Muscles
Locomotion
Locomotion

Organization of muscles into musculoskeletal
systems allows the of translation cellular
contraction into animal locomotion.

Musculoskeletal system interacts with the
nervous system to control position and
movement of appendages.
Locomotion
Invertebrates

Most worm-like inverts crawl using
overlapping layers of muscle fibers.

Hydrostatic skeleton:
◦ Simple muscles work in combination with
fluid-filled internal chamber.
Nematodes
Earthworms
Locomotor striated muscles organized
into circular longitudinal layers.
 Segmented = more control

◦ Peristaltic waves of contraction
Earthworms
Squid

One of fastest
aquatic invertebrates

Circular muscle that
surrounds the mantle
is composed of 3
layers
Squid

Jet propulsion:
◦ Water enters mantle
◦ Mantle contracts – ejected thru siphon
◦ Creates flume of water, pushing the squid forward
Vertebrates

Fish

Tetrapods:
◦
◦
◦
◦
Amphibians
Reptiles
Birds
Mammals
Fish

2 main types of muscle fibers:

White muscle:
◦ glycolytic fiber type, responsible for high
intensity, burst swimming

Red Muscle:
◦ oxidative fiber type, supports slow steady
state cruising activity.
Fish

White Muscle =
◦ 85% of muscle
◦ 60% of body mass

Red Muscle =
◦ Along Lateral Line
◦ Base of Fins
Fish

Myotome:
◦ Blocks of parallel white muscle fibers
connected by thin layers of connective tissue.
Fish

Each myotome connected to posterior
region by tendons.

Skin acts as sheath that connects different
myotomes:
◦ Integrates force of many contractile units

Contraction of a myotome generates a force
that is transmitted to the next myotome.
Muscle Contraction

Oxidative (red) & glycolytic (white)
muscles differ in contractile properties
and produce different types of movement.
Muscle Contraction

Fish:
◦ Red muscle = slow swimming
◦ White muscle = higher velocities

Pattern of sequential activation of muscle
contraction = recruitment

Determined by motor neurons, under
control of the CNS
Fish
Tetrapods

Build individual muscles using
combinations of fiber types.

Muscle fiber types are used in different
combinations to perform many distinct
styles of movement.
Tetrapods
Limb Movements

Flexion: when a limb bends at a joint

Extension: limb straightens

Induced in response to the contraction of
antagonistic muscles.
Limb Movement

Antagonistic muscles:
◦ muscles which work in opposition

Locomotor Module:
◦ all of the muscles responsible for a type of
movement.
Fiber Types

3 Main Types:
◦ Different species have different types with
different mechanical properties matched to
their biochemistry and morphology.
1.
2.
3.
Slow Oxidative (SO)
Fast Oxidative Glycolytic (FOG)
Fast Glycolytic (FG)
Fiber Types
Muscle
Description
Metabolic
Features
Slow Oxidative
(SO)
Red Muscles
Endurance Muscles
Slow Twitch
Marathoners
Fast Oxidative
Glycolytic
(FOG)
White – Pink
Oxidative based
metab.
metabolism
Fast Glycolytic
(FG)
White
Fatigue Sensitive
Fast Twitch
Quick Response
Mixed
Fatigue Resistant
Fiber Types

Fiber composition varies with:
1.
Training
2.
Muscle Type
3.
Animal species / athlete
Fiber Types
Animal
Sea Otter
Dolphin
Sea Lion
Narwhal
%SO
56
43
44
87
%FOG
2
10
18
?
%FG
42
47
39
13
Energy Metabolism & Muscle Types

Muscle activity demands a great deal of
energy, mainly in the form of ATP.

