NASM essentials of sports performance training
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NASM essentials of sports performance training


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events of contraction, the fiber will contract
completely. The amount of force generated by the whole muscle is dictated by a number of fac-
tors including the number of fibers recruited, the rate at which the central nervous system (CNS)
stimulates the neuron, and the fibers the neuron controls.
CONNECTIVE TISSUE
Connective tissue has multiple functional categories:
\u2022 Enclose and separate tissues
\u2022 Connect dissimilar tissues
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\u2022 Support and movement
\u2022 Energy storage
\u2022 Cushion and insulate
\u2022 Transport
\u2022 Protection
The protective coverings around most tissues, including muscle fibers, are made up of connective
tissue. The basic structure of connective tissue is illustrated in Figure 4.6. Connective tissue is
composed of two types of protein-based fibers; collagenous and elastic fibers (26\u201329). Collage-
nous fibers are composed mainly of strong, inelastic collagen, one of the most common proteins
in the body. Elastic fibers contain elastin, a highly extensible protein capable of stretch and com-
pression that then can return to its initial length. Connective tissues of importance to flexibility
and the musculoskeletal system include tendons (connects muscle to bone), ligaments (connects
bone to bone), and fascia. Fascia binds muscles into separate groups. There are three layers to the
fascial sheaths, according to the structures which they surround: endomysium (endo-: within);
perimysium (peri-: around); epimysium (epi-: on). 
Endomysium is the innermost fascial layer that encases individual muscle fibers. The sheath
that binds groups of muscle fibers into fasciculi is called perimysium. The outermost layer of the
muscle fiber is the epimysium. This layer binds entire fascicles together (1,29). These connective
tissues must also respond to flexibility training for permanent change (i.e., plastic deformation)
to occur. Overuse injuries initiate the cumulative injury cycle (Fig. 4.2), which stimulates the de-
velopment of inelastic, fibrous adhesions (30). These adhesions form in the connective tissue
within layers of muscle. This prevents normal muscle mechanics and normal soft-tissue extensi-
bility (31).
All tissues contribute to joint stiffness to varying degrees. Joint capsules and ligaments rep-
resent 47% of joint stiffness followed by muscle fascia (41%), tendons (10%), and skin (2%) (32).
Although the myofascial system is ranked second, this tissue is a primary focus of a flexibility rou-
tine. Tissue properties of the muscle and fascia allow for greater elasticity and a greater adaptive
potential than ligamentous tissue. Furthermore, tendons are biologically designed to transmit
tension to the skeleton, so elasticity would be counter to its primary function. Overstretching lig-
aments can produce unstable joints. Unstable joints can alter the normal length-tension rela-
tionships, force-couple relationships, and joint arthrokinematics, leading to synergistic domi-
nance and faulty movement patterns leading to the cumulative injury cycle by placing unwanted
stress on the entire human movement system (19). Sports Performance Professionals must keep
in mind that myofascial, neural, and vascular structures incur stress as a result of an applied
stretch, so an integrated flexibility training program must be designed accordingly.
NEURODYNAMICS
All neural tissue has to adapt to constantly changing joint angles and alterations in the position
of the adjacent tissue. Muscle imbalances, joint dysfunctions, and postural distortions place ab-
normal tension on the neural tissues. This affects the structural integrity of the neural structures
and leads to abnormal neurodynamics (33). 
REVIEW OF THE NEUROANATOMY OF 
THE PERIPHERAL NERVOUS SYSTEM
The CNS is made up of the brain and spinal cord; portions of the overall nervous system that are
contained within bone and meninges. The peripheral nervous system (PNS) is external to the
CNS and includes the spinal nerves, sensory receptors, nerves, ganglia, and plexuses (Fig. 4.7)
(21,23). Primary divisions of the PNS include the sensory division (takes information from the
peripheral sensory receptors to the CNS) or the motor division (information from the CNS to ef-
fector organs). The motor division is further divided into the somatic nervous system (informa-
tion from the CNS to skeletal muscle) and the autonomic nervous system (information from the
CNS to smooth muscle, cardiac muscle, and some glands). Finally, the autonomic nervous sys-
tem is divided into the sympathetic nervous system (prepares body for activity) and the parasym-
pathetic nervous system (controls resting and vegetative functions). The enteric nervous system
controls the digestive tract. 
The functional unit of the nervous system is a neuron. Bundles of neurons make up a nerve
and are surrounded by the endoneurium, perineurium, epineurium, and mesonerium (Fig. 4.8)
(33,34). These connective tissue structures form a tough supporting framework for the contained
neuron (33\u201336). The neural connective tissues are self-innervated by the Nervi nervorum
(33\u201335). This innervation, along with an abundant blood supply, makes the connective tissue of
the nerve very reactive and pain sensitive (33\u201335). 
126 CHAPTER 4
Endomysium
The innermost fascial
layer that encases individual
muscle fibers.
Perimysium
The sheath that binds
groups of muscle fibers into 
fasciculi.
Epimysium
The outermost layer of
a muscle fiber.
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FLEXIBILITY TRAINING FOR PERFORMANCE ENHANCEMENT 127
Posterior view
Central
nervous
system Spinal
cord
Brain
Spinal
nerves
Peripheral
nervous
system
Cranial
nerves
FIGURE 4.7 The peripheral nervous system.
Perineurium
Epineurium
FIGURE 4.8 Neural connec-
tive tissue.
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128 CHAPTER 4
Stimulated
nociceptors
Pain
Tissue
trauma
Intraneural
edema
Chemical
irritation
Tissue
hypoxia
Microvascular
stasis
FIGURE 4.9 Neuropathophysiology.
TABLE 4.3
Effects of Aging
1. Muscular atrophy
2. Neural atrophy
3. Connective tissue hypertrophy
4. Increased tissue stiffness
5. Tissue dehydration
Atrophy
The loss in muscle 
fiber size.
Sarcopenia
A decrease in muscle
fiber numbers.
Neuropathophysiology 
The integrity of neural tissue can be compromised by acute injury (compression), chronic injury
(repetitive microtrauma), muscle imbalances, joint dysfunctions, and poor posture (Fig. 4.9)
(27,33,37). Tissue trauma initiates a neurogenic reflex mechanism, the cumulative injury cycle,
and creates morphological changes in the microenvironment of the neural tissue resulting in in-
traneural edema, chemical irritation, tissue hypoxia, and microvascular stasis (28,29,32,33,
38\u201340). These alterations stimulate the nociceptors and result in pain, causing protective muscle
microspasms that decrease the provocation to the inflamed neural tissues (34,41,42). These mi-
crospasms alter length-tension relationships, force-couple relationships, and joint arthrokine-
matics, further altering movement patterns. This process eventually leads to intraneural fibrosis
and decreased neural tissue elasticity (34,42,43), and prevents normal neurodynamics during
functional movements, and further perpetuates the dysfunctional cycle (34,36,43,44).
FACTORS LIMITING FLEXIBILITY 
Factors that limit flexibility vary on an individual basis. Aging and immobilization are two limit-
ing factors important to the Sports Performance Professional. 
EFFECTS OF AGING
The body\u2019s ability to remain flexible is reduced through the natural process of aging. Physical
changes attributed to aging that affect flexibility include muscular and neural atrophy, connec-
tive tissue hypertrophy, increased