NSCA’s Essentials of Personal Training (Third Edition) – Chapter 1-16 - Terms & Definitions
made by Geraldine van Essen – Nutrition and Health Promotion - Personal Trainer – 2024
Chapter 1 – Structure and Function of the Muscular, Nervous, and Skeletal Systems:
- Muscle contraction / Muscle action: Muscles generate force when they are activated
- Epimysium: A layer of connective tissue that surrounds a skeletal muscle
- Muscle fibers / Fasciculus / Fascicle: A bundle that is a division of a (skeletal) muscle
- Perimysium: A layer of connective tissue that surrounds a fasciculus
- Endomysium: A layer of connective tissue that surrounds and separates a muscle fiber from other
adjacent fibers within a fasciculus
- Sarcolemma: A plasma membrane that surrounds a muscle fiber → Encloses the contents of the cell,
regulates the passage of materials such as glucose into and out of the cell, and receives and conducts
stimuli in the form of electrical impulses
- Action potentials: Electrical impulses
- Cytoplasm / Sarcoplasm: A watery solution within the boundary of the sarcolemma, but outside the
nuclei, which contains the cell’s energy sources, such as ATP, phosphocreatine, glycogen, and fat
droplets
- Adenosine triphosphate (ATP): The only direct source of energy for muscle actions
- Mitochondria: The sites of aerobic ATP production within the cell
- Sarcoplasmic reticulum: An organelle that stores calcium and regulates the muscle action process by
altering the intracellular calcium concentration
- Transverse tubules / T-tubules: Channels that form openings in the sarcolemma of the muscle cell
- Myofibrils: Columnar protein structures that run parallel to the length of the muscle fiber
- Myofilaments: Each myofibril is a bundle of myofilaments, which primarily consist of myosin (thick)
and actin (thin) filaments
- Myosin (contractile protein): The thick myofilament inside a muscle fiber, which is formed from the
aggregation of myosin molecules, which consist of a head, neck, and tail. The head is capable of
attaching to and pulling on an actin filament
- Actin (contractile protein): The thin myofilament inside a muscle fiber, which is formed from individual
globular (G-actin) proteins. Each G-actin has a binding site for a myosin head
- Tropomyosin (regulatory protein): A rod-like protein that spans the length of seven G-actin proteins
along the length of an actin filament
- Troponin (regulatory protein): Binding site for calcium ions → Causes the movement of tropomyosin
away from the myosin binding sites on actin
- Nebulin: A protein that acts to ensure the actin filaments are the correct length
- Sarcomere: The basic contractile unit of a muscle → Extends from one Z-line to an adjacent Z-line
- A-band: Determined by the width of a myosin filament → Provides the dark striation of skeletal muscle
- H-zone: The area of the A-band that contains myosin but not actin
- M-line: A dark line in the middle of the H-zone → Helps align adjacent myosin filaments
,- I-band: Spans the distance between the ends of adjacent myosin filaments. Each I-band lies partly in
each of two sarcomeres → Responsible for giving skeletal muscle its light striation
- Neuromuscular junction: A specialized region for a nervous and muscle system where
communication occurs and where muscle fibers receive a stimulus from the nervous system. Each
muscle fiber has a single neuromuscular junction
- Motor endplate: The axon terminal of a neuron → A specialized region of the muscle cell membrane
- Synaptic cleft / Neuromuscular cleft: The space between the axon terminal and motor endplate
- Sliding filament theory:
1. An action potential passes along the length of a neuron, which leads to the release of the excitatory
neurotransmitter acetylcholine (ACh) at the neuromuscular junction. In rest, ACh is stored in synaptic
vesicles inside the axon terminal of the neuron. The action potential leads to the release of stored ACh
into the synaptic cleft between the axon terminal of the neuron and the muscle fiber
2. ACh migrates across the synaptic cleft and binds with ACh receptors on the motor endplate of the
muscle fiber
3. An action potential is generated along the sarcolemma of the muscle fiber, and it will travel to the
interior of the muscle fiber via T-tubules. This triggers the release of stored calcium from the
sarcoplasmic reticulum
4. Calcium migrates to, and binds with, troponin molecules located along the length of the actin
filaments
5. This causes a conformational change in the shape of troponin. The bound tropomyosin to troponin
moves such that the binding sites on actin are exposed to the myosin head
6. In a resting state, the myosin head is ‘’energized’’ (storing energy released from the
dephosphorylation of ATP). When the myosin head attaches to the actin binding sites, crossbridges are
formed and the actin filament is pulled towards the center of the sarcomere. Whether it is successful at
, pulling and thus shortening the muscle, depends on the amount of force generated by the crossbridges
that are pulling and the external force that opposes the crossbridges
