Skeletal Muscle Physiology and Resistance Training Adaptations

Comprehensive vocabulary flashcards covering the structure, microanatomy, excitation-contraction coupling, neural adaptations, fiber type characteristics, and molecular signaling mechanisms of skeletal muscle from Chapters 8 and 14.

Muscular Strength

The maximal force that a muscle group can generate.

Muscular Endurance

The ability of a muscle or muscle group to perform repeated contractions against a submaximal load.

Muscle Hypertrophy

An increase in muscle mass primarily driven by an increase in the cross-sectional area of individual muscle fibers through the accumulation of actin and myosin contractile proteins.

Muscle Power

The rate of performing work, mathematically defined as force times shortening velocity ($\text{Power} = F \times V$).

Cross-Education

The neurological phenomenon in which resistance training of one limb produces measurable increases in strength in the contralateral untrained limb.

Neural Drive

The magnitude of the efferent neural output transmitted from the central nervous system to active muscle fibers.

Mechanistic Target of Rapamycin (mTOR)

A major downstream protein kinase that acts as the master regulator accelerating skeletal muscle protein synthesis following resistance exercise.

Phosphatidic Acid (PA)

A lipid second messenger synthesized by sarcolemmal mechanoreceptors during muscle contractions that directly promotes the activation of mTOR.

Ras Homolog Enriched in Brain (Rheb)

A signaling protein that directly activates mTOR when released from the inhibitory action of TSC2 via contraction-induced Erk activation.

Leucine

A branched-chain amino acid that stimulates a transient increase in muscle protein synthesis independent of resistance exercise, though long-term supplementation alone does not induce hypertrophy in sedentary individuals.

Myonuclear Domain

The volume of cytoplasm surrounding and supported by a single myonucleus within a muscle fiber.

Satellite Cells

Undifferentiated muscle stem cells that proliferate and donate additional nuclei to growing or repairing muscle fibers, maintaining the myonuclear domain during hypertrophy.

Muscle Memory

The physiological mechanism enabling rapid recovery of muscle size and strength upon retraining, mediated by the persistence of training-induced myonuclei that are retained during detraining.

Type IIX Overshoot

A transient elevation of fast-twitch Type IIX fiber percentage above baseline values that occurs during periods of detraining or tapering.

Hyperplasia

An increase in total skeletal muscle mass resulting from an increase in the actual number of individual muscle fibers.

Concurrent Training Interference

The impairment of strength and hypertrophy adaptations when high-volume or high-frequency endurance exercise is performed concurrently with resistance training, mediated in part by AMPK inhibition of mTOR.

Epimysium

The outermost sheath of dense connective tissue surrounding an entire skeletal muscle.

Perimysium

The connective tissue layer that groups individual muscle fibers into discrete bundles termed fascicles.

Fascicle

A distinct bundle of skeletal muscle fibers encapsulated by the perimysium.

Endomysium

The fine layer of connective tissue that encases each individual skeletal muscle fiber.

Sarcolemma

The specialized cell membrane surrounding a skeletal muscle fiber, located directly beneath the basement membrane.

Myofibrils

Elongated contractile thread-like structures within muscle fibers that contain the protein myofilaments actin and myosin.

Sarcomere

The basic functional contractile unit of a muscle myofibril, defined as the region between two adjacent Z lines.

Sarcoplasmic Reticulum (SR)

A network of specialized endoplasmic reticulum channels within muscle fibers that stores and releases calcium ions ($\text{Ca}^{2+}$) necessary for muscle contraction.

Transverse Tubules (T-Tubules)

Invaginations of the sarcolemma that project deep into the interior of the muscle fiber to conduct action potentials toward the sarcoplasmic reticulum.

Neuromuscular Junction (NMJ)

The specialized anatomical synapse where the terminal axon of a motor neuron meets the motor end plate of a muscle fiber.

Motor End Plate

The specialized, folded region of the sarcolemma directly beneath the terminal axonal branch of a motor neuron at the neuromuscular junction.

End-Plate Potential (EPP)

The graded electrical depolarization of the motor end plate induced by acetylcholine binding, which triggers a muscle action potential upon exceeding threshold.

Sliding Filament Model

The process of muscle shortening whereby actin thin filaments slide past myosin thick filaments, resulting in cross-bridge cycling and narrowing of the distance between Z discs.

Troponin

A regulatory protein complex bound to actin that binds calcium ions, initiating a conformational shift that shifts tropomyosin away from actin binding sites.

Tropomyosin

A filamentous protein lying along the grooves of actin that blocks myosin-binding sites in resting muscle to prevent cross-bridge formation.

Myosin ATPase

An enzyme located on the globular myosin head that hydrolyzes ATP into ADP and inorganic phosphate, providing the energy required for the cross-bridge power stroke.

Muscle Fatigue

A reversible reduction in muscle power output characterized by decreased force generation at the cross-bridge level and reduced shortening velocity.

Exercise-Associated Muscle Cramps (EAMC)

Spasmodic, involuntary contractions of skeletal muscle resulting primarily from altered neuromuscular control, involving hyperactive motor neurons, increased muscle spindle activity, and reduced Golgi tendon organ inhibition.

Transient Receptor Potential (TRP) Channels

Sensory nerve ion channels stimulated by pungent dietary compounds (such as ginger and capsaicin) that activate reflexive inhibitory neural pathways to suppress cramping motor neurons.

Type I Muscle Fibers

Slow-twitch muscle fibers possessing high mitochondrial density, high fatigue resistance, aerobic energy reliance, low Vmax, and high energetic efficiency.

Type IIa Muscle Fibers

Intermediate fast-twitch fibers demonstrating moderate-to-high mitochondrial density, high ATPase activity, high shortening velocity, and combination aerobic/anaerobic capacity.

Type IIx Muscle Fibers

Fast-twitch glycolytic fibers displaying low mitochondrial density, low fatigue resistance, predominantly anaerobic energy reliance, highest ATPase activity, and highest shortening velocity (Vmax).

Concentric Contraction

A dynamic muscle action in which internal muscular force exceeds external resistance, causing the muscle to shorten.

Eccentric Contraction

A dynamic muscle action in which external resistance exceeds the force produced by the muscle, causing controlled lengthening under tension.

Isometric Contraction

A static muscle action during which tension is produced without any change in overall muscle length or joint angle.

Summation

The additive buildup of muscular tension resulting from high-frequency electrical stimuli arriving before preceding twitches have completely relaxed.

Tetanus

A smooth, sustained maximal muscular contraction achieved when the frequency of motor neuron stimulation is rapid enough that individual muscle twitches fuse completely.

Sarcopenia

The involuntary, age-related loss of skeletal muscle mass and functional strength, characterized by a selective loss of fast-twitch fibers.

Force-Velocity Relationship

The mechanical principle stating that muscle force generation decreases as shortening velocity increases, with peak velocity occurring at minimal load and peak force occurring at zero velocity.