapes.  A muscle's shape will affect its ability to produce force. 

Match the 7 muscle shapes to its corresponding muscle.








Fusiform - biceps brachii

Parallel - rectus abdominis

Convergent - pectoralis major

Unipennate - palmar interosseous

Bipennate - rectus femoris

Multipennate - deltoid

Circular - orbicularis occuli 


Match the correct answer.

1. Type 1 Muscle fibers

2. Type 2A Muscle fibers

3. Type 2b muscle fibers



a) Low fatigability, fast mechanical speed, moderate twitch tension, medium motor unit size, MU type fast fatigue resistant, fast oxidative glycolytic

b) Fast glycolytic fiber type,  fast fatigable MU type, large MU size, high twitch tension, fast mechanical speed, high fatigabiilty

c) low fatigability, slow mechanical speed, low twitch tension, small MU size, slow MU type, Slow oxidative fiber type. 


Define muscle force, using the force-velocity graph

Which type of muscle contraction generates the most force? 




Muscle force: is the ability of the muscle to generate movement (push or pull) 

Concentric contraction: as the velocity increases the force decreases. If muscle force is greater than the load, the muscle will contract in a shorten position. To generate more tension, you should slow down the speed of contraction. 

Eccentric contraction: As the velocity of lengthening. increases, the tension increases up to a point. 

Isometric contraction: force is equal to load, V=0




What is passive tension? (Length-tension relationship-isometric)

When the muscles is passively lengthened the tension will increase as the muscle reaches its outer range. 


Name and describe the different sheaths in the skeletal muscle? 

What is their role?




Are connective sheaths that surround the various divisions of the muscle ..are all linked together and are importat in the transmission of passive forces through a muscle, such as when a muscle is stretched. 


What gives the striated appearance of muscle fibers?

saromeres lined up along the fiber length


How do the thick and thin filaments generate muscle contraction?

Myosin is the motor protein that when allowed to bind to actin, it pulls the actin toward the center.  The actin molecule, is a twisted bundle of bubbles and at either end is attached to a Z-plate. When myosin tugs on actin, it causes the thin filament to move, pulling the ends of the sarcomere closer together.  



A muscle contraction consists of a series of repeated events. First, calcium triggers a change in the shape of troponin and reveals the myosin-binding sites of actin beneath tropomyosin. Then, the myosin heads bind to actin and cause the actin filaments to slide. Finally, ATP breaks the actin-myosin bond and allows another myosin 'oar stroke' to occur. Repetition of these events causes a muscle to contract.




length tension relationship of a contractile unit


Describe that our muscle have an optimal length to produce maximal force. 

The strength of muscle contraction is influenced by the initial length of muscle fiber. 


muscle that is in an lengthened position: few myosin actin crossbridges could form as the overlap is small

Shortened position:  too much overlap and the myosin filaments cannot move any further down the thin filaments as the Z disc is in the way.  

Valid for isometric contraction only when no movement occurs. 


(in other words, when a muscle is in a lengthened position there are very few crossbridges between the myosin and actin, as the overlap is small, and muslce is unable to generate much tension. Similarly if the muscle is in a shortened psoition, there is too much overlap, and the myosin filaments cannot move any further down the thin filanents as the Z dis is in the way which liits tension) 


What is a tetanic contraction?

Differenced between tetanic and a twich summation?

is a prolonged contraction of a muscle (with no relaxation) and only stops when the stimulus stops or the muscle fatigues. 

A twitch summation occurs when the muscle is stimulated before it has a chance to completely relax. A temporal contraction is the addition of a second twitch resulting in greater tension. 


What is the tropomyosin-Troponin Complex?
How does Troponin Complex get activated?



Prevents the muscles from continued contraction

Tropomyosin is a rope like proten that wraps around actin, preventing myosin from grabbing it. Tropomyosin is like the guard in a muscle cell.  It blocks myosin, until the muscle should contract.  How does the muscle know when to contract?  

  Troponin - is a protein that can move the tropomyosin off the myosin binding site on the actin.  Essestially, troponin gives tropomyosin a tap on the shoulder to  move when it receives the signal from calcium.

 Muscle cells receives electrical messages in the forms of action potential. When the AP arrives at the muscle cell, it triggers a release of calcium ions. the released calcium then bind to the troponin complex and activates it. Trypomyosin gets the boot, then the muscle can contract. 


Provide an example of a fusiform shaped muscle 

Biceps brachii

Fusiform muscles are spindle like, it's wider in the middle and narrow at either ends. 


What are the two principles of muscle gradation force?

Size principle: the order of motor unit recruitment 

Summation or frequency (the amount of stimulation that the motor unit received affects whether the muscle fibers just twitches or produces a full force of muscle contraction


What is Summation (Frequency of recruitment)?


Summation (Frequency of recruitment) is another mechanism by which the nervous system gradate muscle force. 

Essentially, low frequencies of stimulation will generate a single twitch of the motor unit…to a few twitches. As the frequency increases, the sum of muscle twitches will increase the force (typically above 80 hertz).




