4 4 C H A P T E R 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

© 2007 McGraw-Hill Higher Education. All rights reserved. 1-4 Bone Properties Bone size & shape are influenced by the direction & magnitude of forces that are habitually applied to them Bone size & shape are influenced by the direction & magnitude of forces that are habitually applied to them Bones reshape themselves based upon the stresses placed upon them Bones reshape themselves based upon the stresses placed upon them Bone mass increases over time with increased stress Bone mass increases over time with increased stress

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 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

© 2007 McGraw-Hill Higher Education. All rights reserved. 1-8 Bone Properties Composed of calcium carbonate, calcium phosphate, collagen, & water Composed of calcium carbonate, calcium phosphate, collagen, & water 60-70% of bone weight - calcium carbonate & calcium phosphate 60-70% of bone weight - calcium carbonate & calcium phosphate 25-30% of bone weight - water 25-30% of bone weight - water Collagen provides some flexibility & strength in resisting tension Collagen provides some flexibility & strength in resisting tension Aging causes progressive loss of collagen & increases brittleness Aging causes progressive loss of collagen & increases brittleness

© 2007 McGraw-Hill Higher Education. All rights reserved. 1-9 Bone Properties Most outer bone is cortical with cancellous underneath Most outer bone is cortical with cancellous underneath Cortical bone – low porosity, 5 to 30% nonmineralized tissue Cortical bone – low porosity, 5 to 30% nonmineralized tissue Cancellous – spongy, high porosity, 30 to 90% Cancellous – spongy, high porosity, 30 to 90% Cortical is stiffer & can withstand greater stress, but less strain than cancellous Cortical is stiffer & can withstand greater stress, but less strain than cancellous Cancellous is spongier & can undergo greater strain before fracturing Cancellous is spongier & can undergo greater strain 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 VariablesSpecific recommendations Volume3-6 sets of up to 10 repetitions Load1-10RM Rest1-4 min VariationTypical periodization schemes designed to increase muscle strength and size Exercise selectionStructural exercises: squats, cleans, deadlifts, bench presses, shoulder presses

T he 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. 

S pecific 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 % Sedentary Controls 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 Affect Adaptations to Training Environmental factors Climate Altitude Genetic endowment Fiber type patterns Somatotype

Adaptations Following Exercise 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 Following Exercise 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 athleteType II fibers Bodybuilders44% Javelin throwers50% 800-m runners52% Weightlifters60% Shot-putters62% Discus throwers63% 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 from Aerobic 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!

Athlete 1) Distance Runner 2) Soccer Midfielder 3) Shot Putter 4) Basketball Forward 5) Baseball Pitcher 6) Swim Sprinter 7) Distance Swimmer 8) Long Jumper

Bone is designed to strain between under normal loads. Whenever there is a mis- match between the genetically expected strain and the actual strain adaptive remodeling will occur. It is believed that the osteocytes are the sensors of bone strain. The osteocytes can communicate directly with the osteoblast. When new bone is needed the osteocytes inform the osteoblast to become active and lay down new bone. When below normal strains are observed the osteocytes send a bone resorption stimulus to the osteoclast via the osteoblast. [From Rubin #1880] Adaptive Remodeling of Bone

F orces that reach or exceed a threshold stimulus initiate new bone formation in the area experiencing the mechanical strain.  Minimal Essential Strain (MES) refers to the threshold stimulus that initiates new bone formation.

Stimulating Bone Formation  Use exercises that directly load particular regions.  Use structural exercises.  Progressively overload the musculoskeletal system, and progressively increase the load.  Vary exercise selection.

T he 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. 

Table 4.2 Proportion of Type II Fibers in Athletes Who Perform Anaerobic Activities Type of athleteType II fibers Bodybuilders44% Javelin throwers50% 800-m runners52% Weightlifters60% Shot-putters62% Discus throwers63% Sprinters and 63% jumpers

Formation of a Collagen Fiber