Copyright 2010. PEER.tamu.edu
Exercise and Bones
Discuss these Questions:
• Are your bones all non-living
material like a rock or made of
living material like your heart?
• Once you are through growing,
do your bones stay the same
for the rest of your life?
Answers:
• Your bones are made of hard
living tissue.
• Bones are constantly being
broken down and rebuilt for
your entire life!
Basic Structure and
Function of Bones
•
Periosteum: Outer protective covering
with many blood vessels for transport of
materials.
•
Compact Bone: Made of hard mineral
material, mostly calcium. Used for support
of body, movement, and protection of
organs.
•
Spongy Layer: Mesh-like bony structure
for strength and support.
•
Bone Marrow: contains the stem cells
that gives rise to blood cells.
Bone
Periosteum
Mineral Structure of Bone
• Calcium (about 99% of all
body calcium is in bones
and teeth)
• Phosphorus
• Magnesium (about 70% of
all body magnesium is in
bone)
Note: These are all elements on the Periodic Table of the Elements
Bones are Made of Cells.
Types of Bone Cells and Their
Function:
• Osteoblasts – make the hard framework or
matrix that is made up of calcium phosphate
crystals.
• Osteocytes – “matured” osteoblasts; trapped
within bony wall that they have made around
themselves.
• Osteoclasts – break down bone; they release
acids and enzymes to dissolve crystals and a
break down hard framework or matrix.
How Does Exercise Affect the Structure of Bone?
Wolf’s Law
Bone reacts to the stresses put on it.
Athletes
• Studies have shown that weightbearing physical activity by athletes
increases bone density.
• THUS, weight-lifters have very high
bone density in their thigh bones,
while the thigh bones of swimmers
do not differ much from non-athletes.
• This is also true for animal athletes.
http://depts.washington.edu/bonebio/bo
nStrength/exercise/sports.html
Bones respond to physical stress quickly:
• Bone remodeling starts with osteoclasts breaking
down the bone to make way for new, stronger
bone.
• Then the osteoblasts follow and build the new
bone.
• Greater physical stress placed on a bone results
in more bone building by osteoblasts.
• The cycle of breaking down bones and building
bones continues as bones remodel.
This is a Cause and Effect
Relationship!
Cause or
Stimulus
Effect or
Response to
Stimulus
Greater Physical Greater Bone
Activity
Strength
Stimulus
Response
Decreases in Bone Mass
(Osteoporosis)
• Bone resorption (breakdown) can be
faster than new bone formation.
• A factor that causes this is lack of
physical stress.
• This tends to occur in:
– the elderly
– post-menopausal women
– bed-ridden people
– ASTRONAUTS!
Stop and Think:
• What do you know
about the force of
gravity?
• How do you think
gravity affects your
bones?
• Why would the
bones of astronauts
be affected by the
lack of gravity?
Space Flight Effects on Bones
• Lack of gravity decreases
mechanical stress on bone.
• Disuse of bone leads to
decreased bone density.
• Early astronauts lost up to
20% of their bone mass while
in orbit.
• Now, rigorous exercises while
in outer space can limit bone
loss.
* See slide note
*
In space, astronauts do not experience the effects
of gravity like we do here on earth. They float, so
there is no weight bearing on their bodies. While in
space an astronaut is at very high risk for losing
substantial bone mass.
Proper exercise and nutrition is what allows the astronauts to be
able to do their jobs when they are out in space for long periods.
If their muscles and bones became weak, it would be very
difficult to carry out even simple tasks. It would also increase
their risk of injury and illness.
Astronauts spend months preparing their bodies
for space exploration. They depend on specialists
like nutritionists and strength and conditioning
coaches to design menus and work outs that can
help them stay strong and healthy while in space.
NASA is currently working on an Exercise
Countermeasures Project to help promote the
health and safety of astronauts and reduce the
effects of zero gravity.
They are studying and developing exercises that
astronauts can do while in space. They are
working to come up with equipment and workouts
that are both time and space efficient. Some of
the products of this program are depicted in the
next few slides.
The astronauts do treadmill
exercises that include walking,
running, deep knee bends, and
resistive exercises. These
exercises are designed to
stimulate bone mass,
cardiovascular fitness, muscle
endurance, and the
neurophysiologic pathways and
reflexes required for walking on
Earth or other planetary surfaces.
The astronaut depicted to the right
is doing “resistive training.” He is
strapped into the device and weight
is imparted on his body to help
simulate the weight he would normally
experience while on earth. This
particular machine can impart up
to 300 lbs of pressure.
The astronaut on the left is
doing cycle ergometry. This
exercise helps to improve
endurance and strengthen her
bones when resistance is
adequately applied .
What is he doing?
Image from Nasa webpage
http://www.nasa.gov/mission_pages/station/science/eZLS_treadmill_010306.html
*
Rehabilitation using a
Water treadmill
If gravity is good for bones, why would you want to put a
treadmill in a tank of water that reduces gravity?
*
How can you
strengthen and protect
bones?
Defense
Against Osteoporosis
• Studies have shown
that even mild activity
in nursing homes not
only slows bone loss in
the elderly, but even
results in bone buildup
over 36 months!
Young People
Need Exercise Too
• Remember: your bones are being built
as you grow. Bones are especially
vulnerable to poor nutrition and lack of
exercise at your age.
• Do you get sufficient exercise?
Animals like pets also need
regular exercise to stay
strong and healthy!
• Studies have shown that
regular exercise is important to
avoid illness and encourage
normal behavior patterns in
most pet animals.
You and your pet will feel better
and stay stronger when you are
both physically fit!