Give 2 reasons why it is important to measure muscle strength.

1. to determine if there is any deviation from the normal

2. to assess wehther the condition is getting wrose or better or remain the same. 

3. to give a baSe meaSurement to the muscle condition. 

4. to assess whether any treatment you implement is having a positive or neg. effect. 


Describes the components of the sarcomere. 

Z line, I band, A band, H zone, M line. 

Z line: determines the zones of one sarcomere

I band: the area where the thin and thick filaments do not overlap

A band: formed by the dark thick filaments, with areas overlapping with the thin filaments

H zone: the area of the A band where the thick and thin filaments do not overlap. 

The M line is the center of the sarcomere, which is between the H zone and the A band. 

The A band is the area formed by myosin and actin.


Describe passive tension

- Passive tension is the resistance that the muscle tissue has to being passively stretched 

While the passively stretched muscle approaches the outer range,  the tension in the muscle increases without the muscle being active.


The tension increases as the muscle is taken from mid-range to outer range, possibly to stop the sarcomere from being overstretched. 



The area where thin and thick filaments overlap is called the: 

A- band


How is muscle forced controlled?

- increasing  in  the number of motor units activated (size principle) 

- increasing in the frequency of stimulation (summation)



(eg., low frequencies of summation =  single twitch

the sum of the frequency will result in increased muscle contraction - tetanus summation


a muscle fiber is a made up of lots of _______lying parallel to each other



Define muscle work involves?


The amount of work a muscle could produced is equal = force x distance


What is the force-velocity relationship of skeletal muscle?



Could be defined as the speed in which the muscle changes length and produces force.

Force of contraction = load  --> no change velocity, no change in muscle length - and a isometric contraction occurs. 

Concentric contraction =   "and increase in the speed of contraction will lead to a decrease of the force that is generated by the muscle" . -- the greater the speed, the less force is required to overcome the load. This happens because - the rate of crossbridge cycle also increases, leaving less crossbridge possible at a certain time. 

Eccentric contraction = " as velocity increases so does the force, up until a certain point


How does the arrangement of the sarcomere influence muscle force production compacity?

The greater the number or sarcomeres in parallel (rather than in a straight line) the greater the force generation compacity of the muscle because this arrangement allows the force to be transmitted directly. 



What is a fascicle?

A fascicle is a bundle of muscle fibers and is held together by perimysium. A group of fascicle form a muscle and is held together by epimysium. 


What are myofibrils?

they are elognated contractile threads found in striated muscle cells. 

- Myofibrils are composed of thin and thick myofilaments arranged in a precise fashion that enables them to slide in relations to each other.





Describe Strap and fusiform muscles. Provide an example of each.

- Strap have a tendon at either end and relatively long muscle fibres that run between the tendons. The muscle fibres are arranged in parallel to or are very similar to the angle of pull of the tendon. 

Eg., of Strap muscles:  Sartorious


- Fusiform muscles are wider and cylindrically shaped in the center and taper off at the ends. This overall shape of fusiform muscles is often referred to as a spindle

Eg., of Fusiform muscles: biceps brachii 


What is aerobic capacity (endurance) dependent on?

The muscle's ability to resist fatigue



Explain Unipennate vs bipennate vs multipennate muscle fibers

Give an example of each


Unipennate and bipennate  muscles have a central tendon into which short muscle fibres are inserted. The fibre direction is different to the angle of pull of the tendon. Unipennate muscle fibres are on the same side of the tendon, eg. palmar interossei,  wherease bipennate muscles has fibers on both sides of the tendon, rectus femoris. And deltoid muscles are multipennate

Triangle muscles display mixed characteristics.


What molecule is needed to break the contraction of muscles. So it could relax

ATP is required to disrupt the myosin-actin interaction and prepare the system for another 'oar stroke.' Repetition of these oar-like myosin strokes constitutes a muscle contraction. Note that the bond between actin and myosin is so strong that it requires an input of energy via ATP to break the bond. This explains why muscles stiffen shortly after death. Without a steady supply of ATP to break the actin-myosin bond, muscles stay contracted in a process known as rigor mortis.


What is muscle endurance? What is it dependent on?

Define Fatigue.  What are the sources of fatigue?

The muscle's ability to resist fatigue and is dependent on muscle's aerobic compacity, their ability to use oxygen to produce energy.

In other words, muscle endurance is defined as the abilty of a muscle to maintain isometric contraction or continued dynamic contractions.  


The inability of the muscle to sustain a force (contraction).


1) diminish response to stimuli

2) depletion of energy.

3) build up of metablic waste


What affects muscle strength?

Length tension relationship of a contractile unit (isometric) - generate greater force in contraction/tension

Force-velocity relationship (concentric) - the greater the velocity of contraction, the smaller the tension in the muscle. 




Discuss the sliding filament theory


" The sliding filament theory explains how the actin and myosin protein fibrils slide over one another and form a series of crossbridges that rotate and pull the sarcomeres closer together, thus shortening the muscle and producing force."


