Lecture 2.8

Lecture Information

  • Lecture Title: Osteoporosis & The Effect of Exercise on Bone

  • Course: PSIO 201

  • Instructor: Tim Maley, PhD

  • Contact: maleytim@arizona.edu

  • Office: Gittings 113

Lecture Objectives

  1. Mechanisms of Exercise Effects on Bone Mass

    • Describe how exercise impacts bone mass.

  2. Mechanical Stress Impact on Bone Mass

    • Explain the relationship between mechanical stress and bone mass changes.

  3. Understanding Osteoporosis

    • Define osteoporosis and identify its risk factors.

Bone Remodeling During Different Life Stages

  • Bone Mass Changes:

    • Peak bone mass typically reached by age 30.

    • Men typically have higher total bone calcium than women.

    • Increased risk of fractures with reduced bone mass as age advances.

Factors Influencing Bone Health

  1. Dietary Factors

    • Importance of calcium and vitamin D.

  2. Hormonal Influence

    • Role of estrogen, testosterone, and other hormones on bone density.

  3. Exercise

    • Mechanical loading affects bone density.

Mechanisms of Bone Adaptation to Exercise

  • Change Response:

    • Bone adapts to stresses encountered through muscle pulling and ground impacts.

Bone Types and Fracture Risk

  • Spongy vs. Compact Bone

    • Spongy bone is more metabolically active and responds more efficiently to mechanical loading.

    • High fracture risk in areas rich in spongy bone (e.g., hip, wrist, spine).

Role of Exercise in Bone Health

  • Fracture Threshold Management:

    • Early exercise increases peak bone mass.

    • Late-life exercise helps prevent bone loss.

  • Additional Benefits of Exercise:

    • Enhances strength, balance, and coordination—reducing fall risk.

Mechanisms of Exercise-Induced Bone Changes

  1. Mechanocoupling

  2. Biochemical Coupling

  3. Signal Transmission

  4. Bone Cell Responses

    • Mechanical force triggers osteocyte response leading to osteoblast proliferation, enhancing bone formation over resorption.

Impact of Exercise in Space

  • Astronaut Training:

    • Astronauts exercise for at least 2 hours daily to mitigate bone loss.

    • Monthly BMD decrease of 1-2% experienced in space.

Key Takeaway Messages

  1. Adaptation to Stress:

    • Bone adapts to mechanical stresses from muscle pull and ground impact.

  2. Activity of Spongy Bone:

    • Metabolically active spongy bone can gain or lose density more rapidly and is more prone to fractures.

  3. Osteocyte Role:

    • Osteocytes sense applied forces, leading to increased bone formation through osteoblast activation.

Osteoporosis Overview

  • Definition and Characteristics:

    • Osteoporosis results in reduced bone mass, increased fracture risk with normal collagen and mineral proportions present.

  • Imaging Studies:

    • Presentation of normal vs. osteoporotic bone using scanning electron microscopy highlights structural changes.

Risk Factors of Osteoporosis

  • Nutritional Deficiencies:

    • Calcium and Vitamin D不足.

  • Age and Gender:

    • Increased risk in older age, particularly females.

  • Body Frame Size:

    • Smaller body frames present higher risk.

  • Lifestyle Factors:

    • Lack of exercise, smoking, high alcohol intake, and drug use (e.g., cortisone) contribute to higher risk.

  • Medical Conditions:

    • History of anorexia, hormonal changes post-menopause, and family history.

Notable Bone Diseases

  1. Osteoporosis:

    • Decreased density and increased fracture risk without pain unless fractures occur.

  2. Osteomalacia:

    • Inadequate bone mineralization due to vitamin D deficiency; seen with bone pain.

  3. Osteogenesis Imperfecta:

    • Genetic condition leading to brittle bones and high fracture risks in early life.

Suggested Learning Activities

  • Graph bone mass changes throughout the lifespan.

  • Create a flowchart of the mechanical loading response mechanism.