44C H A P T E R

Bone, Muscle, and Connective Tissue Adaptation to Physical Activity

Bone, Muscle, and Connective Tissue Adaptation to Physical Activity

Chapter Outline

Adaptation of bone to exercise

Adaptation of muscle to exercise

Adaptation of connective tissue to exercise

Types of bone cells Osteoblasts - mononuclear cells found

along bone surfaces; promote bone formation, synthesis of bone matrix

Osteocytes - osteoblasts that have been incorporated into previously synthesized bone matrix

Osteoclasts - multinucleated cells derived from hemopoietic stem cells; promote bone resorption

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Bone PropertiesBone Properties

Bone size & shape are influenced by the Bone size & shape are influenced by the direction & magnitude of forces that are direction & magnitude of forces that are habitually applied to themhabitually applied to them

Bones reshape themselves based upon the Bones reshape themselves based upon the stresses placed upon themstresses placed upon them

Bone mass increases over time with Bone mass increases over time with increased stressincreased stress

Bone Architecture: Cortical and Trabecular Bone

Bone Architecture: Cortical and Trabecular Bone

Trabecular (Cancellous) bone is able to respond to mechanical stimuli more rapidly than cortical bone.

Minimal Essential Strain (MES) refers to the threshold stimulus that initiates new bone formation.

Bone Modeling in Response to Mechanical LoadingBone Modeling in Response to Mechanical Loading

Bone Remodeling Coupling, or the linked activation of

osteoblasts and osteoclasts, is the basis of bone turnover or remodeling; the continuous skeletal activity related to mineral homeostasis and bone repair

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Bone PropertiesBone Properties

Composed of calcium carbonate, calcium Composed of calcium carbonate, calcium phosphate, collagen, & waterphosphate, collagen, & water 60-70% of bone weight - calcium carbonate & calcium 60-70% of bone weight - calcium carbonate & calcium

phosphatephosphate 25-30% of bone weight - water25-30% of bone weight - water

Collagen provides some flexibility & strength in Collagen provides some flexibility & strength in resisting tensionresisting tension

Aging causes progressive loss of collagen & Aging causes progressive loss of collagen & increases brittlenessincreases brittleness

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Bone PropertiesBone Properties

Most outer bone is cortical with cancellous Most outer bone is cortical with cancellous underneathunderneath

Cortical bone – low porosity, 5 to 30% Cortical bone – low porosity, 5 to 30% nonmineralized tissuenonmineralized tissue

Cancellous – spongy, high porosity, 30 to 90%Cancellous – spongy, high porosity, 30 to 90% Cortical is stiffer & can withstand greater stress, Cortical is stiffer & can withstand greater stress,

but less strain than cancellousbut less strain than cancellous Cancellous is spongier & can undergo greater Cancellous is spongier & can undergo greater

strain before fracturingstrain before fracturing

Effects of Immobilization on Load to Failure of Bone

Due to the lack of strains, immobilization results in weakened, less mineralized bone tissue.

High load and low repetitions (i.e., resistance training)

or Low load and high repetitions

(i.e., walking, running)?

Specificity of Loading Running is a good stimulus for the femur, but not for the

wrist. Osteoporosis: disease in which bone mineral density and

mass are critically low. High impact loading during early adulthood may maximize

both bone mineral density and mass to protect individuals later in life.

Osteogenic stimuli: factors that stimulate new bone. Use exercises that direct forces thru the spine and hip,

avoid machines that isolate body parts. For ex – standing arm curls is better than a curl bench in loading spine & hip.

Follow Progressive Overloading Don’t over-train, as it may lead to stress fractures. Training variation is very good for bone.

Table 4.1 Exercise Prescription Guidelines for Stimulating Bone Growth

Variables Specific recommendations

Volume 3-6 sets of up to 10 repetitions

Load 1-10RM

Rest 1-4 min

Variation Typical periodization schemes designed to increase muscle strength and size

Exercise selection Structural exercises: squats, cleans, deadlifts, bench presses, shoulder presses

The components of mechanical load that

stimulate bone growth are

1. the magnitude of the load (intensity)

2. rate (speed) of loading

3. direction of the forces

4. volume of loading (number of repetitions).

Stimulating Muscular Adaptations

For strength: high loads, few repetitions, full recovery periods

For muscle size: moderate loads, high volume, short to moderate rest periods

For muscular endurance: low intensity, high volume, little recovery allowed

A general connective tissue

response to aerobic endurance

exercise is increased collagen

metabolism.

Specific changes within a tendon that

contribute to the increase in its cross-sectional

area and strength in response to a functional

overload include

an increase in collagen fibril diameter,

a greater number of covalent cross-links

within a fiber of increased diameter,

an increase in the number of collagen fibrils,

and

an increase in the packing density of

collagen fibrils.

