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Introduction to Exercise Science for Fitness Professionals: Supporting the Body

Introduction to Exercise Science for Fitness Professionals
Supporting the Body
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table of contents
  1. Cover
  2. Title Page
  3. Copyright
  4. Table Of Contents
  5. Attribution and OER Revision Statement
  6. Chapter 1: Body Systems Review
    1. The Cardiovascular System
    2. The Nervous System
    3. Reflexes
    4. The Skeletal System
    5. Divisions of the Skeletal System
    6. Skeletal Muscle
    7. Divisions of the Skeletal Muscles
    8. Describing Motion and Movements
    9. Identify Anatomical Locations
  7. Chapter 2: Biomechanics and Human Movement
    1. The Basics of Biomechanics
    2. Inertia and Momentum
    3. Force
    4. Doing Work
    5. Body Levers
    6. Nervous System Control of Muscle Tension
    7. Muscle Tissue and Motion
  8. Chapter 3: Exercise Metabolism
    1. Introduction to Bioenergetics and Metabolism
    2. Overview of Metabolic Reactions
    3. Metabolic States of the Body
    4. The Cardiorespiratory System and Energy Production
    5. ATP in Living Systems
    6. Types of Muscle Fibers
    7. Exercise and Muscle Performance
    8. Nutrition, Performance, and Recovery
    9. Carbohydrate Metabolism
    10. Protein Metabolism
    11. Lipid Metabolism
  9. Chapter 4: Fitness Principles
    1. What are Physical Activity and Exercise?
    2. The Physical Activity Guidelines for Americans
    3. Components of Health-Related Fitness
    4. Principles of Adaptation and Stress
    5. FITT Principle
    6. Rest, Recovery, and Periodization
    7. Reversibility
    8. Training Volume
    9. Individual Differences
    10. Creating a Successful Fitness Plan
    11. Additional Safety Concerns
    12. Test Your Knowledge
  10. Chapter 5: Flexibility Training Principles
    1. What is Flexibility?
    2. Benefits of Flexibility and Stretching
    3. Improving Range of Motion
    4. Improving Flexibility
    5. Creating an Effective Stretching Program
    6. Assessing Your Flexibility
    7. Test Your Knowledge
  11. Chapter 6: Cardiorespiratory Training Principles
    1. What are the Cardiovascular and Respiratory Systems?
    2. Introduction: The Cardiovascular System
    3. Introduction: The Respiratory System
    4. The Process of Breathing and Respiratory Function
    5. Modifications to Breathing
    6. Changes in the CR System
    7. Measuring Heart Rate
    8. Measuring Intensity
    9. Cardiorespiratory Fitness Assessment
    10. Test Your Knowledge
  12. Chapter 7: Core and Balance Training Principles
    1. Lumbar Spine
    2. Abdomen
    3. The Pelvic Girdle
    4. Creating Movement at the Hip
    5. Balance
    6. Center of Gravity
    7. Supporting the Body
    8. Friction in Joints
    9. Human Stability
    10. Guidelines for Core and Balance Training
  13. Chapter 8: Plyometrics, Speed, Agility, and Quickness Training Principles
    1. Plyometric Exercises
    2. Variables of Plyometric Training
    3. Progressing a Plyometric Program
    4. Speed, Agility, and Quickness
    5. Speed
    6. Agility
    7. Quickness
  14. Chapter 9: Resistance Training Principles
    1. Resistance Exercise Programming
    2. Exercise Order
    3. Types of Resistance Training
    4. Basics of Form during Resistance Training
    5. Resistance Training Systems
    6. Resistance Training Conclusion
    7. Test Your Knowledge
  15. References
  16. Glossary
  17. MARC Record

63

Supporting the Body

Lawrence Davis

Support Force (Normal Force)

When standing on the ground gravity is pulling you down, but you aren’t falling. In fact you are in static equilibrium so the ground must be providing a supporting force that balances your weight. The ground provides that force in response to compression caused by your weight. When solid objects push back against forces that are deforming them we call that responsive push-back the Normal Force.

Reinforcement Activity

Push your finger down into your palm and feel the resistance from your palm.

That resistance is the normal force.

When you pull your finger away from your palm, the normal force from your palm goes away.

