1	Chapter 4: Bone, Muscle, Connective Tissue Adaptations to Physical Activity
2	Three components of the musculoskeletal system Bone – structural support for the system Skeletal Muscle – contains contractile units that convert chemical energy into mechanical energy Intervening Connective Tissue – transmit forces from the muscle to the boney attachments, the levers.
3	Stressing the Musculoskeletal System Each of the three components must adapt to the stress in a coordinated way to prserve the strength and integrity of the whole force-generating system Muscles adapt rapidly, but bone, joint structures, and connective tissue lag behind in adaptation.
4	Adaptation of bone to exercise Bone is classified as a connective tissue Bone becomes mineralized and rigid for support Is an active tissue and sensitive to forces it experiences Forces can be bending forces, compressive forces, torsional forces, or the forces created by muscular contraction.
5	The Biology of bone formation Osteoblasts move to area of strain on the bone and begin the modeling process. They secrete collagen which increases strength of the bone Form a bone matrix between the bone cells The protein matrix eventually mineralizes as calcium phosphate Modeling occurs on the periosteum
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7	Adaptation of bone to mechanical loading Occurs at different rates in the axial skeleton and appendicular skeleton, owing to different amounts of trabecular (spongy) bone and cortical (compact) bone. Cortical bone is dense and forms a compact outer shell Trabecular bone forms plates that bridge the cortical bone and have spaces between the plates occupied by bone marrow. Vertebral bones are 70% trabecular And only in marrow cavities and ends of long bones.
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9	Stimulus for New Bone Formation Minimal essential strain (MES) is the threshold stimulus that initiates new bone formation An increase in the intensity of an activity over normal daily living are likely to be >MES, while young people may need higher intensities than older or sedentary people. Weight bearing exercises provide greater stress to the body.
10	Forces that reach or exceed a threshold stimulus initiate new bone formation in the area experiencing the mechanical strain. Page 60
11	Strain Is a function of the force per unit area of bone. 2. MES is thought to be about 1/10^th the force necessary to fracture the bone. 3. Laying down new bone at the periosteum makes the diameter bigger and the surface area larger to help dissipate forces.
12	Effects of Physical Activity and Immobility on Bone As the muscles get larger and thus the physiological cross-sectional area, which is directly related to the strength of the muscle, the greater the stress on the bone. The loss of bone (mineral) density following a period of reduced loading or immobility appears to occur at a more rapid rate than the formation of new bone.
13	"3." 3. Rapid removal of calcium from bone occurs after only a couple weeks of bed rest. 4. The absence of weight bearing results in a greater influence on the vertebral bone loss than the absence of muscular contractions. 5. Vertebral bone loss can be avoided by 3 hours of quiet standing per day.
14	Important Training concepts for Stimulating New Bone Formation
15	Specificity of Loading Employing exercises that directly load a particular region of the skeleton. If the forces are large enough they will stimulate bone growth in the area receiving the strain. Running stimulates bone density on the femur but not on the wrist.
16	Osteoporosis A disease in which bone mineral density and bone mass become reduced to critically low levels. Forces that would have been absorbed before can cause fractures. Individuals should maximize their peak bone mineral density early in adulthood VB, Basketball, gymnastics load the spine at clinically relevant sites such as hip and spine. Stimulus is independent of reproductive hormonal status.
17	Exercise Selection Should involve many muscle groups in one exercise (multijoint), direct force vectors through the spine and hip, and allow greater absolute loads to be used in training (structural exercises) Single joint or isolated exercises should be limited
18	Progressive Overload As used in strength development the principle applies to strengthening bones. Bones adapt to the stresses making it strong enough to handle higher intensity loads. Stress Fractures – microfractures in bone due to structural fatigue may develop when a force is routinely applied to a bone before it has had a chance to adapt Other excesses include tendinitis, and muscle injuries and take weeks or months to heal.
19	Young bone more responsive to exercise than mature sedentary bones Adolescent elite weightlifters had levels of bone mineralization greater than the untrained adults. Young bone is more responsive to osteogenic stimuli People should try to elevate their peak bone mass while young adults when mechanisms for bone growth are optimal
20	Training Variation Increases sensitivity to training and adaptation Bone compensates for new strain patterns The collagen fibers within the matrix change to conform to the new lines of stress This changes the distribution of force vectors
21	Stimulating bone formation Use exercises that directly load particular regions of the skeleton Use structural exercises, that is, exercises that involve many muscle groups at once, direct force vectors through the spine and hip, and allow greater absolute loads to be used in training. Progressively overload the musculoskeletal system, and progressively increase the load as the tissues become accustomed to the stimulus. Vary exercise selection, changing the distribution of the force vectors to continually present a unique stimulus for new bone formation.
