Mechanical behavior of Skeletal Muscle.ppt

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1. Mechanical Behavior Mechanical Behavior
of the Skeletal Muscleof the Skeletal Muscle

2. Mechanics of Muscle ContractionMechanics of Muscle Contraction
EMG provides a mechanism for …..
evaluating and comparing neural effects on muscle
the contractile activity of the muscle itself
EMG also helps to study ….
Various aspects of the contractile process, particularly
the time relationship between the onset of electrical
activity in the muscle and actual contraction of muscle
fiber
Mechanics of Muscle ……
The twitch responce
the various ways in which the muscle contracts to move a
joint, control its motion, or maintain its position

3. Summation And Tetanic ContractionSummation And Tetanic Contraction
Muscle twitch ….
“ The mechanical response of a muscle to a single stimulus
of its motor nerve”
the fundamental unit of recordable muscle activity
Latency period ….
“ An interval of a few milliseconds b/w stimulation &
tension production in the muscle fibers”
It represents the time required for the "slack" in elastic
components to be taken up
The contraction time ….
“ The time from the start of tension development to peak
tension”

4. Summation And Tetanic ContractionSummation And Tetanic Contraction
The Relaxation time ….
 “The time from peak tension until the tension drops to
zero”
Some muscle fibers contract with a speed of only 10 m sec;
others may take 100 m sec or longer
An action potential lasts only approx. 1 to 2 m sec. This is
a small fraction of the time taken for the subsequent
mechanical response. Thus it is possible for a series of
action potentials to be initiated before the first twitch is
completed if the activity of the motor axon is maintained.

5. Summation And Tetanic ContractionSummation And Tetanic Contraction
Summation ….
“ When mechanical responses to successive stimuli are
added to an initial response, the result is known as
summation”
Refractory Period ….
“ If a second stimulus occurs during the latency period of
the first muscle twitch, it produces no additional response
and the muscle is said to be completely refractory”
The greater the frequency of stimulation of the muscle
fibers, the greater the tension produced in the muscle as a
whole

6. A)S1 is applied to the muscle, and the
resulting twitch lasts 150-msec
S2 & S3 stimuli are applied to the
muscle after 200-msec intervals when
the muscle has relaxed completely, thus
no summation occurs …. A single
twitch
B) S3 is applied 60 msec after S2 (when the
mechanical response from is beginning
to decrease)
The resulting peak tension…. ?
C) The interval b/w S2 and S3 is further
reduced to 10 msec
The resulting peak tension…. ?
The resulting tension …. a smooth
curve
Summation of Contractions
In a Muscle

7. Summation And Tetanic ContractionSummation And Tetanic Contraction
Tetanic Contraction ….
“ Sustained tension as a result of summation”
In this case, the rapidity of stimulation outstrips the
contraction-relaxation time of the muscle so that little or
no relaxation can occur before the next contraction is
initiated
The repetitive twitching of all recruited motor units of a
muscle is a principal factor responsible for the smooth
movements produced by the skeletal muscles

8. Generation Of Muscle TetanusGeneration Of Muscle Tetanus

9. Muscle ContractionMuscle Contraction
The Muscle Tension ….
“the force exerted by a contracting muscle on the bone
to which it is attached”
The Resistance Or Load ….
“the external force exerted on the muscle”
Moment (torque) ….
“ A turning effect of muscle tension on the involved
joint ”
Moment = the muscle force × the perpendicular
distance b/w its point of application and the center of
motion

10. Classification of Muscle Contractions Classification of Muscle Contractions
& the Resulting muscle work& the Resulting muscle work
According to the relationship b/w muscle tension &
the resistance to be overcome
According to the muscle moment generated and the
resistance to be overcome

11. The tension in a muscle varies with the The tension in a muscle varies with the
type of contractiontype of contraction
Isometric Contractions vs. Concentric Contractions
Eccentric Contraction vs. Isometric Contraction
Tension differences are thought to be due to ….
The varying amounts of supplemental tension in the
tendons
Differences in contraction time
The longer Contraction time ….
Greater cross-bridge formationgreater tension
production (Kroll, 1987)
More tension is transmitted to the series elastic
component as the muscle-tendon unit is stretched
Recruitment of additional motor units

