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Detraining is the partial or complete loss of physiological and performance adaptations previously gained through exercise training because the training stimulus has been substantially reduced or stopped. It can occur during periods of injury, illness, inactivity, …
The diaphragm is a dome-shaped sheet of skeletal muscle and tendon that separates the thoracic cavity, containing the lungs and heart, from the abdominal cavity. It forms the floor of the thorax and the roof of …
Dietary fiber is a group of substances that resist digestion and absorption in the human small intestine. It includes nondigestible carbohydrates that are intrinsic and intact in plant foods, together with lignin, a noncarbohydrate component associated …
Dipeptides are peptides composed of two amino-acid residues. In a typical linear dipeptide, the carboxyl group of one amino acid is joined to the amino group of another by a peptide bond. This leaves one amino …
A drop set is a resistance-training technique in which an exercise is typically performed to, or close to, muscular failure, the load is then reduced, and additional repetitions are performed immediately with little or no rest. …
A drop jump is a jumping exercise in which a person drops from an elevated platform, lands, and immediately jumps upward. The initial drop provides a landing impact before the upward effort. In testing, stepping off …
The duodenum is the first and shortest section of the small intestine. It begins at the pylorus, where the stomach empties, and continues to the jejunum at the duodenojejunal junction. In adults, it is roughly 25 …
Dynamic knee valgus is a movement pattern in which the knee moves medially relative to the hip and foot during a weight-bearing task such as squatting, landing, running, or changing direction. Although it is often recognized …
Dynamic stretching is a stretching technique in which joints are moved repeatedly through a controlled range of motion using active muscular contractions, without holding a prolonged position at the end of the movement. The movements are …
Eating disorders involve persistent eating-related symptoms that impair health or functioning, and cannot be identified from body size or one habit alone.
Ecological momentary assessment repeatedly samples experiences close to when they occur in daily life, reducing reliance on long-term recall.
The edible portion is the part of a food counted as edible after material classified as refuse has been removed. In food-composition records, this might mean an apple without its core and stem, or a chicken …
An effector is a cell, tissue, or organ that produces a physiological response when it receives an appropriate signal. In the nervous system, effectors are the targets of motor, or efferent, pathways. Muscles and glands are …
Elastic recoil, in respiratory physiology, is the tendency of the lungs to return toward a smaller volume after they have been expanded during inspiration. As the lungs expand, mechanical energy is stored in lung tissues and …
Emulsification is the process of dispersing one liquid into another liquid with which it does not normally mix. In digestion, the term usually refers to the dispersion of dietary fat into small lipid droplets within the …
The endocannabinoid system uses locally produced lipid messengers and receptors to regulate cell signaling, with effects that vary across tissues.
The endogenous opioid system uses body-made peptides and receptors for diverse signaling roles, with effects shaped by the tissue and neural circuit.
Endurance exercise is physical activity performed continuously or repeatedly over a relatively prolonged period, requiring the body to sustain muscular work over time. Activities such as distance running, cycling, swimming, and prolonged walking are common examples. …
Energy balance is the relationship between the energy a person obtains from food and beverages and the energy the body expends. When energy intake and expenditure are approximately equal over a given period, body energy stores …
Energy compensation describes changes that offset an intended shift in energy balance, with sources and amounts that vary rather than follow a fixed rule.
Energy density measures food energy per gram, distinguishing how concentrated calories are from portion size or the amount of nutrients a food provides.
Energy expenditure is the amount of energy the body uses to maintain physiological functions and perform physical activity. Total daily energy expenditure (TDEE) represents the energy expended over about 24 hours and is commonly described in …
Energy intake measures the energy consumed in foods and drinks, while equal calorie totals can still describe very different nutritional patterns.
Enterocytes are specialized absorptive epithelial cells that line the intestinal surface, particularly the villi of the small intestine. They make up the majority of cells in the small-intestinal epithelium and form a major interface between material …
Enteropeptidase is a digestive serine protease located mainly on the brush border of enterocytes in the duodenum and proximal jejunum. It is also historically called enterokinase. Its principal physiological function is to activate trypsinogen, the inactive …
Environmental and social cues can prompt learned responses when recurring situations become linked to a behavior through repeated experience.
