ithin the fi eld of physiology, there are a number of fundamental principles. Some of these key principles are (a) homeostasis, (b) the linkage between gene expression and physiology, and (c) structure–function relationships. It is this latter principle that forms the foundation of the current chapter. The concept of structure–function relationships extends across the organism-to-molecule spectrum. At the organism level, one can think about a number of examples. For instance, the structural relationship between the glenoid fossa and the head of the humerus gives the shoulder six degrees of motion—a motion that is uncommon among other joints. At the molecular level, one can think about the structure of myosin heavy chains (MHCs) and how this translates into certain functional properties like the force–velocity relationship. The discipline of exercise physiology really represents a subdiscipline or an extension of the fi eld of physiology; and, as such, the fundamental principles are essentially the same except that they are examined typically under conditions where physical activity has been altered. In this context, a great deal of interest has been given to understanding the effects of both activity and inactivity on the structural and functional properties of skeletal muscle during the past 30 to 35 years. Of any cell/tissue type, skeletal muscle certainly exhibits some of the clearest structure–function relationships. Given this perspective, one of the key objectives of this chapter is to provide a backdrop for some of the more detailed discussions that follow in successive chapters. The current chapter is organized into three distinct sections. The fi rst section provides an overview of some of the key structural properties of skeletal muscle (macroscopic to molecular anatomy). The second part of the chapter addresses the linkage between structure and function and the topic of skeletal muscle plasticity as infl uenced by altered physical activity. The fi nal section of this chapter examines issues of muscle plasticity from a comparative perspective and introduces the concept of symmorphosis, a concept related to the optimality of design

1. Concept of Muscle Contraction,
Closed Vs Open Kinetic Chain Exercises
MODERATOR:
• Dr Sandeep Kumar Gupt
Assisstant prof
DEPT OF PMR
KGMU
PRESENTED BY:
• Dr Joe Antony
JR1
DEPT OF PMR
KGMU
1

2. Contents
• Muscle Microanatomy
• Molecular characteristics of myofibril
• Physiology of muscle contraction
• Muscle fiber types
• Factors affecting muscle strength and performance
• Types of muscle contraction
• Effects of exercise training
• Progressive resistance exercise
• Effects of ageing
• Open chain exercises
• Closed chain exercises
2

3. Muscle Microanatomy
• Each skeletal muscle is made of
many muscle fibers, which range in
diameter between 10 and 80 μm.
• Each muscle fiber contains
hundreds to thousands of
myofibrils.
• Each myofibril comprises
approximately 1500 myosin (thick)
filaments and 3000 actin (thin)
filaments, which are responsible
for muscle contraction
Braddom 6th edition 3

4. • Myosin and actin filaments partially
interdigitate, causing myofibrils to
have alternate light and dark bands.
• The light bands contain only actin
filaments and are called I bands
(because they are isotropic to
polarized light).
• Dark bands contain myosin as well as
ends of actin filaments where they
overlap myosin, and are called A
bands (anisotropic to polarized light)
Braddom 6th edition 4

5. • The ends of actin filaments are
attached to Z disks.
• From Z disk, actin filaments
extend in either direction,
interdigitating with myosin
filaments.
• The Z disk passes from myofibril
to myofibril, attaching myofibrils
across muscle fiber.
• Thus entire muscle fiber has
light and dark bands, as do
individual myofibrils, and thus
striated appearance of muscle
fib
Braddom 6th edition 5

6. • The portion of a myofibril or whole muscle fiber between two Z disks
is called a sarcomere.
• The myofibrils within muscle fibers are suspended in a matrix called
sarcoplasm.
• The sarcoplasm contains potassium, magnesium, phosphate,
enzymes, and mitochondria.
• The sarcoplasm also contains sarcoplasmic reticulum, an extensive
endoplasmic reticulum important in control of muscle contraction.
Braddom 6th edition 6

7. Molecular Characteristics of Contractile
Filaments
• Each myosin filament is composed of
200 or more myosin molecules.
• Each myosin molecule is composed of
six polypeptide chains: two heavy
chains and four light chains.
• The two heavy chains are wrapped
around each other to form a double
helix, tail and arm of myosin molecule.
• One end of each of chains is folded
into a globular mass called myosin
head.
• Therefore two myosin heads are lying
side by side.
• The four light chains are also parts of
myosin heads, two to each head
Braddom 6th edition 7