12. Concentric, Isometric & Eccentric Concentric, Isometric & Eccentric
ContractionsContractions
Concentric, isometric & eccentric contractions seldom
occur alone in normal human movement (Komi, 1986)
For Example … the eccentric loading prior to the
concentric contraction that occurs at the ankle from
mid-stance to toe-off during gait
Isokinetic Dynamometer ….
Provide constant velocity of joint motion and max. ext.
resistance throughout the ROM of the involved joint
A method of selective training and measurement

13. Types of Muscle Work and ContractionTypes of Muscle Work and Contraction
Dynamic Work ….
Mechanical work is performed
Joint motion is produced
Concentric Contraction ….
Sufficient Muscles tension production to overcome the
resistance of the body segment
The muscles shorten and cause joint movement
Net resulting moment is in the same direction as the
change in joint angle
Example …. the action of the quadriceps in extending
the knee when ascending stairs

14. Types of Muscle Work and ContractionTypes of Muscle Work and Contraction
Eccentric contraction ….
Muscle cannot develop sufficient tension to overcome
by the external load
Progressively lengthens instead of shortening to
decelerate the motion of a joint
Net resulting moment is in the opposite direction
from the change in joint angle
Example …. the action of the quadriceps when
descending stairs to decelerate flexion of the knee

15. Types of Muscle Work and ContractionTypes of Muscle Work and Contraction
Isokinetic Contraction ….
Movement of the joint is kept at a constant velocity i.e.
the velocity of shortening or lengthening of is constant
No acceleration of the body part & muscle energy is
entirely converted to a resisting moment
The muscle force varies throughout the range of joint
motion (Hislop & Perrine, 1967)
The muscle contracts concentrically and eccentrically
with different directions of joint motion e.g. the flexor
muscles of a joint contract concentrically during flexion
& eccentrically during extension

16. Types of Muscle Work & Types of Muscle Work &
ContractionContraction
Isoinertial contraction ….
When a constant external load is lifted
Moment produced by the muscle vs. the resistance to be
overcome
At the extremes of motion, the inertia of the load must be
overcome and muscle torque is maximal
In the midrange of the motion, with the inertia overcome,
the muscles contract concentrically and the torque is sub-
maximal

17. Types of Muscle Work & ContractionTypes of Muscle Work & Contraction
Isotonic Contraction ….
The tension is constant throughout a range of
joint motion
Isotonic muscle contraction in the truest sense
does not exist in the production of joint motion
(Kroll, 1987)

18. Static Work Static Work
(Isometric Contraction)(Isometric Contraction)
Mechanical Work vs. Physiological
Work during an Isometric
Contraction
Posture or joint position is
maintained
Muscles are not always directly
involved in the production of joint
movements
Isometric Heat Production
An initial isometric phase in all
dynamic contraction

19. Static Work Static Work
(Isometric Contraction)(Isometric Contraction)
A restraining or a holding action, e.g. to maintain the
body in an upright position in opposing the force of
gravity
Example ….
Gripping of an object ….. the joints of the hand do not
move but muscles generate sufficient force to prevent
the object from being dropped

20. Force Production In A MuscleForce Production In A Muscle
•Principle factors in force production …
Length-tension relationship
Load-velocity relationship
Force-time relationship
Muscle temperature
Prestretching
Muscle fatigue

21. Length-tension RelationshipLength-tension Relationship
Force Production in a muscle vs. Muscle Length
Length-tension in a single muscle fiber …..
Max. tension in resting length (2.0-2.25 µm)
Less tension in shorter length
Progressive decrease in tension as the muscle
lengthen beyond its resting length
 Fiber tension changes due to structural alteration
At sarcomere length 3.6 µm …. No active tension
At sarcomere length less …. Tension diminish
sharply

22. Length-tension in a single muscle fiberLength-tension in a single muscle fiber
The variation in
isometric tension
with sarcomere
length in vertebrate
muscle fibers.
J Physiol, 184, 170.

