Bone, Muscle, and Connective Tissue Adaptations to Physical Activity

1. Bone, Muscle, and Connective Tissue Adaptations to Physical Activity

2. Functions of Bone • Support: bone provides a framework for the body by supporting soft tissues and providing points of attachment or most of the skeletal muscles. • Protection: bones protect many internal organs from injury very well, such as the brain and spinal cord. In addition, the heart, lungs, and reproductive organs are given some degree of protection. • Movement: most skeletal muscles attach to bones. When the muscles contract, they pull on bones to activate lever systems, and movement is produced.

3. Functions of Bone • Mineral Homeostasis: bone tissue stores a number of minerals, particularly calcium and phosphorus. Under control of the endocrine system, bone releases the minerals into the blood or stores the minerals in bone matrix to maintain critical mineral balances. • Blood Cell Production: in all bones of the infant and certain bones of the adult, a connective tissue known as red marrow produces blood cells by the process of hematopoiesis. • Storage of Energy: in some bones, yellow bone marrow stores lipids, creating an important energy reserve for the body.

4. Anatomy: Structure of Bone • Diaphysis: shaft or long main portion of a bone. • Epiphysis: end of a long bone. The two ends together are called the epiphyses. Each epiphysis is covered with articular cartilage. • Metaphysis: the region of mature bone where the diaphysis meets the epiphysis

5. Anatomy: Structure of Bone • Epiphyseal Plate: In a growing bone, the epiphyseal plate is formed of hyaline cartilage divided into four zones of cells. Under the influence of growth hormone, the plate continues to grow, giving length to the bone. When bone growth exceeds cartilage growth, beginning at puberty, the epiphyseal plate is slowly lost. Growth of long bones stops when the cartilage is completely gone. 

6. Anatomy: Structure of Bone • Articular Cartilage: covers the surface of bones forming a synovial joint • Medullary Cavity: The medullary (marrow) cavity is the space within the bone containing either red or yellow bone marrow. Red bone marrow consists of blood while yellow marrow consists of adipose tissue.

7. Anatomy: Structure of Bone • Two Types of Bone Tissue: • Compact or Cortical Bone: it forms the external layer of all bones, providing protection and support and helps the long bone resist the stress of weight applied to them. Contains the Haversian system which is composed of bone cells, nerves, blood, and lymph tissue. • Spongy Bone: the porous inner layer of bone; found at the ends of long bones and is less dense than compact bone. Contains red bone marrow.

8. Spongy Bone

9. Bone Marrow • Bone marrow is soft fatty tissue found inside the long bones of the body. It contains the following: • Red Marrow: red and white blood cells and platelets. • Yellow Marrow: fat and connective tissue and produces some white blood cells • People are born with only red bone marrow. As a person matures, the red marrow in many of the bones is replaced by yellow marrow. • By adulthood, only about half of the bone marrow is red. • Red bone marrow is found mostly in the ribs, breastbone, shoulder blades, collarbones, hip bones, skull, and spine

10. Location of Bone Marrow

11. Bone Growth and Remodeling • Ossification: bone growth due to an increase in bone cells • Longitudinal growth occurs at the epiphyseal plate (cartilage at the end of the long bone) • Bone is very dynamic and metabolically active • It adapts to mechanical loads placed on it through a process called bone remodeling

12. Bone Remodeling • Bone Remodeling: ongoing replacement of old bone tissue by new bone tissue. It occurs as a delicate balance between bone resorption (removal of old bone) by osteoclasts and bone formation by osteoblasts. It is responsible for bone strength throughout our life.

13. Bone Remodeling Cells • Three types of bone remodeling cells: • Osteoclasts, Osteoblasts, and Osteocytes. • Osteoclasts: • Bone destroying cells that cause resorption • Osteoblasts: • Bone forming cells that secrete collagen • Osteocytes: • Mature osteoblasts that regulate bone remodeling

14. Bone Remodeling • During childhood and the beginning of adulthood, bone becomes larger, heavier and denser, bone formation is then more important than bone resorption. • In older adults, bone resorption is greater than bone formation, resulting in a reduction in bone mineral density

15. Bone Mass • Bone Mass: amount of bone tissue in the skeleton, can keep growing until age 30. At that point, bones have reached their maximum strength and density, known as Maximal Peak Bone Density. • During childhood and adolescence, much more bone is deposited than withdrawn which makes it the best time to "invest" in one's bone health.