8. • The tails of myosin molecules are bonded together, forming body of
myosin filament.
• Protruding from body, arm and heads of myosin molecules are called
crossbridges, which are flexible at two points called hinges.
• In addition to serving as a component of cross-bridge, myosin head
also functions as adenosine triphosphatase (ATPase), allowing head to
cleave ATP and energize contraction
Braddom 6th edition,Guyton and Hall 12th edition 8

9. Physiology of muscle
contraction
• A motor unit is made up of a motor neuron and all of
the skeletal muscle fibers innervated by the neuron's
axon terminals, including the neuromuscular junctions
between the neuron and the fibres.
• muscle contraction is initiated by release of
acetylcholine from motor nerve.
• Acetylcholine opens protein channels in muscle fiber
membrane, allowing sodium to flow into muscle fiber
membrane and initiating a muscle action potential.
• action potential depolarizes muscle fiber membrane,
causing sarcoplasmic reticulum to release calcium.
• Calcium, in turn, generates attraction between actin
and myosin crossbridges, causing them to slide
together.
Braddom 6th edition 9

10. Sliding filament mechanism
• In relaxed state ends of actin
filaments, derived from two
successive Z disks, barely overlap
each other while at same time
completely overlapping myosin
filaments.
• In contracted state actin
filaments overlap each other to
a great extent, and Z disks are
pulled up to end of myosin
filaments
Braddom 6th edition 10

11. • Actin filaments are composed of
three protein components: actin,
tropomyosin, and troponin.
• Several G-actin molecules form
strands of F-actin. Two F-actin
strands are then wound in a
double helix.
• One molecule of ADP is attached
to each G-actin molecule.
• These ADP molecules represent
active sites of actin filaments
with which myosin cross-bridges
interact to cause muscle
contraction
Braddom 6th edition, Guyton and hall 12 th edition 11

12. • Tropomyosin molecules are wrapped
around F-actin helix. In resting state,
tropomyosin covers active sites of
actin strands, preventing
contraction.
• Attached near one end of each
tropomyosin molecule is a troponin
molecule.
• Each troponin molecule consists of
three protein subunits. Troponin I
has a strong affinity for actin,
troponin T for tropomyosin, and
troponin C for calcium
Braddom 6th edition 12

13. • In resting state troponin-tropomyosin complex is thought to cover
active sites of actin, inhibiting contraction.
• In presence of calcium, this inhibitory effect is removed, allowing
contraction to proceed.
Braddom 6th edition 13

14. Muscle fibre types
Type 1 fiber
• slow oxidative
• best suited for endurance
activities requiring aerobic
metabolism.
Type 2 fiber
• fast twitch
• most active during activities
requiring strength and speed.
• 2A (fast, oxidative glycolytic)
• a type of hybrid that retains some
oxidative capacity.
• 2B (fast glycolytic)
Braddom 6th edition 14

15. Braddom 6th edition 15

16. During anaerobic activity,
• slow oxidative fibers (type 1) are used almost exclusively at intensities
below 70% of ˙VO2max.
• Beyond this intensity, anaerobic pathways are stimulated.
• At ˙VO2max, both type 1 and type 2 are relied on, and oxygen debt
eventually occurs secondary to aerobic metabolism
Braddom 6th edition 16

17. During isometric contractions,
• type 2 fibers are generally recruited when force exceeds 20% of
maximal voluntary contraction.
• If sustained for long periods, however, type 2 can be recruited at
thresholds below 20% of maximal voluntary contraction.
Braddom 6th edition 17

18. Muscle fibre
orientation
• Parallel muscles have their fibers
arranged parallel to length of muscle
and produce a greater range of
motion than similarsized muscles
with pennate arrangement.
• Pennate muscles have shorter fibers
that are arranged obliquely to their
tendons (similar to makeup of a
feather), increasing cross-sectional
area and power produced.
Braddom 6th edition 18

19. Factors affecting muscle strength and
perfomance
• Cross sectional area
• The ability of a muscle to produce force is directly proportional to its cross-
sectional area.
• For parallel muscles, this corresponds to cross-section at bulkiest part of
muscle.
• For pennate muscles, multiple cross-sections are taken at right angles to each
of muscle fibers.
• Pennate muscles are particularly adapted to force production because many
more muscle fibers are contained in pennate muscles and these fibers are
shorter
Braddom 6th edition 19