22	Programs designed to stimulate new bone formation should incorporate the concepts of specificity of loading, proper exercise selection, progressive overload, and variation. The exercises selected should be structural and weight bearing
23	The Essential Components of Mechanical Loading Magnitude of the load (intensity) – the greater the magnitude of the load, the greater the stimulus for bone growth Rate of loading – Higher rates of contraction enhance the stimulus for bone growth Direction of the forces – Alteration of the normal pattern of bone loading with other variables held constant stimulates bone growth. Volume of loading (number of repetitions)
24	Mechanical Loading from Resistance Exercise Longitudinal studies of resistance training does not show the magnitude loading, rate of loading and type of exercises used by competitive strength athletes. Magnitude of response remains unclear
25	Mechanical loading from Aerobic Exercise Most successful programs to stimulate bone growth are involve more intense physical activities such as rowing, stair climbing, running and running with weight packs or vests. Activity must be more intense than normal daily activities Activity must systematically increase in intensity to continue to stimulate bone Interval training techniques allow for a higher intensity of activity.
26	Mechanical Loading for Athletes Incorporate into training for muscle strength and hypertrophy components of mechanical loading.
27	Table 4.1 Exercise Prescription Guidelines for Stimulating Bone Growth Variables Specific Recommendations Volume 3-6 sets of up to 10 reps Load 1-10 RM Rest 1-4 minutes Variation Typical periodization schemes, designed to increase muscle strength and size. Exercise Selection Structural exercises: squats, cleans, deadlifts, bench presses, shoulder presses
28	Mechanical Loading for Untrained or Aged People Use same precautionary guidelines that apply to prescribing resistance exercise for that population: A proper patient history Physical exam Analysis of joint stability, flexibility, and muscular strength Exercise prescription should be based on the measured physcial capabilites of the individual and his or her state of health (vision, balance, nutritional status, etc.)
29	The components of mechanical load that stimulate bone growth are the magnitude of the load (intensity), rate (speed) of loading, direction of the forces, and volume of loading (number of repetitions).
30	Adaptation of muscle to exercise Training must be specific to the desired outcome. A given activity dictates which type of muscle fibers will be recruited
31	Muscular Growth Hypertrophy is the enlargement cross-sectionally that results from resistance training An increase in the synthesis of contractile proteins, actin and myosin, within the myofibril And an increase in the number of myofibrils within a muscle fiber. The new myofilaments are added to the external layers of the myofibril, resulting in an increased diameter. Hyperplasia, an increase in the number of muscle fibers has been shown in animals, but are equivocal in humans
32	The process of hypertrophy involves both an increase in the synthesis of the contractile proteins actin and myosin within the myofibril and an increase in the number of myofibrils within a muscle fiber. The new myofilaments are added to the external layers of the myofibril, resulting in an increase in its diameter
33	Training Programs Training for strength Training for muscle size Training for muscular endurance using aerobic exercise
34	Stimulating Muscular Adaptations For Strength – High loads, few repetitions, full recovery periods For muscle size – Moderate loads, high volume (reps), short to moderate rest periods For muscular endurance – Low intensity, high volume, little recovery allowed
35	Training for strength High resistance, near-maximal contractions for a small number of repetitions with full recovery periods between each set. Elicits increases in the cross-sectional area of the exercised muscles with type II fiber areas increasing more readily and at a faster rate than type I fibers. The biochemical adaptations to strength training: significant increases in muscle glycogen, creatine phosphate, and ATP substrate stores. Also, and increase in glycolytic enzymes myokinase, and creatine kinase, which increase the speed of the reactions
36	Training for muscle size Uses moderate loads with more repetitions per set than for a strength program, but heavy enough to elicit concentric and eccentric contraction failure within 6-12 reps. The rest period is short to moderate duration, and the next set should begin before full recovery Sometimes a large number of sets of one muscle group in a single session. High overall training volume Body builders build up larger amounts of collagen and non-contractile connective tissue which increases girth, and has a lower % of Type II fibers Biochemical changes similar to strength training
37	Table 4.2 Proportion of Type II Fibers in Athletes who Perform Anaerobic Activities Type of Athlete Type II % Body builders 44% Javelin throwers 50% 800-m runners 52% Weight lifters 60% Shot-putters 62% Discus Throwers 62% Sprinters and Jumpers 63%
38	Training for muscular endurance using aerobic exercise Involves submaximal contractions extended over a large number of repetitions with little recovery allowed between each “set”. The relative intensity is very low and the overall volume is very high. Develops increases in aerobic potential in Types I and II fibers, however type I have a higher initial aerobic capacity than type II . Type II fibers increase their aerobic capacity, but type I has a greater oxidative capacity both before and after training than the type II.
