Biomechanics of skeletal muscle
muscle cramps (what are they caused by, how can we prevent them)
-Electrolyte imbalances, deficiencies in calcium and magnesium and dehydration -Stretch -More Sodium -Ease into a Workout Program
FT fibers- what type of muscle contraction, and what type of activities?
-fast powerful muscular contraction -good for sprinting, and jumping
what is a motor unit?
-single motor neuron and all fibers it innervates -considered the functional unit of the neuromuscular system -100 - 2000 fibers
type 1 slow twitch fibers (oxidative) (contraction speed, fatigue rate, diameter)
-slow -slow -small diameter
what is muscular endurance?
-the ability of muscle to exert tension over a period of time -the opposite of muscle fatigability
what is muscular power? (2 equations and 1 def)
-the product of muscular force and the velocity of muscle shortening (F×V) -the rate of torque production at a joint -the product of net torque and angular velocity at a joint (M×ω)
why are series and parallel elastic components named as they are?
-they are named this because the membranes and tendons are either parallel, or in series (in line) with the muscle fibers, which provides the contractile component
how can the elastic components exert significant influences on the production of muscle force, power, and work?
. During quick, rapid movements, they can increase muscle power by storing the work of muscle contraction and releasing it rapidly. Alternatively, the elastic components can release energy more slowly to stretch the muscle contractile component during an activity such as landing from a jump, dissipating energy, and serving to protect the muscle from damage
4 properties of musculotendinous unit?
1-extensibility 2-elasticity 3-irritability 4-ability to develop tension
common muscle injuries (5)
1-strains 2-contusions 3-cramps 4-delayed onset muscle soreness 5-compartment syndrome
The length of electromechanical delay (EMD) is?
20-100ms between stimulation and initiation of tension The length of EMD varies considerably among human muscles, with values of 20-100 msecreported (21). Researchers have found shorter EMDs produced by muscles with high percentages of FT fibers as compared to muscles with high percentages of ST fibers
Delayed-Onset Muscle Soreness
24-72 hrs after exercise micro-tearing of the muscle tissues
A muscle directly involved in causing a segment to move is called what? A.agonist B.antagonist C.neutralizer D.stabilizer
A
A single muscle cell is called what? A.fiber B.neuron C.unit D.none of the above
A
During the first 12 weeks of resistance training, strength gains are due primarily to what? A.improved innervation of the muscle B.increase in cross-sectional area C.both A and B D.none of the above
A
During the kicking and follow-through phases of a punt, the quads are experiencing what type of contraction? A.concentric B.eccentric C.isometric D.isokinetic
A
In which of the following activities do the biceps brachii function as antagonists? A.straightening the elbow during a push-up B.straightening the elbow during a pull-up C.curling a barbell from the floor to waist height D.both A and B
A
When the wrist is flexed, the finger flexors cannot produce as tight a fist as when the wrist is in a neutral position. This is an example of what? A.active insufficiency B.passive insufficiency C.both A and B D.none of the above
A
Where is the series elastic component (SEC) of a muscle found? A.tendons B.ligaments C.muscle membrane D.all of the above
A
Which of the following is a unique behavioral property of muscle tissue? A.ability to develop tension B.extensibility C.irritability D.all of the above
A
Which of the following statements is true? A.When movement is slow, slow twitch fibers are recruited first. B.When movement is fast, fast twitch fibers are recruited first. C.Both A and B are true. D.None of the above are true.
