11 - Types Of
Skeletal Muscle
Contractions
Taft College
Human Physiology
Types Of Skeletal Muscle
Contractions
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Isotonic Contractions: Tension produced and overall shortening of the
muscle as a load is moved through the range of motion of the joint .
– Isotonic contractions serve to bring about movement or change in body
position. Example = flexion, extension, adduction, abduction, etc.
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Isometric Contractions: Tension but no shortening of the muscle
occurs. Energy is still used!
– Example:contractions that serve to keep the body fixed in position as in 1.
maintaining posture, 2. maintaining balance, 3. fixing a proximal joint so a
distal joint may move, 4. maintaining muscle tone.
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Most body activities involve both isotonic and isometric contractions.
Twitch: A single isotonic response as a result of a single threshold (liminal)
stimulus. (This is not the type of twitch you feel in your body due to being
tired or a chemical imbalance).
The muscle contracts quickly and then relaxes.
A twitch can be demonstrated with an instrument that produces a
myogram= a tracing of a muscle contraction or activity.
Types Of Skeletal Muscle Contractions
Isotonic Contraction =
Isometric Contraction =
Tension + Shortening of muscle
Tension, no Shortening of muscle
A Myogram of 3 Phases (Periods) of a Muscle Twitch
1.
2.
3.
Latent Period – the time from stimulation of the muscle until shortening of the muscle
begins.
The latent period is a “lag time”.
Duration = about 2 ms.
During this period of time the following events of muscle contraction are occurring:
a. Depolarization
b. Diffusion of Ca+2
c. Establishment of actin/myosin bonding
Contraction Period – Tension and shortening of the muscle occurs.
The upward tracing represents this phase.
Duration = 10-100 ms.
Relaxation Period – Muscle goes back to it resting state.
The Ca++ is actively transported back into the SR which results in relaxation.
The downward tracing represents this phase.
Duration = 10-100 ms.
•Muscles differ in the
amount of time it takes to
through 3 phases.
Ex.
eye muscles 12 millisec
= Fast Twitch Muscle
gastrocnemius 36 millisec,
soleus 100 millisec
= Slow Twitch Muscle
3 Types of Skeletal Muscle Fibers
• In humans we see 3 types of skeletal muscle fibers
classified based on :
• 1. How fast a muscle will twitch (due to how fast it splits
ATP) and,
• 2. Metabolic pathway used to generate ATP (glycolytic
(anaerobic) or oxidative).
• We will concentrate on only 2 fiber types a. slow twitch =
slow oxidative fiber and b. fast twitch = fast glycolytic fiber.
Fast & Slow Twitch Muscle Fibers
Fast Glycolytic
Fast Twitch
Slow Oxidative
Slow Twitch
Color
White = Light
Red = Dark
Size
Large fibers
few mitochondria
Small fibers
more mitochondria
Reaction
Fast (anaerobic)
Slow (aerobic)
Function
Speed
Endurance
Location
Eye muscles &
upper appendages
Postural muscles &
lower appendages
Rate of fatigue
Fast
Slow
eye muscles 12 millisec
gastrocnemius 36 millisec
soleus 100 millisec
Examples:
Table of Characteristics of Skeletal Muscle Types
Structural Features
Diameter or Fiber
Color/Myoglobin
Mitochondria
Functional Features
ATP Production
ATP use/Velocity
of Contraction
Resists Fatigue
Glycogen Stores
Order of recruitment
Slow Twitch
Slow Oxidative
Smallest
Red/large
Many
Slow Oxidative
Aerobic (O2) process
Slow
High
Low
1st
Fast Twitch
Fast Oxidative
Intermediate
Red-pink/large
Many
Fast Oxidative
Aerobic (O2) process
Fast
Intermediate
Intermediate
3rd
Fast Twitch
Fast Glycolytic
Largest
White/small
Few
Fast Glycolytic
Glycolysis (anaerobic)
Fast
Low
High
2nd
Skeletal Muscle Types
• Slow Oxidative: Maintain posture (anti-gravity
muscles), endurance running.
Back and neck muscles.
• Fast Oxidative: Walking, sprinting.
Leg muscles.