23. Length-tension Relationship ….Length-tension Relationship ….
Length-tension in whole muscle …..
The greater the amount of stretching, the larger the
contribution of the elastic component to the total
tension
Active Components vs. Passive Components
Active Tension vs. Passive Tension in a muscle
The Passive & the Total Tensions …. depends on the
amount of connective tissue in the muscle
Important role in Biarticular Muscles

24. Length-tension in a whole muscleLength-tension in a whole muscle
The curve
demonstrates that
as a muscle is
progres
­sively
stretched beyond
its resting length,
the passive
tension rises and
the active tension
decreases

25. Load-velocity RelationshipLoad-velocity Relationship
The relationship b/w
velocity of muscle
shortening or
lengthening and
different constant loads
The velocity of
shortening of a muscle
is inversely related to the
ext. load applied
(Guyton, 1986)

26. Load-velocity RelationshipLoad-velocity Relationship

Minimal Load …. the muscle
shortens with maximal speed
 Increasing Loads …. the muscle
shortens more slowly
 When the Ext. load equals the
max. muscle force …. No muscle
shortening (zero velocity) and
muscle contracts isometrically
 Ext. load > muscle force
…………. Eccentric contraction
 This lengthening is more
rapid with greater load

27. Force-time RelationshipForce-time Relationship
Contraction time α Muscle
Force production
The force-time curve
Faster contraction leads to lesser
force production
Tension reach to max. .............
10 m sec
Tension to be transferred to the
elastic components ………….
up to 300 m sec

28. Prestretching vs. Muscle WorkPrestretching vs. Muscle Work
Stretch-induced enhancement of work production in
a muscle
 Shortening of a muscle after being stretched
More muscle work production
(Cuillo & Zarins, 1983)
Elastic Energy Storage in series elastic &
contractile components during stretching
A Research Study shows …….
Intrinsic mech. properties of myofibrils are
important in the stretch-induced enhancement of
work production (Takarada et al., 1997)

29. Muscle Temperature vs. Muscle Temperature vs.
Muscle workMuscle work
A Rise in Muscle Temperature causes …..
Increase in conduction velocity across the sarcolemma
Increase in the frequency of stimulation
Production of muscle force (Phillips & Petrofsky,
1983)
Greater Enzymatic activity of muscle metabolism
Increase in Elasticity of the collagen
A Research study shows ……
6 to 34°C rise in muscle temperature results in an
almost linear increase of the tension/stiffness ratio
(Caller et al., 1998)

30. Muscle Temperature vs. Muscle Muscle Temperature vs. Muscle
force productionforce production
Increase in Muscle Temperature due to…..
Increase in blood flow
Production of the heat by metabolism, by the release
of the energy of contraction and by friction of
contractile components
At low temperature (10°C) ……
There is significant inhibition of the max. shortening
velocity & the isometric tension
Caused by decreased pH in the muscle
The pH plays a much less important role at temp.
close to the physiological level (Pate et al., 1995)

31. Effect Of FatigueEffect Of Fatigue
The ability of a muscle to contract and relax is
dependent on the availability ATP
Adequate supply of O2 & nutrients
Sufficient provision of ATP = Low-frequency Twitch
Responses for a Long time
The frequency of twitch responses must be low
Prolonged high frequency stimulation outstrips the
muscle's ability to produce sufficient ATP for
contraction. As a result, tension production declines
and eventually ceases.
Tetanic contractions Muscle Fatigue
A period of rest is important before stimulation is
continued

32. Fatigue in a muscle contracting
Isometrically
(Adapted from Luciano, D.S., Vander, A.J., & Sherman,
J.H. (1978). Human Function and Structure (pp. 113-
136). New York: McGraw-Hill)

33. Effect Of FatigueEffect Of Fatigue
Three sources supply ATP in muscle ….
1.Creatine phosphate
2.Oxidative phosphorylation in the mitochondria
3.Substrate phosphorylation during anaerobic
glycolysis
Myosin ATPase adenosine diphosphate
(ADP) and phosphate (Pi)
Creatine phosphate …. The most rapid means of
ATP production in muscle fiber
Oxidative phosphorylation ….. Moderate rates of
muscle activity

