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Absolute strength: The maximum force a person can exert with his or her whole body, or part of the body, irrespective of body size or muscle size.

Acceleration: The rate of change in velocity.

Accessory muscles of ventilation: The muscles other than the diaphragm and intercostal muscles that may be used for labored breathing.

Acetylcholine: A neurotransmitter and derivative of choline that is released at the ends of nerve fibers in the somatic and parasympathetic nervous systems, and is involved in the transmission of nerve impulses in the body.

Acetyl-Coenzyme A: A molecule produced from either carbohydrate or free fatty acid catabolism that enters into the Krebs cycle.

Actin: Contractile protein that makes up the thin filament in the sarcomere of a myofibril.

Action potential: The transmission of a nerve impulse along the length of the membrane of a muscle cell or nerve cell due to changes in electrical potential.

Active aging: A concept advanced by the International Council on Active Aging and adopted by the World Health Organization that encourages individuals to be "engaged in life" as fully as possible despite health status, disease conditions, or socioeconomic status. It recognizes the importance of each of the seven dimensions of wellness—physical, intellectual, emotional, spiritual, environmental, vocational, and social—to the overall well-being of an aging individual.

Active isolated stretching (AIS): A technique that blends portions of active and passive stretching that was originally used during rehabilitation for surgery patients.

Active stretching: The process of enhancing the stretch of a muscle by actively contracting its antagonist.

Active system: Consists of the muscular system, and through its action it provides the necessary stiffness to a joint to aid in maintaining its stability.

Activities of daily living (ADL): Activities normally performed for self-care and include personal hygiene (e.g., bathing), performing household chores, walking, shopping, and other similar activities.

Acute altitude sickness: Illness that results from changes in the body's responses to lowered levels of oxygen and air pressure changes.

Acute myocardial infarction: Sudden heart attack.

Adaptability: The ability of an organism to adjust and enhance its ability to tolerate stressors like environmental changes to the demands of exercise.

Adenosine diphosphate (ADP): A molecule that combines with inorganic phosphate to resynthesize adenosine triphosphate (ATP).

Adenosine triphosphate (ATP): Refers to a high-energy phosphate molecule. The breakdown (or hydrolysis) of ATP results in the release of free energy that can be harnessed to support muscle action. The design of cellular metabolism is to maintain ATP and three energy systems exist to regenerate ATP at different maximal rates for differing durations.

Adherence: The extent to which people follow their plans or treatment recommendations, for example, exercise adherence is the extent to which people follow ...

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