Download Human Movement Systems: Muscular System

Human Movement Systems:
Muscular System
Introduction
In this lesson you will learn about:
• The Muscular System
• Types of muscle tissue
• Skeletal muscle structure
• Muscle contraction
• Skeletal Muscle fiber types
• Principles of force generation
• Muscle soreness
The Muscular System
 Muscles generate
internal tension that,
under the control of the
nervous system,
manipulates the bones
of our body to produce
movement.
Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins
Muscular System
 Three types of muscle tissue:
– Skeletal
• Attaches to the skeleton via tendons, contracts to move
bones
• Voluntary
• Striated appearance
– Smooth
• Found on the walls of hollow organs and tubes (e.g.,
stomach and blood vessels)
• Involuntary
• Smooth appearance
– Cardiac
• Forms the walls of the heart
• Involuntary (controlled by autonomic Nervous system)
• Smooth appearance and intercalated discs
Structure of Skeletal Muscle
 Muscle is the compilation of many individual muscle
fibers neatly wrapped together with connective tissue to
form bundles:
 Each layer of connective tissue extends the length of the
muscle, helping to form the tendon.
– Fascia: Outer-most layer of connective tissue surrounding the
entire muscle.
– Epimysium: Layer of connective tissue under fascia immediately
surrounding the muscle.
– Perimysium: Surrounds bundle of muscle fibers called fascicles.
– Endomysium: Surrounds each muscle fiber (individual muscle
cells)
Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins
Muscle Fibers
 Contain typical cell
components:
•
Cellular plasma called
sarcoplasm (contains
glycogen, fats, minerals,
and oxygen-binding
myoglobin)
•
Nuclei
•
Mitochondria (transform
energy from food into
energy for the cell)
 Unlike typical cells, they also
have structures called
myofibrils.
Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins
Contractile Elements
 Sarcomere: The
contractile unit of the
muscle.
 Myofibrils: actual
contractile components of
muscle tissue:
– Actin: thin filaments
– Myosin: thick filaments
 Lines and bands define
parts of sarcomere:
– Sarcomere is defined as Z-line to
Z-line.
Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins
Muscle contraction
 Muscle contraction
– A contraction occurs when an
electronic impulse is transmitted
from the brain to the muscle.
– Muscle contraction is the result of
the interaction of the actin and
myosin filaments, which causes a
shortening of the individual
sarcomeres, and therefore, a
shortening of their associated
muscle fibers.
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Neuromuscular anatomy
 Motor unit
– A motor nerve and all its associated muscle fibers
– All fibers comprising a motor unit are homogeneous (they are
either all fast-twitch or all slow-twitch).
– Motor units made up of 5–10 fibers are responsible for fine,
delicate movements such as blinking the eye.
– Motor units made up of thousands of fibers are responsible for
forceful movements such as jumping.
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Motor Unit Recruitment Patterns
 All-or-none principle: Motor units give an all-or-none
response
 Size principle: The order of motor unit recruitment is
directly related to the motor neuron size
 Principle of orderly recruitment: Motor units are
activated on the basis of a fixed order
– type I → type IIa → type IIx
 Asynchronic vs Synchronic: Synchronizing more
motor units and thus more muscle fibers produces
more force
Sliding Filament Model
The process of how the
contraction of the
filaments within the
sarcomere takes
place:
 A sarcomere shortens as
a result of the Z lines
moving closer together.
 The Z lines converge as
the result of myosin
heads attaching to the
actin filament and
asynchronously pulling
(power strokes) the actin
filament across the
myosin.
Skeletal Muscle Fiber Types
 Type I: Slow Twitch
–
–
–
–
Higher in capillaries, mitochondria, and myoglobin
Increased oxygen delivery and slow to fatigue
Smaller motor units and fiber size tend to produce less force
Tend to increase capillaries, mitochondria and myoglobin rather
than hypertrophy of fibers.
– Long-term contractions (utilized primarily for posture &
stabilization)
 Type IIx: Fast Twitch
– Lower in capillaries, mitochondria, and myoglobin
– Decreased oxygen delivery and quick to fatigue
– Larger motor units & fiber size tend to produce more force:
Contain more myosin cross-bridges per cross-sectional area of
fiber and produce 10–20% more force than slow-twitch muscle
fibers
– Tend to hypertrophy more readily than Type I
– Short-term contractions (force and power)
Muscle-fiber Types: Intermediate
 Type IIa-Intermediate muscle fibers
– Have a high capacity for both fast anaerobic
and slow aerobic movements
– Are more efficient at using oxygen to generate
ATP to fuel continuous muscle contractions
due to their higher concentrations of
myoglobin, larger number of capillaries, and
higher mitochondrial enzyme activity.
– Adaptable based upon the training stimulus.
A Photomicrograph Showing Type I,
Type IIa, and Type IIx Muscle Fibers
Type I (black), type IIa (white), and type IIx (gray) muscle fibers
Muscle-fiber Distribution
Muscle-fiber distribution is largely determined
by genetics.
• Most people have about equal percentages of
FT and ST fibers.
• Persons better at low-intensity endurance
activities may have a larger percentage of ST
fibers.
• Persons better at high-intensity, sudden bursts of
activity probably have a larger percentage of FT
fibers.
• Intermediate fibers can be trained to do either.
Muscle-fiber Response to Training
 All three muscle-fiber types are highly trainable.
– Adapt to the specific demand placed on them
– Muscle-fiber types are recruited sequentially in response
to force generation: ST then FT
– Increasing muscular strength assists endurance
performance.
– Increasing muscular endurance may interfere with
strength/power performance.