A
Which of the following types of muscle tension is commonly used as a braking mechanism to slow limb movement? A.eccentric B.isotonic C.concentric D.isometric
A
bi-articular muscle
A muscle that crosses two joints
A contraction in which there is not a change in length is called what? A.dynamic B.isometric C.concentric D.isokinetic
B
During the down phase of a knee extension exercise, what role does the hamstring group play? A.agonist B.antagonist C.stabilizer D.neutralizer
B
Muscle hypertrophy in humans is primarily due to what? A.increase in number of muscle fibers B.increase in size of muscle fibers C.both A and B D.none of the above
B
The component force which is parallel to the moving bone and acts to pull the bones together at the joint is called what? A.curvilinear force B.stabilizing force C.rotary force D.dislocating force
B
The elasticity of human skeletal muscle tissue is believed to be due primarily to which of the following? A.the parallel elastic component B.the series elastic component C.the continuous elastic component D.the active elastic component
B
The opposite of muscular endurance is what? A.muscular strength B.muscular fatiguability C.muscular power D.muscular flexibility
B
What type of muscle contraction is employed by the elbow flexors when slowly lowering your backpack to your desk? A.concentric B.eccentric C.isometric D.isokinetic
B
Which behavioral property of muscle tissue is defined as "the ability to respond to a stimulus"? A.elasticity B.irritability C.extensibility D.contractility
B
Which of the following does not characterize a pennate muscle? A.relatively strong B.fibers parallel to long axis of muscle C.relatively low range of motion D.all of the above are true
B
Which of the following is/are characteristic of fast-twitch oxidative glycolytic fibers? A.Contraction speed is intermediate (faster than type I but slower than type IIB). B.Fatigue rate is intermediate (faster than type I but slower than type IIB). C.both A and B D.none of the above
B
Which of the following most accurately describes a motor unit? A.a single muscle fiber and a single motor neuron B.a single motor neuron and all muscle fibers it innervates C.a single muscle fiber and several motor neurons D.none of the above
B
Which of the following statements represents the force-velocity relationship for muscle tissue? A.contraction is faster when the load is heavier B.contraction is slower when the load is heavier C.contraction is slower when the load is lighter D.the speed of contraction is not affected by the nature of the load
B
Which of the following terms best describes the rate of torque production at a joint? A.mechanical work B.muscular power C.muscular energy output D.muscular strength
B
Which of the following types of strength training is particularly associated with subsequent muscular soreness? A.concentric B.eccentric C.isometric D.all of the above
B
During the execution of a pull-up when the chin is over the bar, which force exerted by the biceps brachii is greatest at the elbow? A.the rotary force B.the stabilizing force C.the dislocating force D.the "pinching" force
C
In human skeletal muscle, force generation capability is highest in which of the following conditions? A.muscle is at resting length B.muscle is slightly shortened C.muscle is slightly lengthened D.muscle length is irrelevant to force production
C
The amount of torque a muscle group can generate at a joint is used to measure what? A.muscular power B.muscular endurance C.muscular strength D.muscular flexibility
C
The torque of a muscle (rotary component) is greatest in what position? A.when the moment arm is longest B.when the muscle insertion is 90° to the bone C.both A and B D.position does not effect torque
C
Which of the following is a potential disadvantage of multijoint muscles? A.active insufficiency B.passive insufficiency C.both A and B D.none of the above
C
Which of the following likely contributes to the stretch-shortening cycle? A.the series elastic component B.muscle spindle activity C.both A and B D.none of the above
C
Which of the following statements is/are true? A.Pennate muscles are capable of producing more tension per unit of cross-sectional area than parallel muscles. B.Parallel muscles are capable of producing more range of motion than pennate muscles. C.Both A and B are true. D.Neither A nor B is true.
C
Which of the following time periods is termed electromechanical delay? A.the time required for conduction of the nerve impulse to the neuromuscular junction B.the time required for the nerve impulse to cross the neuromuscular junction C.the time required for the muscle to initiate the development of tension after receipt of the nerve impulse D.the time required for a muscle to reach peak tension after the development of tension is initiated
C
Which type of muscle could serve as an antagonist of a flexor? A.abductor B.adductor C.extensor D.rotator
C
compartment syndrome
Compartment syndrome is a painful condition that occurs when pressure within the muscles builds to dangerous levels. This pressure can decrease blood flow, which prevents nourishment and oxygen from reaching nerve and muscle cells. Compartment syndrome can be either acute or chronic. can cause hemorrhage or edema
The force-velocity relationship implies which of the following? A.It is impossible to move a heavy resistance at a fast speed. B.It is impossible to move a light load at a slow speed. C.both A and B D.none of the above
D
When an opposing torque at a joint is greater than the torque created by a muscle, what type of contraction occurs in that muscle? A.isometric B.isotonic C.concentric D.eccentric
D
When flexing the elbow, the biceps brachii, brachioradialis, and brachialis are the three major agonists recruited to perform this movement because all cause flexion at the elbow. However, the biceps also cause supination, an undesired movement. Therefore another muscle acting as a , causing must be recruited to prevent the undesired motion. A.stabilizer, extension B.neutralizer, extension C.stabilizer, pronation D.neutralizer, pronation
D
Which of the following is a behavioral property of muscle tissue? A.ability to develop tension B.extensibility C.irritability D.all of the above
D
Which of the following is true regarding the parallel elastic component (PEC) of muscular elasticity? A.This component is provided by the muscle membranes. B.This component provides resistance when a muscle is passively stretched. C.This is the component primarily responsible for the elasticity of muscle. D.both A and B E.all of the above
D
Which of the following is true regarding the stretch-shortening cycle? A.When a muscle is stretched just prior to contraction, the resulting contraction is more forceful. B.An eccentric contraction is followed by a concentric contraction. C.The SSC promotes storage of elastic energy. D.both A and B E.all of the above
E
Which of the following is/are characteristic of muscle fatigue? A.reduction in muscle force B.reduction in shortening velocity C.prolonged relaxation of motor units between recruitment D.both A and B E.all of the above
E
eccentric strength training
Eccentric strength training involves the use of resistances that are greater than the athlete's maximum isometric force generation capability. As soon as the load is assumed, the muscle begins to *lengthen*
A high percentage of FT fibers is advantageous for generating ____ movements, and a high percentage of ST fibers is beneficial for activities requiring ___.