Stimulating Connective Tissue Adaptations: Tendons, Ligaments, Fascia

Exercise of low to moderate intensity does not markedly change collagen content of connective tissue.

High-intensity loading results in a net growth of the involved connective tissues.

Stimulating Connective Tissue Adaptations: Cartilage

Weight-bearing forces and complete movement throughout ROM seem essential to maintain tissue viability.

Moderate aerobic exercise seems adequate for increasing cartilage thickness. Strenuous exercise does not appear to cause degenerative joint disease.

Review Increases in bone density are greatest during weight bearing

activity at a high intensities (overload). Muscular adaptations – periodization Tendon – increased collagen fibril diameter

What decreases collagen formation? Cartilage – moderate aerobic = increased thickness. Which activity will result in the greatest BMD: Rowing,

Volleyball, Basketball, Swimming, Running, Weights, Gymnastics. Greatest Cartilage thickness? Tendon Elasticity?

Lumbar BMD of Different Athletic Groups

90

95

100

105

110

115

120

Row Volleyball Basketball Swim Run Weights Gymnasics

% S

eden

tary

Con

trol

s

Sports Drinkwater, B.L. (1994)

Response and Adaptations to

Training

Adaptations to Training Chronic exercise provides a stimulus for the

systems of the body to change to better meet the demands placed upon them (BODY ADAPTS TO THE DEMANDS PLACED UPON IT)

These systems will adapt according to the level, volume and intensity of exercise training (ADAPTATION IS SPECIFIC TO THE TRAINING)

Specificity of Training

Type of Training Prescription (Aerobic vs Anaerobic

Differences within activity (Sport Specific)

Factors that AffectAdaptations to Training

Environmental factors Climate Altitude

Genetic endowment Fiber type patterns Somatotype

Adaptations FollowingExercise Training: Neuromuscular

Neuromuscular adaptations “Disinhibition” of the proprioceptors

Autogenic inhibition of the Golgi tendon organ (GTO) Training may reduce the sensitivity of these receptors to allow

for greater force production

Increase in the number of vesicles that store acetylcholine More neurotransmitter secretion Greater force production Improvement of recruitment patterns

Adaptations FollowingExercise Training: Muscular

Muscle fiber type adaptations Normal recruitment pattern: Type I IIa IIb More precise and efficient mode of recruitment

Less neural activity is required to produce any level of submaximal force measured by electromyography

Increased synchronization increases the amount of time that maximal force output can be sustained

Fiber “transformation” (IIb IIa) may also result in increased or altered recruitment patterns

Table 4.2 Proportion of Type II Fibers in Athletes Who Perform Anaerobic Activities

Type of athlete Type II fibers

Bodybuilders 44%

Javelin throwers 50%

800-m runners 52%

Weightlifters 60%

Shot-putters 62%

Discus throwers 63%

Sprinters and 63% jumpers

Specific Adaptations from Resistance Training Changes in fiber area Hypertrophy of the muscle fibers Muscle fiber “transformation”

Type IIb Type IIa fibers

Increased high energy phosphate pool Improved motor unit firing synchronization Improved neural function

Neuroendrocrine Adaptations Increased synthesis of hormones Improved transport of hormones Reduced time needed for clearance of tissues Reduced amount of hormonal degradation Increased number of hormones receptors in the

tissues Increased magnitude of signal sent to the cell

nucleus Improved interaction with cell nucleus

Specific Adaptations fromAerobic Training Increased myoglobin content Increased oxidation of glycogen Increased VO2 and a-vO2 difference Biochemical changes in Type I and II

muscle fibers Increased heart size and efficiency

Combination Training Combining maximal resistance training

and aerobic endurance training interferes primarily with muscular strength and power performance

Biochemical Changes Induced by Training Aerobic

Increased myoglobin content Increased oxidation of

glycogen Inc. # & size of

mitochondria Inc. activity of Krebs cycle Inc. muscular stores of

glycogen

Anaerobic Increased capacity of the

ATP-PC system Inc. stores

Increased glycolytic capability

Fiber Type Characteristics

Substrate Depletion and Repletion Phosphagen and ATP

Repletion: work:rest ratio recommendations

Application Divide into equal groups and develop a sport

specific workout. You must address the Aerobic and Anaerobic needs of the Athlete. Assumptions

You are not coaching the athletes you are preparing them physiologically for their sport.

We will assume a total body focus to your anaerobic training…highlight the areas of specific interest pertaining to your athlete.

BE EVIDENCE BASED!

Athlete1) Distance Runner

2) Soccer Midfielder

3) Shot Putter

4) Basketball Forward

5) Baseball Pitcher

6) Swim Sprinter

7) Distance Swimmer

8) Long Jumper