– Training endurance and strength separately appears to
lesson interference (e.g. work endurance for legs the
same day as upper body strength training and visa
versa)
Muscle Force
 The amount of force generated during
a muscle group’s contraction depends
on the following:
– The size of the individual muscle fiber (the
larger the fiber, the greater the force
during contraction)
– The number of muscle fibers recruited
(more fibers equal more force)
– The length of the muscle fiber prior to
contraction (a muscle generates maximum
force when it begins its contraction at 1.2
times its resting length)
– The speed of contraction (the slower the
movement, the more force that is
produced)
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Chronic Adaptations: Resistance training
 Neural adaptations
– Improved motor unit recruitment
patterns
– Improved motor learning
– Neural adaptations are predominant
for first 8-10 weeks) with little or no
change in muscle cross-sectional area
 Hypertrophy of fast-twitch fibers
predominates after 10 weeks of training
 Increased size and number of actin and
myosin filaments
 Increased lean body mass
 Increased connective tissue strength
 Decreased risk of joint injury
 Increased bone mineral density
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Factors promoting muscle hypertrophy
 Mechanical tension
– increased intensity represents overload.
 Muscle Damage
– inflammatory response stimulates satellite cell growth process.
 Metabolic stress
– Anaerobic by-products stimulate hormonal factors leading to
hypertrophy (e.g. H+, lactate, Pi).
– Could explain how body builder’s high volume workouts initiate
growth.
Source: Bubbico, A. & Kravitz, L. (2011). Muscle hypertrophy: new insights and training recommendations. IDEA
Fitness Journal. 8 (10): 23-26
Muscle hypertrophy: before & after resistance training
Other research related to muscle hypertrophy
 Upper vs. lower body growth rates
– Upper body appears to hypertrophy faster than lower body.
 Ideal intensity for hypertrophy
– 80-95% 1RM
 Difference in strength/power training vs body building
training
– Strength/Power have more hypertrophy in Type II fibers
– Body builders have hypertrophy in both Type I & II fibers
 Single or multi-joint exercises better for growth
– Multi-joint increase anabolic hormone
Source: Bubbico, A. & Kravitz, L. (2011). Muscle hypertrophy: new insights and training recommendations. IDEA
Fitness Journal. 8 (10): 23-26
Muscle Soreness
There are generally two types of muscle soreness
 Acute Muscle Soreness:
– Due to metabolite build-up in muscles.
– Causes “stiffness” soon after exercise bout but goes away quickly.
– Reduce this type of soreness with cool-down and post exercise
stretching.
 Delayed onset muscle soreness
– Peaks 24-48 hours after starting an exercise program, progressing too
quickly, or doing something new.
– Exacerbated by eccentric contractions and overstretching.
– It does go away in a few days (about a week).
– Attempt to reduce DOMS by starting at a low intensity and progressing
slowly through the first few weeks while minimizing eccentric actions.
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Summary of Muscle System




Skeletal muscles produce force for movement and stabilization.
The contractile unit of the muscle is the sarcomere.
The sliding filament model explains how muscles produce force.
The motor unit is an important concept which explains how muscle
fibers work together to produce smooth and controlled
movements.
 Changes in force production and muscular endurance can be
explained by muscle fiber types (I, IIx, IIa), motor unit recruitment
patterns (asynchronic vs synchronic) and changes to muscle
structure (hypertrophy and hyperplasia).
 A variety of factors contribute to muscle hypertrophy.
 There are two types of muscle soreness-acute and DOMS
Endocrine System
System of glands that secrete hormones that control
bodily function:
• Consists of host organs, chemical messengers,
target cells.
• Target cells bind specifically to hormones.
• Regulates body functions (growth, metabolism, and
response to stress).
Endocrine Glands
Primary glands of the endocrine system
include:
 Pituitary “master” gland
 Hypothalamus
 Thyroid gland
 Adrenal gland
Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins
Endocrine Glands
Pituitary gland: Master control gland. Secretes the
following hormones related to exercise:
– Growth Hormone (GH)- major anabolic agent
– Adrenocorticotropic hormone (ACH)-stimulates
adrenal glands
– Thyroid-stimulating hormone (TSH) -stimulates
thyroid
– Follicle-stimulating hormone (FSH) and
Luteinizing hormone (LH)-stimulates sex organs.
Endocrine Glands
 Thyroid gland: Regulates metabolism.
 Adrenal glands:
– Epinephrine (a.k.a. adrenaline) and Norepinephrine. “Fightor-Flight” hormone. Epinephrine is released during exercise,
which increases heart rate, elevates blood glucose, and opens
airways.
– Cortisol produced in adrenal is main catabolic and antiinflammatory agent.
– Testosterone is produced in adrenal glands and testes; men
produce 10 times more than women. Major anabolic agent.
– Estrogen is produced in adrenal glands and ovaries. Women
produce significantly more than men.
Blood Glucose Control
 Control of blood glucose levels regulated by the
pancreas to prevent wide swings in blood glucose
levels.
 Insulin: Brings glucose into cells from blood stream,
resulting in net drop in blood sugar levels.
 Glucagon: Signals the liver and muscles to break
down and release glycogen stores; results in net rise
of blood sugar levels.
 Exercise improves body’s utilization of glucose.
Summary of NASM Chapter 2
 The three components of the kinetic chain all work together
to produce movement.
 The nervous system and endocrine systems represent
controlling factors.
 The nervous is composed of billions of neurons that transfer
information throughout the body, through two interdependent
systems: the CNS and the PNS.
 The skeletal system is the body’s framework and is made up
of bones and joints in two divisions: axial and appendicular.
 The muscular system is made up of many individual fibers
attached to bones by way of the tendons. Muscles generate
force through neural activation, the sliding filament model,
and excitation–contraction coupling.