FT-better for fast movements ST-better for activities involving endurance
what is passive insufficiency?
It occurs when a muscle cannot elongated any farther without damage to its fibers (this is done passively). restriction of joint range of motion when muscles are fully stretched (decreased ROM for wrist extension with the fingers extended inability of a two-joint muscle to stretch enough to allow full range of motion at both joints at the same time
increasing speed, force, or duration of movement involves progressive recruitment of
MUs with higher and higher activation thresholds -smaller then larger (size principle)
what is a myofibril?
Many of these units make up a single muscle fiber. -myofibrils hold actin and myosin and made of many sarcomeres
isometric contraction
Muscle contracts but there is no movement, muscle stays the same length (pushing into a wall, not moving)
high-frequency stimulation (tetanus)
Produces stronger twitches than low-frequency stimulation
what is elasticity due to primarily? sec or pec
SEC-series elastic component
ST fibers-what type of activity?
ST fibers-great for endurance distance running, cycling, swimming
what does the sarcoplasm contain?
Sarcoplasm of each fiber contains mitochondria, nuclei, and thread like myofibrils that are aligned parallel to one another. The myofibrils contain two types of protein filaments whose arrangement produces the striated pattern after which skeletal, or striated muscle is named
what is active insufficiency?
The point at which a muscle cannot shorten any farther due to contracting. Two-joint muscles can fail to produce force when slack (active insufficiency) Active- condition occurring when a two-joint muscle cannot shorten enough to cause full range of motion at both joints it crosses at the same time Muscles are too relaxed and unable to form a fist
what is eccentric training more beneficial for compared to concentric?
This type of training has been found to be more effective than concentric training in increasing muscle size and strength. As compared with concentric and isometric training, however, eccentric training is also associated with delayed onset muscle soreness
force velocity relationship
When the force is neglible, muscle contracts with maximum velocity. (more force, less velocity. Less force, more velocity)
can exercise change muscle fibers?
Yes, exercise training over time can result in changes in fiber types within an individual.
from a mechanical perspective, the musculotendinius unit behaves as _______ with ______ in parallel with _______ (muscle membranes) and in series with another elastic component (___)
a contractile component muscle fibers elastic component tendons
what does a muscle's viscoelastic property enable the muscle to do? what does viscoelastic mean?
a muscle's viscoelastic property enables it to progressively lengthen over time when stretched Viscoelastic=having the ability to stretch or shorten over time -when you stretch your muscle, it doesn't just recoil super quickly. it takes time, which is called viscoelastic
what is muscle irritability
ability to respond to a stimulus
what is elasticity?