34. Glycolysis Pathways …… Intense Exercises / Activities
Smaller amount of ATP production from large amount
of glucose breakdown with faster rate
Lactic Acid formation as end product
An additional source of rapid supply of ATP to muscle
Quick depletion of muscle’s glycogen in an intense
activity
Fatigue occur in intense activity (rapid break down of
ATPs with slow rate of replacement of ATPs)
Rapid and heavily breathing after strenuous exercise
(muscle returns to its original state)
Effect Of FatigueEffect Of Fatigue

35. Effect Of FatigueEffect Of Fatigue
Muscle returning to normal state ….. Only 20 to 25
% chemical energy is converted to movement by the
muscle
Muscle efficient work …. Only 45 % energy is used
for contraction (Arvidson et al., 1984;Guyton)
Muscle fatigue is first observed by the lack of
coordination of movement and its effect in the
increasing of loads in tissue

36. Effect Of FatigueEffect Of Fatigue
Research studies …….
The skill of the person in performing a given action is
affected by fatigue (Bates et al. 1977)
The fatigue effect on runners. The runners decrease
their knee extension when fatigue occurs (Bates et al.,
1977)
The motion coupling of the spine at exhaustive
extension flexion……. when an individual became
fatigued, the coupled motion increased and therefore the
spinal torque increased (Parnianpour (1988)
The most deleterious component of the neuromuscular
adaptation to the fatigue …….
Reduction in accuracy control and speed of contraction
which may lead to injury to the muscle

37. Skeletal Muscle Architecture vs. Skeletal Muscle Architecture vs.
Contractile PropertiesContractile Properties
Contractile Component the
sarcomere
Two basic architectural
patterns of myofibrils:
More sarcomere in series
Longer myofibril
More sarcomere in parallel
More thick myofibril
1) Muscle force α cross-section of
myofibril ……(Fig. A) (Baratta et al., 1998; Lieber &
Bodine-Fowler, 1993)
A

38. Skeletal Muscle Architecture vs. Skeletal Muscle Architecture vs.
Contractile PropertiesContractile Properties
Muscles with shorter fibers & a
larger cross-sectional
Muscle for force production
e.g. Quadriceps muscle
2) The velocity & excursion of
motor units α the length of the
myofibril …(Fig. B)
Muscles with long fibers &
smaller cross-sectional area
Muscle for
excursion and velocity e.g.
Sartorius muscle
(Baratta et al., 1998; Lieber & Bodine-
Fowler, 1993)
B

39. Muscle Fiber DifferentiationMuscle Fiber Differentiation
Three distinct types of muscle fibers on the basis of
differing contractile and metabolic properties
(Brandstater & Lambert, 1969; Buchtahl & Sohmal-
burch, 1980)
The three fiber types ……
Type I (Slow-twitch Oxidative fibers)
Type IIA (Fast-twitch Oxidative-Glycolytic fibers)
Type IIB (Fast-twitch Glycolytic fibers)

40. Type I
Slow-Twitch
Oxidative
(SO)
Type IIA
Fast-Twitch
Oxidative-Glycolytic
(FOG)
Type IIB
Fast-Twitch
Glycolytic
(FG)
Speed of contraction Slow Fast Fast
Primary source of ATP
Production
Oxidative
phosphorylation
Oxidative
phosphorylation
Anaerobic
glycolysis
Glycolytic enzyme activityLow Intermediate High
Capillaries Many Many Few
Myoglobin content High High Low
Glycogen contents Low Intermediate High
Fiber diameter Small Intermediate Large
Rate of fatigue Slow Intermediate Fast
Properties of Skeletal Muscle fibers

41. Muscle Fiber DifferentiationMuscle Fiber Differentiation
Research studies ………
Burke et al., 1971 …. The nerve innervating the muscle
fiber determines its fiber type. Thus, MFs of each MU
are a single type.
Munsat, McNeal, & Waters, 1976 …. In humans
electrical stimulation was found to change the fiber type
The fiber composition of a given muscle depends on the
function of that muscle for example …. the soleus
muscle, contain a mixture of the three muscle fiber types
Fiber types are genetically determined (Costill et al.,
1976; Gollnick, 1982)

42. Muscle Fiber DifferentiationMuscle Fiber Differentiation
Recruitment Patterns of Motor Units ….
In a typical mixed muscle exerting low
tension, some of the small motor units (type I
fibers) contract. As the frequency becomes
maximal, larger motor units (FOG fibers) and
eventually FG fibers are recruited. As the peak
muscle force decreases, the larger units are
the first to cease activity (Guyton, 1986;
Luciano, Vander, & Sherman, 1978).