Everyday Example[1]

In the diagram below, we see a person placing a bag of dog food on a table. When the bag of dog food is placed on the table, and the person lets go, how does the table exert the force necessary to balance the weight of the bag? While you wouldn’t see it with your naked eye, the table sags slightly under the load (weight of the bag). This would be noticeable if the load were placed on a thin plywood table, but even a sturdy oak table deforms when a force is applied to it.  That resistance to deformation causes a restoring force much like a deformed spring (or a trampoline or diving board). When the load is placed on the table, the table sags until the restoring force becomes as large as the weight of the load, putting the load in equilibrium. The table sags quickly and the sag is slight, so we do not notice it, but it is similar to the sagging of a trampoline or a hammock when you climb on.

Figure a shows a person holding a bag of dog food just above a table. Force F subscript hand points up and force F subscript g points down. Figure b shows the bag placed on the table, which sags with the weight. Force N points up and force F subscript g points down.
The person holding the bag of dog food must supply an upward force equal in size and opposite in direction to the force of gravity on the food. The card table sags when the dog food is placed on it, much like a stiff trampoline. Elastic restoring forces in the table grow as it sags until they supply a normal force equal in size to the to the weight of the load. Image credit: University Physics

Normal Force and Weight

If you place an object on a table the normal force from the table supports the weight of the object. For this reason normal force is sometimes called support force. However, normal is another word for perpendicular,  so we will stick with normal force because it reminds us of the important fact that the normal force always acts at an angle of 90° to the surface. That does not mean the normal force always point vertically, nor is it always equal to an object’s weight. If you push horizontally on the wall, the wall pushes back (keeping your hand from moving through the wall). The force from the wall is a normal force, but it acts horizontally and is not equal to your weight.

Left: A person leans against a wall. An arrow labeled normal force points horizontally outward from the wall at the point of contact between the person and wall. Center: A person climbs up a steep snow slope in the mountains. An arrow labeled normal force points from their feet up and out, perpendicular to the slope. Right: A soldier drills a hole in a runway. Arrows point upward from each of the points of contact, her two feet and the drill bit.
Situations where normal force is not equal to the weight of the object. Adapted from Garscon Plancher” by Obiwancho, and “Trek on the Viedma Glacier” by Liam Quinn  “U.S. Air Force Chief Master Sgt. Suzan Sangster”released  by the United States Armed Forces with the ID 090815-F-3140L-048

[2][3][4]

In each situation pictured above the normal force is not equal to body weight. In the left image the normal force is less than body weight, and acting horizontally. In the middle image the normal force is less than body weight and acting at an angle. In the right image the normal force on the drill is more than it’s own weight because Master Sgt. Sangster is also pushing down on the drill. The normal force on Master Sgt. Sangster’s feet is less than her weight because she is also receiving an upward normal force from the drill handle.

Often (N) is used as a symbol for normal force, but we are using N to abbreviate for the SI force unit Newtons, so instead we will use $F_N$. The normal force comes up so often students often accidentally begin to refer to normal force as “natural force” instead, so watch out for that possible source of confusion.

Reinforcement Exercises: Normal Force

An interactive H5P element has been excluded from this version of the text. You can view it online here:
https://mhcc.pressbooks.pub/hpe172/?p=600#h5p-8


Davis, Lawrence. Body Physics: Motion to Metabolism. Open Oregon Educational Resources. https://openoregon.pressbooks.pub/bodyphysics


  1. OpenStax University Physics, University Physics Volume 1. OpenStax CNX. Jul 11, 2018 http://cnx.org/contents/d50f6e32-0fda-46ef-a362-9bd36ca7c97d@10.18 ↵
  2. "Garscon Plancher" by Obiwancho , Wikimedia Commons is licensed under CC BY-SA 3.0 ↵
  3. "U.S. Air Force Chief Master Sgt. Suzan Sangster", Wikimedia Commons is in the Public Domain,  ↵
  4. "Trek on the Viedma Glacier" by Liam Quinn , Wikimedia Commons is licensed under CC BY-SA 2.0 ↵

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Copyright © 2021

                                by Amanda Shelton

            Introduction to Exercise Science for Fitness Professionals by Amanda Shelton is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.
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