What is a sarcolemma?

Is the cell membrane of a striated muscle fiber. 


Explain the role of calcium ions on muscle contraction.

- Calcium ions binding to the troponin change its shape, which in turn pulls the tropomyosin out of the way of the binding site, allowing the myosin head to attach to the actin. Once attached to the actin, the myosin neck flexes, pulling the thin filament along. This flexing has the effect of sliding the thick and thin filaments over each other. 


Define muscle power

Muscle Power is the rate at which work is being done.

= Force (of contraction) x velocity (of contraction)


Define muscle power

Muscle Power is the rate at which work is being done.

= Force (of contraction) x velocity (of contraction)

Velocity is the distance of contraction 

Power = net joint moment x joint angular velocity. 

(Aerobic vs anaerobic power depending whether type 1 or 2 fibers are recruited)


Which physiological process has to occur for muscle strength to increase?

- Increase in actin and myosin (muscle stimulated is relayed to CNS which in turns stimulates the ribosomes to replicdate more A & M). As a result myofibrils increases in length and width. 

- The number of myoctye increases

-The size and the number of sarcomeres increases

- Increase in density of mitochondria within muscle tissue (increaSe in glycogen, cP, ATP substrate)

- Increase concentration and activity of glycolytic enzYmes, myokinase and creatube phosphokinase (the enzymes needed for growth)

4 weeks process



Stages of Summation 

Stages of Summation 

A few fibers twitching (5 Hz) 

Temporal Summation (20 Hz)

Unfused Tetanus (80 Hz)

Fused Tetanus (100 Hz)


What is a sarcomere?

A sarcomere is the smallest functional unit of contraction, which is formed by protein filaments arranged in a precise way to produce muscle contraction. 


The arrangement of alternating bundles of thick and thin filaments stacked in a long line produces the the straited appearance of muscle tissue and allows the column to change lentgth


What are the main differences between strength and endurance training?

Cardiovascular endurance is measured by its VO2 max which is function of intensity. Intensity is prescribed through heart rate. Local muscle endurance is measured by the length of time the muscle can function before fatigue occurs or the muscle ability to recover after a workout. 


High repetitions against low resistance is necessary for increased endurance.


Strength gains requires high loads and low reps


What physiological factor could affect the range of movement the muscle could work through and speed of contraction?


The number of sarcomeres in series. The more sarcomeres in series is able to shorten through a greater range and at a greater velocity compared with the muscle with less. The more you trained, the more sarcomeres you'll add to your muscle fiber, the greater your strength would be because of the ability of your muscle to produce force. 


Muscle Force?

Versus muscle strength?

muscle force:  ability of muscle to move the body part, or object, to push or to pull

Muscle strength: is the forced produced by a muscle that can be measured




What is the difference between  the different types of pennate muscles -- bipennate, unipennate or multipennate muscle shape?

Provide some examples of each type.

Unipennate: all the fascicles are on the same side of the tendon, include certain muscles in the hand eg, palmar interosseous. 

 Bipennate: the fascicles are on both sides of the central tendon, the pennate muscle is called bipennate. Example: Rectus Femoris

Multipennate: muscles have multiple rows of diagonal fibres, with a central tendon which branches into two or more tendons. An example is the Deltoid muscle which has three sections, anterior, posterior and middle.


What is a muscle twitch?


Type 1 fibers has a low twitch tension, is that true?

It is a very low level muscle contraction resulting from a low frequency stimulation


Type 1 fibers: low, 

Type 2: moderate

Type 3: high



What is the size principle? 

Explains that the motor units within a muscle are recruited in a set order according to the force needed for the task

1) Recruitment of smallest motor units;  Type I fibers (slow oxidative, slow to fatigue, low force, slow force production rate, has low twitch tension ) are recruited first. 

2) Recruitment of medium size MU;  Type IIA are recruited to increase the amount of force. Type 2a fibers are glycolytic. They can withstand fatigue, produces moderate amount of twitch tension, fast. 

3) Recruitment of the bigger MU are last.  Type IIB fibers are fast glycolytic, can generate a lot of force/power, due to ability to twitch fast, but they fatigue very quickly. recruited



Define the length tension relationship of a muscle


Explains that the muscle is strongest is when it is holding a contraction somewhere in the mid-range of motion rather than when it is fully shortened or fully lengthened. 




How does the length tension relationship explains force production? 

Production of force by a muscle is proportional to the number of crossbridges that occur between the actin and myosin. Therefore, if a muscle is in a lengthened or shortened position the number of cross-bridges that can occur are reduced and therefore the force generated is smaller (active tension)


Define muscle power

is the rate at which work is being down and is calculated by the equation for power

Muscle Power = force of contraction x velocity of contraction


Muscle twitch versus contraction

In summary, a muscle twitch is a single contractionresulting from a threshold stimulus, where a threshold stimulus is the smallest stimulus strength that actually results in a contraction. ... Our postural musclesproduce tetanic contractions, thus maintaining posture for long periods of time.