Muscle function, length tension relationship, length tension relationship, muscle tension, force velocity relationship, muscle action, insufficiency, isometrics, isotonic, passive insufficiency.

1. Prepared By:-
Dr. Mumux Mirani
MPT Sports
Asst. Professor
SSAIP

3. Muscle Tension:-
 The most important characteristic of a muscle is its
ability to develop tension and to exert a force on the
bony lever.
 Tension can be either active or passive, and the total
tension that a muscle can develop includes both active
and passive components.

4. Passive Tension:-
 Passive tension refers to tension developed in the parallel
elastic component of the muscle.
 Passive tension in the parallel elastic component is created
by lengthening the muscle beyond the slack length of the
tissues.
 The parallel elastic component may add to the active
tension produced by the muscle when the muscle is
lengthened, or it may become slack and not contribute to
the total tension when the muscle is shortened.
 The total tension that develops during an active
contraction of a muscle is a combination of the passive
(noncontractile) tension added to the active (contractile)
tension

5. Active Tension:-
 Active tension refers to tension developed by the
contractile elements of the muscle.
 Active tension in a muscle is initiated by cross-bridge
formation and movement of the thick and thin
filaments.
 The amount of active tension that a muscle can
generate depends on neural factors and mechanical
properties of the muscle fibers.
 The neural factors that can modulate the amount of
active tension include the frequency, number, and size
of motor units that are firing.

6. Isometric Length-Tension
Relationship
 The direct relationship between isometric tension
development in a muscle fiber and the length of the
sarcomeres in a muscle fiber.
 There is an optimal sarcomere length at which a
muscle fiber is capable of developing maximal
isometric tension.
 Muscle fibers develop maximal isometric tension at
optimal sarcomere length because the thick and thin
filaments are positioned so that the maximum number
of cross-bridges within the sarcomere can be formed.

7. Cont…
 If the muscle fiber is lengthened or shortened beyond
optimal length, the amount of active tension that the
muscle fiber is able to generate when stimulated
decreases.
 When a muscle fiber is lengthened beyond optimal
length, there is less overlap between the thick and thin
filaments and consequently fewer possibilities for
crossbridge formation.
 However, the passive elastic tension in the parallel
component may be increased when the muscle is
elongated.

9. Cont…
 A similar loss of isometric tension or diminished
capacity for developing tension occurs when a muscle
fiber is shortened from its optimal sarcomere length.
 When the sarcomere is at shorter lengths, the distance
between the Z disks decreases and there is
interdigitation of the filaments.
 The interdigitation of the thick and thin filaments
may interfere with the formation of cross-bridges from
the myosin molecules, thus decreasing the active force.

10. Cont…
 Sarcomere length obviously changes during dynamic
contractions (concentric and eccentric contractions)
that affect the tension that can be developed in the
muscle.
 However, during dynamic contractions, the length-
tension relationship must be combined with the force-
velocity relationship to determine the effect that both
length and velocity have on the muscle tension.

11. Application of the L-T relationship
 when the muscle is acting at a joint, the torque
produced is not only a function of the muscle force
(which depends on muscle length) but also a function
of the MA of the muscle.
 This means that at a certain joint angle, the muscle
length may be short (which suggests that force will be
low), but the MA may be relatively long, thus
maintaining a higher joint torque.

12. Cont…
 application of the sarcomere lengthtension relationship is
the observation that a muscle has the diminished ability to
produce or maintain isometric tension at the extremes of
joint motion.
 This probably occurs only in muscles that cross more than
one joint (two-joint or multijoint muscles), in which
muscle length excursion is greater than in singlejoint
muscles.
 A decrease in the torque produced by the muscle may be
encountered when the full ROM is attempted
simultaneously at all joints crossed by a multijoint muscle.

13. Cont…
 This decrease in torque is often referred to as “active
insufficiency.” Although the decrease in isometric
torque can be conveniently explained by the length
changes in the muscle that result in decreased muscle
force, other factors such as the change in MA and the
passive restraint of the lengthened antagonists also
play a substantial role.
 Sarcomere length appears to stay close to the optimal
length during joint movements; therefore, influence of
the MA and passive restraint of the antagonists may be
more important than once thought.