43. Muscle Fiber DifferentiationMuscle Fiber Differentiation
Fiber composition in average population ……
Type I muscle fibers …… Approx. 50 to 55%
Type IIA muscle fibers …… Approx. 30 to 35%
Type IIB muscle fibers …… Approx. 15%
Fiber composition in Elite Athletes ……
Sprinters & Shot putters … High % of Type II fibers
Distance Runners & Cross-country Skiers … Higher %
of type I fibers
Endurance Athletes …………… 80% type I fibers
Short & Explosive Efforts …… 30% of these fibers
(Saltin et al., 1977)

44. Muscle InjuriesMuscle Injuries
Muscle injuries ….
Contusion, Laceration, Ruptures, Ischemia,
Compartment Syndromes & Denervation
Muscle Injury ……… weakness of muscles
significant disability
Muscle trauma ……… diminish muscle strength,
limit ROM & lead to Myositis Ossificans
Muscle contractions against resistance ……Muscle
tissue tears
Acute muscle ischemia & compartment syndromes
……… Extensive muscle necrosis
Compartment Syndrome …….. Increased pressure
within a confined muscle compartment

45. Muscle InjuriesMuscle Injuries
•Muscle Remodeling …….
•similar to the bone, articular cartilage and
ligaments repair processes
•Muscle disuse atrophies after immobilization
•Muscle hypertrophies after strength training

46. Effects Of Disuse &Effects Of Disuse &
Immobilization Immobilization
These effects include ……
Loss of endurance & strength
Muscle atrophies
Biochemical changes
These effects are dependent on fiber type and muscle
length during immobilization. Immobilization in a
lengthened position has a less deleterious effect
(Appell, 1997; Kasser, 1996; Ohira et al., 1997;
Sandmann, et al., 1998)
A program of immediate or early motion may prevent
muscle atrophy after injury or surgery (Kannus et al.,
1998a)

47. Effects Of Disuse &Effects Of Disuse &
Immobilization Immobilization
Clinical Findings …..
Isometric exercises to reverse the disuse atrophy of
the quadriceps muscle are not helpful
Dynamic exercises can be beneficial
Type I fibers atrophy with immobilization (Kannus et
al., 1998b)
Intermittent isometric exercise ……. sufficient to
maintain the metabolic capacity of the type II fiber
More continuous impulse for type I fiber
Electric stimulation may prevent the decrease in type
I fiber size and the decline in its oxidative enzyme
activity caused by immobilization (Eriksson et al.,
1981).

48. Effects Of Disuse &Effects Of Disuse &
Immobilization Immobilization
Decrease in the size and aerobic capability of
muscle fibers in elite athletes ………
In endurance athletes ……. type I fibers are
affected
Sprinting ……… type II fibers are affected

49. Effects of physical trainingEffects of physical training
Physical training …increase in muscle bulk & strength
The relative percentage of fiber types composing a
person's muscles may also change with physical
training (Arvidson, Eriksson, & Pitman, 1984)
Increase in muscle cross-sectional area vs. athlet’s
principal activity ….
In endurance athletes, the area of muscle taken up by
type I and type IIA fibers increases at the expense of
the total area of type IIB fibers

50. Effects of physical trainingEffects of physical training
•Stretching Exercise ……….. increases muscle
flexibility, maintains and improve the ROM,
and increases the elasticity and length of the
musculo-tendinous unit (Brobeck, 1979;
Cuillo & Zarins, 1983)
Sustained Stretching
PNF Stretching
Ballistic Stretching

51. Muscle StrainsMuscle Strains
Grade I (Mild Strain) …..
Pain on muscle contraction
Minimum loss of strength
Few muscle fiber torn
Grade II (Moderate Strain) …..
Moderate to severe pain on isometric contraction
Significant muscle weakness & loss of function
Approx. half of fiber torn
Grade III (Severe Strain) …..
Minimum to no pain
Significant loss of function
Complete loss of function