Epinephrine signals through adrenergic receptors to help meet rapid changes in demand, with effects on circulation and fuel supply that differ by tissue.
The esophageal phase is the stage of swallowing in which a swallowed bolus is transported through the esophagus toward the stomach. It follows the pharyngeal phase, during which the bolus passes through the throat and enters …
The Estimated Average Requirement (EAR) is the average daily intake of a nutrient estimated to meet the requirement of 50 percent of healthy people in a particular life-stage and sex group. It is one of the …
Estrogen is a collective term for a group of steroid hormones that produce biological effects through estrogen receptors. The three major naturally occurring estrogens in humans are estradiol (E2), estrone (E1), and estriol (E3). Estradiol has …
Exercise is a form of physical activity that is planned, structured, repetitive, and performed with the purpose of improving or maintaining one or more components of physical fitness. Unlike incidental movement during everyday life, exercise involves …
Exercise prescription is the structured specification of an exercise program designed to achieve particular fitness, health, or functional goals. Rather than simply recommending that a person be more active, an exercise prescription defines how exercise is …
Exercise snacking spreads short purposeful bouts across the day, with physiological effects that depend on the activity and the training dose.
Exercise-induced hypoalgesia describes a temporary reduction in measured pain sensitivity, without guaranteeing relief from an individual's clinical pain.
Exercise-induced muscle damage is disruption of muscle structures and function caused by exercise, particularly unfamiliar or strenuous activity involving eccentric contractions. These are contractions in which an active muscle lengthens under load. The disruption can affect …
The external oblique is a paired skeletal muscle forming the most superficial of the three flat muscle layers of the anterolateral abdominal wall. It lies superficial to the internal oblique and transversus abdominis. The muscle originates …
The extracellular matrix, or ECM, is an organized network of proteins and polysaccharides located outside cells. Cells produce and assemble these molecules into structures that surround, support, and connect cells within tissues. The amount and composition …
FAD and FADH₂ are the oxidized and fully reduced forms of flavin adenine dinucleotide, a redox cofactor used by many enzymes. FAD contains a flavin group derived from riboflavin, or vitamin B2, linked to an adenine …
The FITT principle is a framework used to describe and organize the main components of an exercise prescription. FITT stands for frequency, intensity, time, and type. Together, these variables describe how often exercise is performed, how …
Fascia is connective tissue that forms identifiable sheets or sheaths around and between muscles and other internal structures. In this anatomical sense, it helps attach, enclose, and separate body parts. The term refers to supporting tissue, …
Fast glycolytic fibers are skeletal muscle fibers characterized by fast contractile properties and relatively high glycolytic capacity. In traditional physiological classifications, the term describes fast-twitch fibers with comparatively low oxidative capacity and rapid fatigue. In adult …
Fasting is the voluntary abstinence from some or all food, or from food and beverages, for a defined period. The term covers a range of practices that differ in duration and in whether water or limited …
Fat malabsorption is impaired absorption of dietary fat from the gastrointestinal tract. Normal fat absorption depends on several coordinated steps, including digestion of triglycerides, the action of bile acids, uptake of lipid digestion products by intestinal …
Fat mass estimates the body's fat compartment through a measurement model, without directly mapping fat distribution or giving interchangeable test results.
Fat oxidation is the metabolic process by which fatty acids are broken down and their chemical energy is used to support cellular energy production. In humans, a major pathway involved is mitochondrial fatty acid beta-oxidation. Fatty …
Fat-free mass (FFM) is the component of body mass that remains after fat mass is excluded. In the commonly used two-component model of body composition, total body mass is divided into fat mass and fat-free mass. …
Fatty acids are a class of organic molecules consisting of a hydrocarbon chain with a carboxyl group at one end. Naturally occurring fatty acids commonly have unbranched chains containing an even number of carbon atoms. Because …
Flexibility is a component of physical fitness traditionally related to the range of motion available at a joint or group of joints. It depends particularly on the properties of muscles and other soft tissues surrounding the …