Locomotor activity is supported by some
combination of anaerobic glycolysis and
mitochondrial aerobic metabolism.
Energy Metabolism & Muscle Types

These two pathways differ in 5 main
respects that determine how they
support muscle activity:
1.
2.
3.
4.
5.
Metabolic Efficiency
Rate of ATP Production
Dependence on Oxygen
Fuel Diversity
Range of Mobilization
Metabolic Efficiency
Anaerobic
Aerobic

2 ATP / Glucose

36 ATP / Glucose

Used during fast /
explosive movements

Used during
endurance events

Used during rest and
recovery periods
Rate of ATP Production
Anaerobic
Aerobic

Less Efficient

Efficient

Much Faster

Slower

Runs out of fuel fast

Sustainable

Fatigues
Dependence on Oxygen
Anaerobic

Only option when no
oxygen is present
Aerobic

Needs oxygen
During high intensity activity, oxygen cannot be
delivered to muscles fast enough to meet ATP
demands by oxidative phosphorylation and tissues
become functionally hypoxic.
Fuel Diversity

Anaerobic

Aerobic

Glycolysis relies
exclusively on
carbohydrates

Able to utilize:
◦ carbohydrates
◦ lipids (fatty acids)
◦ proteins (amino acids)
Rate of Mobilization

Muscles possess low levels of fuels that
can be oxidized immediately (glucose,
fatty acids, glycerol, free amino acids).

These fuels are consumed rapidly, so
animals must be able to mobilize stored
fuels to sustain muscle activity.

Glycogen stores mobilized much faster
than lipid stores
Mitochondrial Content

Mitochondria are the site of oxidative
phosphorylation.

Mitochondrial content is an important
determinant of aerobic capacity.
Mitochondrial Content

Mitochondrial content varies widely
among muscle types and species.
◦ High [Mitochondria] = slow twitch oxidative
◦ Lower [Mitochondria] = fast twitch glycolytic
Fiber Types

Slow Oxidative (SO):
◦ Dense with capillaries
◦ Rich in mitochondria and myoglobin

Fast Oxidative Glycolytic (FOG):
◦ Less dense in mitrochondria and myoglobin

Fast Glycolytic (FG):
◦ Least dense in mitochondria and myoglobin
Muscle Recovery

High intensity activity is fueled by
intramuscular stores of glycogen.

As fast twitch muscles undergo glycolysis,
lactate is produced.

Muscles become exhausted from a
combination of energetic shortfalls, ion
disturbances, and PH imbalance.
Muscle Recovery

Muscles must:
◦ Replenish energy stores
(glycogen, ATP, PCR)
◦ Reestablish ion gradients
(Ca2+ stores and pH)
◦ Remove lactate.
Lactate Removal
1.
Used in muscle to rebuild glycogen stores.
1.
Blood-born lactate can be oxidized by
other aerobic tissues (eg. Heart)
2.
Export lactate to be processed elsewhere.
Cori Cycle
Lactate Removal
Muscle Recovery

Oxygen consumption increase with
increasing activity.

Oxygen stores must be replenished.

Muscles must:
◦ Resynthesize ATP, PCR, and glycogen
◦ Reestablish ion gradients
◦ Repair damaged muscles
Restoring Oxygen Levels

Energy for these processes is provided by
mitochondrial oxidative phosphorylation.

Recovering animals often show elevated
rates of oxygen consumption long after
exercise has ceased = oxygen debt.
Muscle Recovery
Recovery requires both energy & oxygen.
Muscles & Locomotion
Metabolic processes must be precisely
coordinated to ensure that ATP
synthesis matches ATP demand.
Hummingbirds
Hummingbirds

Morning/ first flight - oxidizes fatty acids.
◦ After first nectar it switches to carbohydrate
utilization and lipid storage.

Actively feeding - dietary carbohydrates
◦ Stores extra surcose as glycogen and lipid.

Rest - relies on stores.
◦ Also becomes hypometabolic – lowers
body temp to reduce MR.
Hummingbirds
Salmon
Salmon

Early Stage of Migration:
◦ large fat stores

Mid Migration:
◦ begin breaking down proteins:
 muscles and intestinal tract

Late in migration:
◦ glycogen and glucose support
Salmon