Exercise and Bones

Copyright 2010. PEER.tamu.edu

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.

Wolf’s Law Bone reacts to the stresses put on it.

How Does Exercise Affect the Structure of Bone?

Athletes

• Studies have shown that weight-bearing 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/bonStrength/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 Activity

Greater Bone Strength

StimulusStimulus ResponseResponse

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 normallyexperience 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 .

Image from Nasa webpage

http://www.nasa.gov/mission_pages/station/science/eZLS_treadmill_010306.html

*What is he doing?

Rehabilitation using aWater 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!