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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
1-10RM
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 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
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.