39	Aerobic Endurance Training Reduced concentration of glycolytic enzymes Can reduce the hypertrophy of the hypertrophied (and nonhypertrophied) type II fibers. There is a selective hypertrophy of type I muscle fibers, but not as great as type II fiber response to resistance training. Type I fibers hypertrophy more during bodybuilding resistance programs than aerobic endurance training. There is a conversion of type IIb to IIa
40	Other adaptations to Endurance training Increase in size and number of mitochondria Higher levels of myoglobin Increased capillarization density Increased level and activity of oxidative enzymes Increase in glycogen and triglyceride stores
41	Adaptation of Connective Tissue to Exercise Connective tissues of the musculoskeletal system consists of: Tendons Ligaments Fascia Cartilage Link between the muscles and the bones Connective tissue can adapt to exercise
42	Collagen Fiber Primary structural component of all connective tissues in the musculoskeletal system is the collagen fiber. Collagen of the bone, tendon, and ligaments consists of Type I collagen, a protein. 3. Strength of tendons and ligaments comes from the internal architecture of the collagen fiber 4. Collagen fiber is a parallel arrangement of protein strands that have bunched together in the extracellular space because of mutual attraction and then chemically cross-linked to form a stable structure.
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44	Biology of Tendons, Ligaments, and Fascia Tendons and ligaments are composed of tightly packed, parallel arrangements of collagen bundles. Tendons and ligaments contain very few active cells, and require a low amount of oxygen and nutrients. They do have a blood supply. Ligaments contain elastin, an extensible protein; flexible and strong
45	"5." 5. Tendons and ligaments attach directly to cartilage or bone with a blend of collagen and other CT fibers. 6. Fascia, the fibrous CT that surround and separate the fasciculi and muscle fibers, form sheets of fibrocollagenous support tissue: endomysium, perimysium, epimysium. 7. The different fascial layers converge together near the end of the muscle to form a tendon, which attaches to the bone surface.
46	Biology of Cartilage Cartilage, a dense CT of cells embedded in a firm matrix. Functions include: Provide a smooth articulating surface at the interface of bones in a joint Act as a shock absorber for forces directed through the joint Aid in the attachment of muscle to the skeleton
47	"3." 3. Cartilage does not have its own blood supply. 4. Condrocytes depend on synovial fluid for oxygen and nutrients 5. Cartilage does not easily repair 6. Types of cartilage: Hyaline – found in the joints, articular Contains type II collagen fibers in a gel-like matrix called ground substance Contains glycoaminoglycans and proteoglycans that attract a great deal of fluid into the matrix Proteoglycans are like compressed springs in matrix 7. Type of cartilage: Fibrous Intervertebral disks, junctions of tendons and bones Consist of type I and II collagen fibers in parallel
48	Effects of Physical Activity on Tendons, Ligaments, and Fascia Primary stimulus for CT growth is the mechanical forces created during physical activity Degree of tissue adaptation proportional to intensity of exercise stimulus and the frequency of the stimulus Increased muscle forces result in adaptation of the CT: At junctions of tendon or ligament and bone Within the body of the tendon or ligament In the network of fascia within skeletal muscle.
49	"4." 4. General CT response to aerobic endurance exercise is increased collagen metabolism, however no net gain in collagen, just replacement 5. Metabolic turnover is very slow due to poor vascularity and circulation 6. Low to moderate intensity does not change collagen content of CT, but High intensity loading of the musculoskeletal system results in net growth of involved CT 7. Increased fibroblastic activity are prerequisites for muscular hypertrophy
50	A General connective tissue response to aerobic endurance is increased collagen metabolism
51	High intensity loading of the musculoskeletal system results in net growth of the involved connective tissues and reinforcement of the cartilage matrix.
52	Effects of Physical Activity on Cartilage Articular cartilage gets its nutrient supply from the synovial fluid and thus links joint mobility with joint health. Immobilization of joint prevents proper diffusion resulting in the death of chondrocytes and resorption of the cartilage matrix, which may be irreversible Mobilization of a joint prior to healing of the articular surface can be damaging to the joint.
53	Stimulating Connective Tissue Adaptations Tendons, Ligaments, Fascia Exercise of low to moderate intensity does not markedly change the collagen content of CT. High-intensity loading results in a net growth of the involved CT. Cartilage Weight-bearing forces and complete movement throught the range of motion seem to be essential for maintaining tissue viability. Moderate aerobic exercise seems adequate for increasing cartilage thickness. Strenuous exercise does not appear to cause degenerative joint disease.