7. After pulling on the actin filament, the myosin head is now in a lower energy state. A fresh ATP
molecule must be bound to cause detachment from the actin filament, as well as to energize the
myosin head. Once ATP is bound, the myosin head detaches from the actin, and the enzyme myosin
adenosine triphosphatase (ATPase) causes the splitting of the ATP molecule. This energizes the
myosin head again. This process will continue provided that the muscle fiber is being stimulated to
contract by its motor neuron
- Concentric muscle action: The amount of force produced by a muscle is greater than the external
resistance acting in the opposite direction. The resistance is overcome, and the muscle shortens
- Eccentric muscle action: The amount of force produced by a muscle is less than an opposing external
resistance. The muscle will lengthen even as it attempts to shorten
- Isometric (static) muscle action: The muscle force is equal and opposite to that of an external
resistance. The muscle neither shortens nor lengthens, but remains the same length
- Delayed-Onset Muscle Soreness (DOMS): Muscular pain and discomfort 24 to 48 hours after
beginning an exercise program or performing novel exercises, caused by a combination of connective
and muscle tissue damaged followed by an inflammatory reaction that activates pain receptors. The
damage is primarily caused by eccentric muscle action
- Oxidative capacity: The ability of a muscle fiber to produce ATP aerobically
- Oxidative fibers: Fibers that have large and numerous mitochondria, and that are surrounded by an
ample supply of capillaries to deliver blood and oxygen
- Myoglobin: A protein that is possessed by oxidative fibers in a large amount, which delivers oxygen from
the muscle cell membrane to the mitochondria, enhancing aerobic capacity and lessening the reliance
on anaerobic ATP production
- Specific tension: Fibers that differ in the amount of force they produce relative to their size (cross-
sectional area)
- Type I muscle fibers: Slow oxidative (SO), or slow-twitch fibers → High oxidative capacity and fatigue
resistant, but contract and relax slowly
- Type IIa muscle fibers: Fast oxidative glycolytic (FOG) fibers → Moderate to high anaerobic capacity
and somewhat fatigue resistance
- Type IIx muscle fibers: Fast glycolytic (FG) fibers → Purely anaerobic and highly fatigable
, - Central nervous system: Consists of the brain and spinal cord
- Peripheral nervous system: Lies outside the central nervous system and may be further divides into
motor (efferent) and sensory (afferent) divisions
- Motor (efferent): Relays nerve impulses from the CNS to the PNS (e.g., to skeletal muscles)
- Sensory (afferent): Relays nerve impulses from the PNS to the CNS
- Somatic (voluntary) nervous system: Responsible for activating skeletal muscles (e.g., the rhythmic
actions of the quadriceps femoris muscles during cycling)
- Autonomic (involuntary) nervous system: Controls involuntary functions (e.g., contraction of the
heart, smooth muscle in blood vessels, glands)
- Sympathetic nervous system: A fight-flight response → Branch from the autonomic nervous system
that supports the muscle actions initiated by the somatic nervous system (e.g., increased blood flow
from the heart, greater ventilation of the lungs, redistribution of blood flow to the skeletal muscles,
increased sweating)
- Parasympathetic nervous system: Active during rest → Branch from the autonomic nervous system
that is responsible for processes such as digestion, urination, and gland secretion
- Neuron: A nerve cell → The most basic unit of the nervous system
- Motor neurons / Efferent neurons: Motor signals that cause skeletal muscles to contract → Conduct
impulses from the CNS to the muscles
- Sensory neurons / Afferent neurons: Carry impulses from the PNS to the CNS → Relay impulses from
the PNS to the CNS regarding information such as tension, stretch, movement, and pain
- Synapse: The site of communication between two neurons or a neuron and a gland or muscle cell
- Dendrites: Projections from the neuron cell body → Receive excitatory or inhibitory signals (or both)
from other neurons. Both the dendrites and the cell body of a motor neuron are located in the anterior
gray horn of the spinal cord
- Muscle spindle: A spindle-shaped sensory organ/stretch receptor that is widely dispersed throughout
most skeletal muscles → Specialized to sense changes in muscle length
- Extrafusal fibers: Ordinary skeletal muscle fibers outside the muscle spindle
- Intrafusal fibers: Specialized muscle fibers inside the muscle spindle → Have contractile proteins at
each end (actin and myosin) and a central region that is wrapped by sensory nerve endings
- Myotatic / Stretch reflex: A motor response (reflex) which activates the muscle that is initially
stretched
- Golgi tendon organ: Located at the junction of the muscle and tendon that attaches the muscle to the
bone → Plays a role in protecting the muscle from injury by relaxing the acting muscle and stimulating
the antagonist muscle