• Fast Glycolytic: Rapid, intense movements of
short duration. Ball throwing, weight lifting.
Arm muscles.
Implications for Sports
• Number of red (slow twitch) vs. white (fast twitch)
muscle fibers is hereditary
– Conditioning and training can do nothing to change the
ratio (New research may show otherwise)
– E.g. Alberto Salizaar – New York marathon winner had
92% red vs. 8% white. Other runners tend to have fewer
red and more white in comparison.
• Sprinters contain about 60% fast oxidative.
• Weight lifters have about equal amounts fast glycolytic and slow
oxidative
• Determination of muscle fiber ratios can be done by muscle
biopsy.
Other animals use of muscle cell types
• Concentrations of fast and slow twitch muscles
can be observed in other animals as well as
humans.
• The light and dark meat of a chicken has to do
with concentrations of different types of muscle
fibers.
– A chicken uses it’s breast muscle (white meat) for
short flight if at all = fast twitch. The legs (dark meat)
of a chicken serve for endurance = slow twitch.
– What type of meat would you expect to find in the
breast of a migratory duck? Dark meat = slow twitch
for endurance.
Physiology Assignment #4
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Name__________________________
Due Date ___________
Internet assignment (Attach article)
What are the implications of fast/slow
twitch muscle in sports (any sport you
wish).
• Is it possible to change the percentage of
fast twitch to slow twitch muscles you have
or is it genetically determined?
Anabolic Steroid Abuse
• Testosterone (found in men) and human
growth hormone influence muscle growth.
• Anabolic steroid drugs are testosterone-like
and are abused by athletes to increase
muscle size & strength and endurance.
– Moderate doses – no better than optimal training.
– Large doses…..damage to body.
Anabolic Steroid Abuse
• Problems:
– liver cancer, kidney cancer, heart disease,
aggressive behavior, mood swings.
– Females: sterility, facial hair, deep voice,
atrophy of breasts and uterus, menstrual
irregularities.
– Males: testes atrophy, less sperm production,
baldness.
Types of Skeletal Muscle (cont.)
•
Tetanus – sustained contraction of a muscle due to increased frequency of stimulation.
Result of a summation of twitches (a normal muscle contraction)
– When the frequency of the stimulation is such that there is no hint of reduced tension or
force between stimuli, it is called complete tetany or fused tetany. 80-100 stim/sec
– When the frequency of stimulation is reduced slightly, you can see partial muscle
relaxation occurring between contractions, this is called incomplete tetany or unfused
tetany. 20-30 stim/sec
• Incomplete tetany can result in trembling (shaky) movements of the limbs observed in some
individuals.
– Normal muscle contractions with smooth movement are a result of complete tetanic
contractions.
Twitches
Types of Skeletal Muscle (cont.)
Tension Increasing
Tr
e
pp
e
• Treppe – increased strength of contraction as muscle
“warms up” due to identical stimuli too far apart for wave
summation to occur.
• It is also known as the ‘staircase effect’, as the muscle steps
up its strength with each contraction.
How does this
myogram differ from
incomplete tetanus?
How do we know this
is not wave
summation?
Hint
Stimulus constant
Types of Skeletal Muscle (cont.)
• Treppe can be explained as follows:
• A progressive buildup of Ca++ in the sarcoplasm probably
accumulates because the stimuli release Ca++ faster than the
Ca++ pump can move them back in to the SR.
– The troponin becomes saturated for maximum binding to myosin
heads.
– Eventually the inflow and outflow of calcium ions equalize and the
strength of contraction level off
• In your warming muscles, the sarcoplasm becomes less
viscous. With more heat and the internal resistance of the
muscle lessened it allows more energy to be directed to
muscle shortening and less to overcome resistance.
– With heat from ATP splitting and other chemical reactions, the enzyme
systems become more efficient.
– This is the basis for the warm-up period for athletes.
Muscle Tone
• Tone is a sustained partial state of contraction in
the muscle.
• Tone is maintained in the body without fatigue
by the alternation of different motor units. It
serves to keep the body in a state of readiness
for activity at all times.
• It is believed that the contractions are some type
of involuntary spinal reflexes responding to
activation of stretch receptors in muscles and
tendons.