ability to return to normal resting length following a stretch
purpose of series elastic component
acts as a spring to store elastic energy when a tensed muscle is stretched
agonist
acts to cause a movement
neutralizer
acts to eliminate an unwanted action produced by an agonist
antagonist
acts to slow or stop a movement
stabilizer
acts to stabilize a body part against some other force
two factors known to affect muscle fiber types
age and obesity -regular high intensity exercise can reduce the loss of motor units associated with aging
4 roles of a muscle
agonist, antagonist, stabilizier, and neutralizer
what is the ability to develop tension
also known as contraction -the contractile component of muscle function
the same number of fibers present at birth is apparently maintained through life, except for the occasional loss from injury. the increase in muscle size after resistance training thus is generally believed to represent _____
an increase in fiber diameters rather than the number of fibers themselves
more stretch, more
available force for the muscle
three types of muscle contractions
concentric, eccentric, isometric
sarcomere (when is it large vs small)
contractile unit of a muscle fiber -develops depending on the amount of overlap between the actin and myosin -if overlap is large, length of sarcomere is decreased
sarcomere
contractile unit of a muscle fiber. composed of alternating dark and light bands that give muscle its striated appearence
mono-articular muscle
crosses only one joint
physiological cross sectional area
cut the muscle perpendicular to the muscle fibers . pennant or parallel
anatomical cross sectional area
cut the muscle perpendicular to the muscle line or body. along the tendon line (B)
isometric muscle contraction
develops tension without changing length
what is the stretch shortening cycle?
eccentric contraction followed immediately by concentric contraction When an actively tensed muscle is stretched just prior to contraction, the resulting contraction is MORE FORCEFUL than in the ABSENCE of the prestretch
both the SEC and PEC have a viscous property which allows what?
enables a muscle to stretch and recoil in a time dependent fashion
FT fibers can be converted to ST fibers with what type of training? FT IIb can be converted to IIa with _______?
endurance training (FT-->ST) heavy resistance training
type IIB fast twitch-glycolytic (contraction speed, fatigue rate, diameter)
fast fast large
type IIA fast twitch-oxidative glycolytic (contraction speed, fatigue rate, diameter)
fast intermediate intermediate
types of fibers
fast twitch and slow twitch
fast twitch (FT) fibers vs slow twitch fibers
fast-reach peak tension and relax more quickly. slow-takes a lot longer to reach peak tension and takes longer to relax
parallel fiber arrangement
fibers are roughly parallel to the longitudinal axis of the muscle sartorius, biceps brachii
the stronger a muscle, the _____ the magnitude of its isometric maximum on the force-velocity curve
greater
Individuals genetically endowed with a high percentage of FT fibers may gravitate to sports requiring ____, and those with a high percentage of ST fibers may choose _______ sports. However, the fiber type distributions of both elite strength-trained and elite endurance-trained athletes fall within the range of fiber type compositions found in untrained individuals.
high FT fibers-strength high ST-endurance
summation
increased force of contraction by a skeletal muscle fiber when a twitch occurs before the previous twitch relaxes building in an additive fashion. multiple signals and summation can occur and tension is progressively elevated until a maximum value for that fiber is reached
eccentric ____muscle size and strength by _______ the muscle
increases, by lengthening
muscle gets longer, force _______ muscle gets shorter, force _____
increases, decreases
-although all fibers in a motor unit are the same type, most skeletal muscles contain both fast twitch and slow twitch fibers, with the relative amounts varying from muscle to muscle
k
what does a longer PCSA mean?
larger force capability
PCSA are _____ than ACSA in pennant muscle fibers
longer
When an actively tensed muscle is stretched just prior to contraction, the resulting contraction is _____ FORCEFUL than in the ABSENCE of the ______
more forceful prestretch without stretch first, muscle cannot produce as much force
a muscle can perform substantially _____ work when it is actively ______ prior to shortening than when it simply contracts
more, stretched
most large muscles have a _____ type of fiber (fast vs slow twitch)
most large muscles are mixed fiber types
contusions
muscle bruises caused by compressive forces sustained during impacts myositis ossificans
what is tension capability of the muscle tissue affected by? (3)
muscle cross sectional area (anatomical cross sectional area ACSA and physiological crosss sectional area PCSA) training state of muscle and moment arms
eccentric contraction
muscle lengthens as it maintains tension
contractile component
muscle property enabling tension development by stimulated muscle fibers
muscle tension development capability is less following _______
muscle shortening
multi-articular muscle
muscle that crosses three or more joints
amount of maximum isometric tension a muscle is capable of producing is partly dependent on the _______
muscles length
is muscle fiber composition different across genders?