20. • Length-Tension Relationship
• Maximum force of contraction occurs when a muscle is at its normal resting
muscle length.
• For muscles, this corresponds to about midrange of joint motion or slightly
longer, and is length at which tension just begins to exceed zero.
• If a muscle is stretched beyond resting length before contraction, resting
tension develops, and active tension (the increase in tension during
contraction) decreases.
• Efficiency (percentage of energy that is converted into work instead of heat)
occurs at a velocity of contraction of approximately 30% of maximal.
Braddom 6th edition 20

21. • Torque-Velocity Relationship
• The greatest amount of force is generated by a muscle during fast eccentric
(lengthening) contractions.
• The least amount of force is produced during fast concentric (shortening)
contractions.
• The amount of force developed in order of most force to least force can be
summarized as follows: fast eccentric, isometric, slow concentric, and fast
concentric
Braddom 6th edition 21

22. Types of muscle
contraction
• Isometric contractions -
contractions in which there is no
change in length of muscle.
• No joint or limb motion occurs.
• internal force does not overcome
external force – Exertion against
immovable objects or by holding
joint in a static position
• characteristics of isotonic
contraction depend on the load
against which muscle contracts, as
well as inertia of load
Braddom 6th edition 22

23. • Isotonic contractions occur
when muscle changes length,
producing limb motion
• Concentric contractions occur
when muscle shortens.
• Eccentric contractions occur when
muscle lengthens. More fast
twitch fibers are recruited during
eccentric contractions.
Braddom 6th edition, Board review 3 rd edition 23

24. • Isokinetic contractions -occur when muscle contraction is performed
at a constant velocity.
• This can be done only with assistance of a preset rate-limiting device.
• This type of exercise does not exist in nature.
Braddom 6th edition 24

25. Effects of exercise training
• The SAID principle (specific adaptations to imposed demands) states that a
muscle will adapt to a specific demand imposed on it, making it better able
to handle greater load.
• Neural Adaptations
• Observed strength gains within first few weeks of a weightlifting program
are mostly because of neuromuscular adaptations.
• The nervous system recruits larger motor units with higher frequencies of
stimulation to provide force necessary to overcome imposed resistance.
• Early strength gains and increased muscle tension production from training
therefore result from a more efficient neural recruitment process.
• This means that most of improvement in strength-related functional
activities gained on inpatient rehabilitation units is attributable to neural
recruitment rather than muscle hypertrophy, as a result of relatively short
length of stays
Braddom 6th edition 25

26. Muscle Hypertrophy
• Enlargement of total muscle mass and cross-sectional area.
• Muscle hypertrophy is more common in fast-twitch than in slow-
twitch muscles.
• Type 2A fibers exhibit greatest growth, more so than type 2B and type
1 fibers.
• Muscle hypertrophy is typically experienced after 6 to 7 weeks of
resistance training.
• Conversely, muscle atrophy resulting from disuse occurs primarily in
type 2 fibers
Braddom 6th edition 26

27. • Virtually all muscle hypertrophy occurs from hypertrophy of individual
muscle fibers.
• During muscle hypertrophy rate of muscle contractile protein
synthesis is greater than decay, leading to greater numbers of actin
and myosin filaments in myofibrils.
• The myofibrils within each muscle fiber split, resulting in more
myofibrils in each muscle fiber.
• Only under very rare conditions of extreme muscle force generation
do numbers of muscle fibers increase (fiber hyperplasia), and even
then by only a few percent.
Braddom 6th edition 27

28. • When muscles are stretched to a greater-than-normal length, causing
new sarcomeres to be added at ends of muscle fibers where they
attach to tendons.
• Conversely, when a muscle remains shortened at less than its resting
length, sarcomeres at end of muscle fibers disappear
Braddom 6th edition 28

29. Progressive resistance exercise
• Delorme
• three sets are performed for each exercise.
• Ten repetitions are performed in each set.
• The weight for the first set is 50% of the 10-RM; the second set, 75% of the
10-RM; and the third set, 100% of the 10-RM.
• This is usually referred to clinically as progressive resistive exercise.
Braddom 6th edition 29

30. • Oxford
• individual starts with 10 repetitions at 100% of the 10-RM,
• then 10 repetitions at 75% of the 10-RM,
• then a third set of 10 repetitions at 50% of the 10-RM.
• This is usually referred to in the clinical setting as regressive resistive exercise.
30

