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

Bone Modeling in Response to Mechanical Loading

Bone Architecture: Cortical and Trabecular Bone

F orces 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 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 the magnitude of the load (intensity), rate (speed) of loading, direction of the forces, and volume of loading (number of repetitions). 

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. 

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 athleteType II fibers Bodybuilders44% Javelin throwers50% 800-m runners52% Weightlifters60% Shot-putters62% Discus throwers63% Sprinters and 63% jumpers

Formation of a Collagen Fiber

Collagen  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. 

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,  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.