no. it is the same
are all muscle fibers the same length>
no. some fibers run the entire length of a muscle; others are shorter
is it impossible to move a heavy object at a fast speed?
not impossible to move a heavy resistance at a fast speed though. The stronger the muscle is, the greater the magnitude of maximum isometric tension (maximum amount of force that a muscle can generate before actually lengthening as the resistance is increased)
muscle strains
overstretching of muscle tissue hamstrings are the most frequently strained
types of fiber arrangement
parallel and pennate
what are the two major components of elastic behavior of a muscle?
parallel elastic component (PEC) and series elastic component (SEC)
where is the parallel elastic component derived from?
passive elasticity derived from *muscle membranes*
where is the series elastic component derived from?
passive elasticity derived from *tendons* when a tensed muscle is stretched
which type of fiber has higher peak tension?
peak tension is typically greater for fast twitch fibers than slow twitch
two types of muscle architecture
pennant (like a feather) or parallel
what does a longer PCSA mean for the pennant fibers?
pennant fibers are better for force production capacity
examples of stretch-shortening cycle
plyometrics, baseball pitching
movements that are precisely controlled, such as those of the eyes or fingers, are produced by motor units with ____ numbers of fibers. -gross, forceful movements, such as those produced by the gastrocnemius, are usually the result of the activity of ____ motor units
precise movements-small number of fibers gross movements-large motor units, many fibers
single stimulus
present one at a time in random order and the person's reaction to each is recorded
Repetitive stimulation of muscle fibers
produces contractions of longer duration and greater tension than a single twitch
relaxed vs contracted sarcomere
relaxed-large sarcomere contracted-small sarcomere
with warm up, there is a shift to the ______ in the force-velocity curve, with _______ maximum isometric tension and _______ maximum velocity of shortening possible at a given load
right higher higher
what is the membrane surrounding the muscle fiber?
sarcolemma
what is the specialized cytoplasm in the sarcolemma called?
sarcoplasm
pennate fiber arrangement
short fibers attach to one or more tendons within the muscle. like a feather and can be quantified
concentric contraction
shortening of muscle
tension doesn't necessarily mean the muscle is ______
shortening. tension could be stretching the muscle as well
what is a muscle fiber?
single muscle cell
how can muscle fibers grow?
skeletal muscle fibers grow in both length and diameter from birth through adulthood
in single muscle fibers, force generation is at its peak when the muscle is _______
slightly stretched
which type of fibers are always recruited first
slow twitch fibers
which fibers are easier to activate?
slow twitch fibers are easier to activate than fast twitch fibers
what is eccentric training associated with
soreness and structural damage later on
tetanus
state of muscle producing sustained maximal tension resulting from repetitive stimulation
stimuli affecting muscles are either ____ or _____
stimuli affecting muscles are either electrochemical, (action potential from an attached nerve), or mechanical (external blow to a portion of a muscle)
within human body, muscles at rest are under passive tension due to their elastic properties, but tension capabilities increased when muscle is slightly _____
stretched
the myofibril has a ____ appearence
striated/striped gives skeletal muscle its appearence
total tension
sum of the active tension provided by muscle fibers and passive tension provided by the tendons and muscle membranes
purpose of parallel elastic component
supplies resistance when a muscle is passively stretched
when activated by a stimulus, a muscle responds by developing
tension
what factors impact muscular strength?
tension generating capability of the muscle tissue
what is extensibility?
the ability to be stretched or to increase in length
contractility-
the ability to shorten its length
how do we measure muscular strength?
the amount of torque a muscle group can generate at a joint
ACSA and PCSA are the ______ cut for parallel muscle fibers
the same
where does the force length curve come from
the sarcomere
what is the effect of muscle temperature (warm up)?
the speeds of nerve and muscle functions increase
thin filament vs thick filament
thin=actin thick=myosin actin binds to myosin during sliding filament theory
how can muscle fiber diameter be increased?
through resistance training
electromechanical delay
time between the arrival of neural stimulus and tension development by the muscle
what covers myosin binding sites on actin?
tropomyosin calcium reaches the tropomyosin and it is removed to expose the actin binding sites on the myosin head
what factor affects muscular force generation?
velocity
what are moment arms of the muscles crossing the joint affected by? (2)
•distance between muscle attachment to bone and joint center •angle of the muscle's attachment to bone