14. Force-Velocity Relationship:-
 The force-velocity relationship describes the relationship
between the velocity of the muscle contraction and the force
produced, therefore providing an explanation for what happens
during concentric and eccentric muscle contractions.
 the force-velocity relationship states that the velocity of muscle
contraction is a function of the load being lifted.
 concentric muscle contraction, as the shortening speed
decreases, the tension in the muscle increases.
 In an isometric contraction, the speed of shortening is zero, and
tension is greater than in a concentric contraction.
 In an eccentric contraction, as the speed of lengthening
increases, the tension in the muscle increases.

16. Cont…
 During dynamic contractions, the length-tension
relationship must be combined with the force-velocity
relationship because both sarcomere length and
velocity of contraction affect the development of
muscle tension.
 At high shortening velocities, the muscle tension will
be low, regardless of sarcomere length.
 The fact that most human movements do not occur at
a constant velocity of contraction complicates the
situation further because the force will vary with
changing velocity and changing length.

17. Types of Muscle Action:-
 Muscle actions (or contractions) are described as
isometric contraction (constant length) or dynamic
contractions consisting of concentric contraction
(shortening of the muscle under load) and eccentric
contraction.
 isometric, concentric, and eccentric muscle
contractions were introduced in relation to the
movement occurring at the sarcomere level.

18. Cont…
 When a muscle fiber is activated so that cross-bridges
form, the sarcomeres in the fiber will either stay at
constant length, shorten, or lengthen, depending on
the load that is applied.
 An isometric contraction occurs when the muscle is
activated and the sarcomere does not change length; a
concentric contraction occurs when the sarcomere
shortens; and an eccentric contraction occurs when
the sarcomere lengthens (the load is greater than the
force of the sarcomere).

19. Cont…
 When the whole muscle is activated and the bones
that it is attached to do not move, it is called an
isometric contraction.
 Holding the weight without changing the joint angle
means that the muscle is contracting isometrically.
 During an isometric contraction, no work is being
done because the joint is not moving.
 ]The formula for work is W = F d, where W is work, F
is the force created by the muscle, and d is the distance
that the object, in this case the joint, is moved.

20. Cont…
 During a concentric contraction, the bones move closer
together as the whole muscle shortens.
 Positive work is being done by the muscle because the joint
moves through a ROM.
 During an eccentric contraction, the bones move away
from each other as the muscle tries to control the descent
of the weight.
 The muscle lengthens as the joint moves through the
ROM.
 The work that is being done during an eccentric
contraction is called negative work because the work is
done on the muscle rather than by the muscle.

21. Cont…
 The amount of tension that can be developed in a muscle
varies according to the type of contraction as was seen in
the force-velocity relationship.
 A greater amount of tension can be developed in an
isometric contraction than in a concentric contraction.
 the tension developed in an eccentric contraction is
greater than what can be developed in an isometric or
concentric contraction.
 greater tension development in a muscle during an
eccentric contraction than in a concentric contraction may
be due, in part, to either mechanical factors in the
attachment and detachment of crossbridges or to
alterations in the neural activation of the muscle.

22. Cont…
 Many times during normal functional activities , the
proximal segment moves and the distal segment is
stationary…
 Sometimes this is referred as “ Reverse Action ” of the
muscle…
 Muscle actions are depended upon its desired motion,
the effects of external forces and the ability to stabilize
other joints…

26. Production of Torque:-
 As clinicians, we often assess the patient’s muscle strength.
 Whether we assess the strength by using an instrument
(such as an isokinetic device) or by simple manual
pressure, we are actually determining the amount of joint
torque that the muscle can produce.
 In many physiological experiments on muscle, the muscle
is isolated from the bone and the actual muscle force is
measured as the muscle is activated.
 When the muscle is attached to bones in the body, the
muscle still produces a force, but it now acts over a MA at
the joint to produce a torque.