Muscle Tone
• Hypotonia – Refers to decreased or lost muscle tone,
resulting in flaccid (flattened) shape instead of round.
• Atrophy – Wasting of muscle tissue where muscle fibers
decrease in size as myofibrils are lost.
• Hypertrophy – Opposite of atrophy. Refers to an
increase in diameter of muscle fibers where myofibrils,
mitochondria, and SR are increased. No increase in # of
cells. Capillaries servicing muscle fibers are increased
too.
– Due to forceful, repetitive strength training, which results in
increased capacity for forceful contractions.
Muscle Tone
Muscle tone can be lost quickly:
• If muscle usage is prevented by a cast (disuse atrophy), or
by a severing of the nerves (denervation atrophy), the
muscle fibers begin to atrophy in just a few days.
• Prolonged inactivity can lead to degeneration of the muscle
fibers and potential replacement by scar tissue (C.T.,
including fat), which cannot be reversed when complete.
• Direct stimulation of the inactive muscle using a muscle
stimulator may prevent atrophy until the muscle is removed
from the cast or the severed nerve fibers can remake
connections.
• The important thing to realize is that muscle health is
maintained in part by utilization - “use it, or lose it!”
Smooth Muscle
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Smooth muscle is also called involuntary muscle (under ANS control)
and nonstriated muscle (lacks organized sarcomeres).
– Actin and myosin myofilaments are present but are not regularly
arranged leading to the absence of light and dark bands that cause
the striations in skeletal muscle tissue.
Characteristics of smooth muscle in comparison to skeletal muscle
Smooth muscle has:
1. 7 times less actin & myosin in smooth muscle than skeletal muscle.
2. Lower levels of ATP & creatinine phosphate
3. Fewer number of mitochondria with slow contractions.
4. Smooth muscle cells lack T-tubules. Slower onset of contraction.
5. Have poorly developed sarcoplasmic reticulum. Takes Ca++ longer to
diffuse. Also delays in transport of Ca ++ for longer contraction.
6. Contraction stimulated by a. neurotransmitters (ACh, NE by ANS),
b. hormones
c. local chemical changes (pH, O2, CO2),
d. stretching.
So smooth muscle is designed for slow reacting, but prolonged contractions.
Abnormal Contractions Of Muscle Tissue
• Spasm – A sudden involuntary muscle twitch
(contraction of short duration), usually due to a
chemical imbalance.
• Cramp – A sustained, painful, spasmodic (tetanic)
contraction of a muscle.
– Can last minutes to hours.
– Severe cramps usually occur when the muscle is
shortened (when there is little pull on the tendons).
– Usually occurs at night or after exercise.
– It is not known what actually happens at the level of a
sarcomere during a cramp. However, the pull on the
tendons of muscles are constantly monitored by sense
organs called golgi tendon organs
Abnormal Contractions Of Muscle Tissue
• Golgi tendon organs act to inhibit or “apply the brakes” to
muscular contraction to prevent the development of too great
of tensile force that could result in injury to the muscle or
tendon.
– Learning how to disinhibit (keep the golgi tendon organs
from working) may be an important part of strength
training.
– Maximal vigorous contractions in a shortened position
seems to increase the probability of cramping as you
have maximal innervation with minimal inhibition.
• How can you relieve cramps in light of this information?
– Simply forcing the muscle into its longest position
(stretching) will create tension on the golgi tendon organ.
• The inhibition caused by the golgi tendon organ will then stop the
cramp.
Abnormal Contractions Of Muscle Tissue
• Convulsions – Violent, involuntary
contractions of whole groups of muscles.
– Convulsions occur when motor neurons are
stimulated by factors such as fever, poisons,
hysteria, and changes in body chemistry due to
drug withdrawals.
– The stimulated neurons send seemingly
senseless impulses to the muscle fibers.
– This is a nervous disorder not a muscular
disorder.
Abnormal Contractions Of Muscle Tissue
• Fibrillation – Uncoordinated contraction of
individual muscle fibers so that the muscle
fails to contract smoothly.
– Cardiac muscle is most prone to this type of
activity and is recorded by electromyography.