16. Factors Affecting Peak Bone Mass • Gender: peak bone mass tends to be higher in men than in women. Before puberty, boys and girls acquire bone mass at similar rates. After puberty, however, men tend to acquire greater bone mass than women • Hormones: estrogen has an effect on peak bone mass. • Nutrition: calcium is essential for bone health

17. Factors Affecting Peak Bone Mass • Physical Activity: girls and boys and young adults who exercise regularly generally achieve greater peak bone mass than those who do not. Women and men age 30 and older can help prevent bone loss with regular exercise. The best activity for your bones are exercises that force you to work against gravity • Weight training, walking, hiking, jogging, climbing stairs, playing tennis, dancing • Lifestyle: smoking has been linked to low bone density

18. Regulation of Bone Remodeling • The hormones parathyroid hormone (PTH) and calcitonin (CT), as well as Vitamin D, are the principal regulators of blood calcium concentrations • Parathyroid Hormone increases: • Bone resorption • Calcium reabsorption by the kidneys • Absorption of calcium by the small intestine(in conjunction with vitamin D)

19. Regulation of Bone Remodeling • Vitamin D: • Tends to increase the recruitment of osteoclasts, and also plays a part in the mineralization of bone matrix. • A lack of Vitamin D results in osteomalacia (impaired mineralization) and too much Vitamin D entails bone loss.  • Many other important factors are involved in bone remodeling such as estrogen, progesterone and androgens (anabolic hormones)

20. Bone Repair • Hematoma formation (clot formation) • Callus formation: mass of tissue that forms at a fracture site and connects the broken ends of the bone. • Blood vessels grow into clot in hematoma. • Macrophages (white blood cells) clean up debris • Osteoclasts break down dead tissue, fibroblasts produce collagen and granulation tissue. • Cartilage is produced within the collagen • Osteoblasts invade • New bone is formed. • Osteoblasts continue to work on outside of bone • Bone/cartilage collar stabilizes two pieces

22. Connective Tissue • A tissue that connects, supports, binds, or separates other tissues or organs. Mostly made up of collagen. • Examples of Connective Tissue: • Bone • Tendon • Ligament • Cartilage • Fat

23. Collagen • Most abundant protein in our body • Main protein in connective tissue • There is no organ or tissue which does not have collagen • Responsible for skin elasticity • It is also used in cosmetic surgery, for example lip enhancement

24. Tendon • Tough tissue that connects a muscle with a bone. • Tendons transfer the tension created by the muscle to the bone, causing movement. • Collagen forms most of the tendon • Tendon has a direct blood supply, but not very metabolically active because it contains very few cells. • Slow to heal

25. Ligament • Connects bone to bone providing support to the joint • Contains collagen and the protein Elastin which allow ligaments some extensibility. • Ligaments have a direct blood supply • Slow to heal

26. Cartilage • Rubbery, fibrous and dense, harder than ligaments, softer than bone • Found on the ends of bones • Shock absorber • Aids in attachment of muscles to the skeleton, • Provides a smooth articulating surface preventing two ends of bones from rubbing together and grating • Lacks a blood supply • Relies on synovial fluid for nourishment

27. Stimulating New Bone Formation • Minimal Essential Strain (MES): • Threshold stimulus that initiates new bone formation • Must be weight bearing activities • If force reaches or exceeds this threshold, osteoblasts go to that region of bone and secrete collagen. • If a large force is applied to the bone, the bone must be able to handle the force. • 1/10 of the force required to fracture a bone.

28. How to Stimulate Bone Formation • Specificity of Loading • Exercise Selection • Progressive Overload • Training Variation

29. Specificity of Loading • Selecting exercises that directly load a particular region of the skeleton • Walking and running loads the spine, pelvic girdle, femur, tibia, and fibula

30. Exercise Selection • Selecting exercises that incorporate many muscle groups, are multijoint, load the spine and hips, and allow for greater loads • Squat, DB Chest Press, Lunge, DB Shoulder Press • Single joint exercises should be limited

31. Progressive Overload and Training Variation • Progressive Overload: • Gradually overloading connective tissue as they become accustomed to the stimuli • Placing greater than normal demands on body • Training Variation • Use a variety of exercises to stimulate new bone formation • MB Lunge, BB Front Squat, DB Step-Up

32. Mechanical Loading • Mechanical loading creates deformation of specific regions of the skeleton by bending, using torque, or compressing forces created by muscular contractions on the tendinous insertion of a muscle into bone. • Components include: • Magnitude of Load: intensity (weight) • Rate of Loading: speed (tempo) • Direction of Forces: changing the joint angle • Volume of Loading: reps x sets x intensity

33. Osteoporosis • A loss of bone mineral density which results in weak bones • May lead to abnormally porous bone that is more compressible like a sponge • The most common sites for fractures are the hip, spine, and wrist • When estrogen levels drop after menopause, bone loss accelerates, which is the major cause of osteoporosis in women

34. Risk Factors For Osteoporosis • Female • Caucasian • Thin and small body frame • Family history of osteoporosis • Cigarette smoking • Lack of weight bearing exercise • Diet low in calcium • Vitamin D deficiency • Excessive alcohol consumption • Chemotherapy

35. Summary • Weight training can increase skeletal muscle mass, force, and metabolic capacity. • The extent of tissue adaptation (connective tissue) is related to the degree of deformation primarily by Intensity of training. • Stronger muscles pull harder on their bony attachments and cause an increase in bone mass and collagen