27. Cont…
 The MA of the muscle can change with joint position,
thus affecting the torque being produced.
 For example, if the biceps brachii is activated to
produce 10 pounds of force with a small MA at one
joint position, the torque (muscle strength measured)
will be less than if the MA of the muscle were larger at
a different joint position.

29. Interaction of Muscle & Tendon:-
 The interaction between muscle and tendon
(including the aponeurosis) during muscle contraction
and movement has some important functional
implications.
 For example, during an isometric contraction , the
muscle actually shortens slightly and the tendon
lengthens slightly.
 In many muscles, the fibers may shorten and the
tendon may lengthen by as much as 10% of their
resting length during an isometric contraction.

30. Cont…
 The compliance of the tendon (or ability to lengthen under
load) is important in augmenting the torque production of the
muscle.
 This is the basis for plyometric exercises, in which the
muscle/tendon complex is stretched before a forceful concentric
contraction.
 The stretch immediately before the concentric contraction helps
produce a much greater torque during the concentric
contraction.
 Although the exact mechanism for the increase in torque is
debated, evidence shows that the muscle fibers tend to stay at
constant length (isometric) while the tendon lengthens, storing
energy to be used during the concentric contraction.

31. Classification of Muscles:-
 Individual muscles may be named in many different ways. Such
as according to ,
 Shape (rhomboids, deltoid),
 number of heads (biceps, triceps, quadriceps),
 location (biceps femoris, tibialis anterior),
 or a combination of location and function (extensor digitorum
longus, flexor pollicis brevis).
 Groups of muscles are categorized on the basis of either the
actions they perform or the particular role they serve during
specific actions.
 When muscles are categorized on the basis of action, muscles
that cause flexion at a joint are categorized as flexors.
 Muscles that cause either extension or rotation are referred to as
extensors or rotators, respectively.

32. Cont…
 When muscles are categorized according to role,
individual muscles or groups of muscles are described
in terms that demonstrate the specific role that the
muscle plays during action.
 When using this type of role designation, it matters
not what action is being performed (flexion,
extension) but only what role the muscle plays.

33. Based on Role of the Muscle in
Movement
 The term prime mover (agonist) is used to designate a
muscle whose role is to produce a desired motion at a
joint.
 If flexion is the desired action, the flexor muscles are
the prime movers and the muscles (extensors) that are
directly opposite to the desired motion are called the
antagonists.
 The desired motion is not opposed by the antagonists,
but these muscles have the potential to oppose the
action.

34. Cont…
 however, the agonist and the potential antagonist contract
simultaneously, then cocontraction occurs Co-contraction
of muscles around a joint can help to provide stability for
the joint and represents a form of synergy that may be
necessary in certain situations.
 Co-contraction of muscles with opposing functions can be
undesirable when a desired motion is prevented by
involuntary co-contraction, such as occurs in disorders
affecting the control of muscle function (e.g., cerebral
palsy).
 Muscles that help the agonist to perform a desired action
are called synergists.

36. Based on Muscle Architecture
 Placing muscles into functional categories such as flexor and extensor
or agonists and antagonists helps to simplify the task of describing the
many different muscles and of explaining their actions.
 However, muscles can change roles. A potential antagonist in one
instance may be a synergist in another situation.
 An example of this can be found in the preceding discussion. The
extensors and flexors on the ulnar side of the wrist are antagonists
during the motion of radial deviation, but during ulnar deviation, these
same muscles are synergists.
 Despite this apparent change in role, muscles that have similar
functions also have similar architectural characteristics.
 This may seem obvious, because muscle architecture plays such an
important role in determining the potential force and velocity of
muscle contraction

38. Based on Length of the Moment
Arm
 The orientation of the muscle to the joint has also been used to
classify muscles into groups.
 The length of the muscle MA is an important component of
determining the joint torque and, in combination with the fiber
length, the ROM through which the muscle can move the joint.
 The ratio of the fiber length to the MA provides a way of
identifying which factor plays a greater role in the production of
the joint torque and in determining the resulting ROM at the
joint.
 For example, the ratio of fiber length to MA is much higher in
the wrist extensor muscles than in the wrist flexor muscles,
which suggests that fiber length plays a greater role than does
MA in the wrist extensors than in the wrist flexors.

