Resistance Training Principles, Adaptations, and Flexibility

Comprehensive vocabulary flashcards covering the physiological mechanisms, adaptations, and prescription parameters for muscular strength, power, endurance, hypertrophy, and flexibility.

Muscular Hypertrophy

An increase in the overall size of muscle fibers (cells), characterized by an increased quantity of contractile proteins, an increased number and size of myofibrils, more connective tissue, and a greater amount of metabolic enzymes.

Muscular Hyperplasia

An increase in the total number of individual muscle fibers (cells); documented in animal models (such as cats and rats) under extreme loading, but with little research supporting its occurrence in humans.

Myofibrillar Hypertrophy

An increase in the volume of muscle fibers driven specifically by the accretion of contractile myofibrils and contractile proteins, directly enhancing the muscle's maximal force-producing capacity.

Sarcoplasmic Hypertrophy

An enlargement of the non-contractile cellular components of muscle fibers, including increased sarcoplasm volume, glycogen storage, and fluid, without an equivalent increase in contractile proteins or force production.

Mechanotransduction

The biological process by which muscle cells detect mechanical perturbations and tension applied to structural proteins and convert them into intracellular biochemical anabolic signals.

mTOR (Mechanistic/Mammalian Target of Rapamycin)

A master regulatory protein kinase triggered by mechanical tension, dietary amino acids, and growth factors that activates downstream signaling ($\text{S6K1}$, $\text{4EBP1}$) to enhance mRNA translation efficiency and ribosomal capacity for protein synthesis.

Muscular Strength

The maximal amount of force that a muscle or muscle group can generate at a specified velocity, typically measured as a one-repetition maximum ($1\text{RM}$).

Muscular Power

The rate of performing work or developing maximal force, defined mathematically as $\text{Power} = \text{Force} \times \text{Velocity}$, with peak values typically achieved at intermediate velocities and moderate external loads.

Motor Unit

The basic functional unit of the neuromuscular system, consisting of an individual alpha motor neuron and all the specific skeletal muscle fibers that it innervates.

Henneman's Size Principle

The neuromuscular rule stating that motor units are recruited in order of increasing size and threshold, such that small, fatigue-resistant Type I motor units are activated before larger, higher-threshold Type II units.

Rate Coding

The firing frequency of action potential discharges delivered by a motor neuron to its innervated muscle fibers, serving as a primary neural mechanism to grade and increase force production.

Force-Velocity Relationship

The inverse physiological relationship in concentric muscle action showing that as shortening velocity increases, the maximal force the muscle can generate decreases.

Muscular Pennation

The architectural arrangement of muscle fibers relative to the line of action; forms include fusiform, unipennate, bipennate, and multipennate, which modulate physiological cross-sectional area and maximal shortening velocity.

Muscular Endurance

The capacity of a muscle or muscle group to sustain repeated contractions or maintain force output against submaximal resistance over an extended period (typically activities lasting $>90\text{ s}$).

Motor Unit Rotation

The neuromuscular strategy used during prolonged submaximal or postural isometric contractions in which some active motor units temporarily deactivate while others are recruited to sustain total force and delay fatigue.

Excitation-Contraction Coupling (ECC) Failure

A peripheral fatigue mechanism characterized by an impaired capability of the action potential along the sarcolemma and transverse tubules to elicit adequate $Ca^{2+}$ release from the sarcoplasmic reticulum.

Satellite Cells

Dormant myogenic stem cells located beneath the basal lamina of muscle fibers that activate, proliferate, and donate myonuclei to damaged fibers to facilitate protein synthesis, repair, and muscle growth.

Metabolic Stress

A stimulus for muscle growth characterized by the accumulation of metabolites (such as $H^+$, $P_i$, and lactate) from anaerobic glycolysis during exercise, leading to cell swelling and anabolic signaling.

Flexibility

The intrinsic ability of a joint to move through a complete, pain-free range of motion without active muscle engagement, reflecting passive tissue extensibility.

Mobility

A functional capability combining available joint range of motion with the motor control, strength, and neuromuscular coordination required to actively move through that range.

Muscle Spindle

A specialized mechanosensory receptor embedded within the intrafusal fibers of skeletal muscle that monitors both the magnitude of change in muscle length and the rate of stretch.

Stretch Reflex

A protective monosynaptic neural reflex initiated by muscle spindle excitation that triggers immediate, involuntary contraction of the stretched muscle to resist further rapid lengthening.

Golgi Tendon Organ (GTO)

A proprioceptive sensory receptor located at the musculotendinous junction that detects changes in tension generated by active muscular contraction or passive stretching.

Autogenic Inhibition

A protective reflex mechanism mediated by Golgi tendon organs whereby excessive or prolonged tension in a muscle causes reflex relaxation of that same muscle.

Stretch Tolerance

A central nervous system adaptation in which repeated stretching alters perception and pain thresholds, allowing an individual to tolerate greater elongation and passive tension before invoking protective resistance.

Proprioceptive Neuromuscular Facilitation (PNF)

Advanced stretching methods that combine passive stretching with voluntary isometric or concentric muscle contractions to facilitate neuromuscular relaxation via autogenic and reciprocal inhibition.

Hold-Relax Technique

A PNF stretching method consisting of a passive stretch ($10\text{--}15\text{ s}$), followed by a submaximal isometric contraction ($6\text{--}10\text{ s}$) of the target muscle, a brief relaxation ($2\text{--}3\text{ s}$), and a deeper passive stretch ($10\text{--}15\text{ s}$).

Contract-Relax-Agonist-Contract (CRAC)

A PNF stretching variant that combines autogenic inhibition (from contracting the target muscle) and reciprocal inhibition (by actively contracting the opposing agonist muscle) to achieve a deeper joint range of motion.