CHAPTER 4 Bone Muscle and Connective Tissue Adaptation

CHAPTER 4 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

Bone Modeling in Response to Mechanical Loading

Bone Architecture: Cortical and Trabecular Bone

Forces that reach or exceed a threshold stimulus repeatedly initiate new bone formation in the area experiencing the mechanical strain.

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.

Table 4. 1 Exercise Prescription Guidelines for Stimulating Bone Growth Variables Specific recommendations Volume 3 -6 sets of up to 10 repetitions Load 1 -10 RM 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 the magnitude of the load (intensity), rate (speed) of loading, direction of the forces, and volume of loading (number of repetitions).

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.

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

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 jumpers 63%

Formation of a Collagen Fiber

Collagen fiber is the primary structural component of all connective tissue Connective Tissue – tendons, ligaments, fascia, and cartilage Type I collagen makes up the majority of tendon, ligament and bone

Tendons, Ligaments and Fascia Tendons and Ligaments have a direct blood supply, but bone and muscle have a greater blood supply Ligaments contain elastic fibers called elastin in addition to collagen; elastin is extensible Tendons and ligaments attach directly to bone or cartilage; get strong as bone diameters gets bigger Fascia is a fibrous connective tissue that surrounds and separates skeletal muscle; epimysium, perimysium, and endomysium, the epimysium converge to form the tendon

Cartilage Function of Cartilage – See p. 68; cartilage has a poor blood supply Two main types of Cartilage – Hyaline and Fibrous Cartilage is loose packed, has a spring action and lies in an aqueous environment which allow it to take a great deal of force by changing its shape then reforming. Allows for a great deal of compression, ie knee joint and vertebral column

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, an increase in the number of collagen fibrils, and an increase in the packing density of collagen fibrils. --Which all leads to the tendon’s ability to withstand tension forces

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.