39. Factors Affecting Muscle Function:-
 Types of joints and location of muscle attachments.
 Number of joints crossed by the muscle.
 Passive insufficiency.
 Sensory receptors.

40. Types of joints and location of
muscle attachments:-
 The type of joint affects the function of a muscle in that the
structure of the joint determines the type of motion that
will occur (flexion and extension) and the ROM.
 The muscle’s location or line of action relative to the joint
determines which motion the muscle will perform.
 In general, muscles that cross the anterior aspect of the
joints of the upper extremities, trunk, and hip are flexors,
whereas the muscles located on the posterior aspect of
these joints are extensors.
 Muscles located laterally and medially serve as abductors
and adductors, respectively, and may also serve as rotators.

41. Cont…
 A muscle’s relative contribution to stability will change
throughout a motion as the rotatory and compressive
components of the muscle’s force vary indirectly with each
other. A muscle provides maximum joint stabilization at
the point at which its compressive component is greatest.
 Disturbances of the normal ratio of agonist-antagonist
pairs may create a muscle imbalance at the joint and may
place the joint at risk for injury.
 Agonist-antagonist strength ratios for normal joints are
often used as a basis for establishing treatment goals after
an injury to a joint.

43. Number of joints crossed by the
muscle:-
 Many functional movements require the coordinated
movement of several joints controlled by a combination of
muscles that cross one or many of the joints.
 The number of joints that the muscle crosses determines
the muscle function. Single-joint muscles tend to be
recruited to produce force and work, primarily in
concentric and isometric contractions.
 Multijoint muscles, in contrast, tend to be recruited to
control the fine regulation of torque during dynamic
movements involving eccentric more than concentric
muscle actions.

44. Cont…
 Multijoint muscles tend to be recruited during more
complex motions requiring movement around
multiple axes.
 If a single-joint motion is desired, a single-joint muscle
is recruited because recruitment of a multijoint
muscle may require the use of additional muscles to
prevent motion from occurring at the other joint or
joints crossed by the multijoint muscles.
 Single-joint and multijoint muscles may also work
together in such a way that the single-joint muscle can
assist in the movement of joints that it does not cross.

46. Passive insufficiency:-
 If a person’s elbow is placed on the table with the forearm
in a vertical position and the hand is allowed to drop
forward into wrist flexion, the fingers tend to extend.
 Extension of the fingers is a result of the insufficient length
of the finger extensors that are being stretched over the
flexed wrist.
 The insufficient length is termed Passive insufficiency. If
the person moves his or her wrist backward into wrist
extension, the fingers will tend to flex.
 Flexion of the fingers is a result of insufficient length of the
finger flexors as they are stretched over the extended wrist.

47. Cont…
 One-joint muscles rarely, if ever, are of insufficient length
to allow full ROM at the joint.
 Two-joint or multijoint muscles, however, frequently are of
insufficient length or extensibility to permit a full ROM to
be produced simultaneously at all joints crossed by these
muscles.
 The passive tension developed in these stretched muscles is
sufficient to either check further motion of the bony lever
(passive resistance torque / torque of the effort force) or, if
one segment of the joint is not fixed, may actually pull the
bony lever in the direction of the passive muscle pull.

50. Sensory receptors:-
 Two important sensory receptors, the Golgi tendon
organ and the muscle spindle, affect muscle function.
 The Golgi tendon organs, which are located in the
tendon at the myotendinous junction, are sensitive to
tension and may be activated either by an active
muscle contraction or by an excessive passive stretch of
the muscle.
 When the Golgi tendon organs are excited, they send a
message to the nervous system to inhibit the muscle in
whose tendon the receptor lies.