31. DAPRE (Daily Adjusted Progressive Resistence Exercise)
• The 1st set in DAPRE involves 10 repetitions at 50% of the athlete’s
predetermined 6-RM.
• The 2nd set consists of six repetitions at 75% of the athlete’s 6-RM.
• The 3rd set consists of as many repetitions as can be performed at the
athlete’s 6-RM.
• The number of repetitions performed in the third set determines the
resistance for the fourth set.
• If 5-7 repetitions were performed in the third set, resistance stays the same.
• If fewer than 5 repetitions were performed in the third set, the weight is lowered by
5 lb.
• If more than 7 repetitions are performed in the third set, the weight is raised by 5 lb.
• 4th set consists of as many repetitions as can be performed to fatigue
• working weight for the next day is established based on the athlete’s
performance during the 4th set
31

32. Effects of Aging
• Although it was previously believed that strength training in older
adults was attributable only to learning or neural factors, reports have
also demonstrated that muscles of older individuals can demonstrate
hypertrophy after strength training
32

33. Open-Chain Exercises
• Involve motions in which distal segment (hand or
foot) is free to move in space, without necessarily
causing simultaneous motions at adjacent joints
• Limb movement only occurs distal to moving joint.
Muscle activation occurs in muscles that cross
moving joint.
• For example, during knee flexion in an open-chain
exercise action of hamstrings is independent of
recruitment of other hip or ankle musculature.
• Open-chain exercises also are typically performed
in non-weight-bearing positions.
• In addition, during resistance training, exercise
load (resistance) is applied to moving distal
segment. 33

34. 34

35. Closed-chain exercises
• involve motions in which body moves on a distal segment
that is fixed or stabilized on a support surface.
• Movement at one joint causes simultaneous motions at
distal as well as proximal joints in a relatively predictable
manner.
• For example, when a patient is performing a bilateral
short-arc squatting motion (mini-squat) and then
returning to an erect position, as knees flex and extend,
hips and ankles move in a predictable pattern along with
knees.
• Closed-chain exercises are primarily performed in weight-
bearing positions
Bilateral closed-chain resisted hip and knee extension.
35

36. Examples in upper extremities
include balance activities in
quadruped, sitting press-ups,
wall push-offs, or prone push-
ups; examples in lower
extremities include lunges,
squats, step- up or step-down
exercises, or heel rises
36

37. CHARACTERISTICS OF OPEN & CLOSED CHAIN
EXERCISES
37

38. Rationale for Use of Open-Chain and Closed-Chain
Exercises
• Rationale is based on goals of an individualized rehabilitation program
and a critical analysis of potential benefits and limitations inherent in
either form of exercise.
• Functional activities involve many combinations and considerable
variations of open- and closed-chain motions
• So, inclusion and integration of task-specific open-chain and closed-
chain exercises into a rehabilitation or conditioning program is both
appropriate and prudent.
38

39. Rationale of Open-Chain Training
• Because open-chain training typically is performed in nonweight-bearing
postures, it may be only option when weight bearing is contraindicated or
must be significantly restricted or when unloading in a closed-chain position
is not possible.
• Soft tissue pain and swelling or restricted motion of any segment of chain
may also necessitate use of open-chain exercises at adjacent joints.
• Any activity that involves open-chain motions can easily be replicated with
open-chain exercises, first by developing isolated control and strength of
weak musculature and then by combining motions to simulate functional
patterns.
39

40. • After a fracture of tibia, for example, lower extremity usually is
immobilized in a long leg cast, and weight bearing is restricted for
at least a few weeks.
• During this period, hip strengthening exercises in an open chain
manner can still be initiated and gradually progressed until partial
weight bearing and closed-chain activities are permissible.
40

41. Closed-Chain Exercises and Weight-Bearing
Restrictions
• While partial weight bearing on involved extremity. This is simple to
achieve in upper extremity; but in lower extremity, because patient is
in an upright position during closed-chain exercises, axial loading in
one or both lower extremities must be reduced
41

42. Parameters and Progression of Closed-
Chain Exercises
42

43. Thank you
• References
• Braddoms 6th edition
• Guyton and hall 12 th edition
• ACSM’s exercise physiology
• Board review of physical medicine and rehabilitation
43