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power that may be translated into motion, overcoming resistance or causing a physical change; the ability to do work. Energy assumes several forms; it may be thermal (in the form of heat), electrical, mechanical, chemical, radiant, or kinetic. In doing work, the energy is changed from one form to one or more other form(s). In these changes some of the energy is “lost” in the sense that it cannot be recaptured and used again. Usually there is loss in the form of heat, which escapes or is dissipated unused; all energy changes give off a certain amount of heat.ƒ

All activities of the body require energy, and all needs are met by the consumption of food containing energy in chemical form. The human diet comprises three main sources of energy: carbohydrates, proteins, and fats. Of these three, carbohydrates most readily provide the kind of energy needed to activate muscles. Proteins work to build and restore body tissues. The body transforms chemical energy derived from food by the process of metabolism, an activity that takes place in the individual cell. Molecules of the food substances providing energy pass through the cell wall. Inside the cell, chemical reactions occur that produce the new forms of energy and yield by-products such as water and waste materials; see also adenosine triphosphate.
free energy (Gibbs free energy (G)) the energy equal to the maximum amount of work that can be obtained from a process occurring under conditions of fixed temperature and pressure.
nuclear energy energy that can be liberated by changes in the nucleus of an atom (as by fission of a heavy nucleus or by fusion of light nuclei into heavier ones with accompanying loss of mass).
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

en·er·gy (E),

The exertion of power; the capacity to do work, taking the forms of kinetic energy, potential energy, chemical energy, electrical energy, etc.
Synonym(s): dynamic force
[G. energeia, fr. en, in, + ergon, work]
Farlex Partner Medical Dictionary © Farlex 2012


The capacity to do work, measured in joules Types Potential/stored energy, kinetic/in motion energy. See Activation energy, Adaptation energy, Binding energy, Biomass energy, Bond dissociation energy, Department of Energy, Orgone energy.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.


(E) (en'ĕr-jē)
The exertion of power; the capacity to do work, taking the forms of kinetic energy, potential energy, chemical energy, electrical energy, and other types.
[G. energeia, fr. en, in, + ergon, work]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


The capacity of a body to do work. Energy occurs in several forms-potential as in a compressed spring or a mass in a high position, kinetic as in motion, chemical as in petroleum and nuclear as in the binding forces of the atomic nucleus. Its effect, when manifested, is to bring about a change of some kind. The term is also used metaphorically to refer to human vitality and appetite for exertion or work.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005


the capacity of a body or system to do work. The most important energy forms, as far as living organisms are concerned, are heat, radiant, chemical and mechanical energy. Energy units of importance are:

The quantity of solar energy entering the earth's atmosphere is 64.3×108 J m-2 yr-1. The amount of solar energy available to plants in Britain is 10.5×108 J m-2 yr-1. The SI UNIT of energy is the joule (J). In plants and animals, energy is stored in ATP (short-term storage), and starch and FAT (long-term storage).

Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005


Exertion of power; capacity to do work.
[G. energeia, fr. en, in, + ergon, work]
Medical Dictionary for the Dental Professions © Farlex 2012

Patient discussion about energy

Q. Is energy drinks really boost my energy? Now-a-days the sale of the energy drinks have grown high. Is energy drinks really boost my energy?

A. People have a mind set that energy drinks really boost them to do work or to relax more. Actually energy drinks may give you a temporary energy boost. The "boost" typically comes from the large amount of sugar and caffeine these drinks contain. Although the various sugars used to sweeten energy drinks can briefly increase energy, consuming large quantities of sugar is likely to cause weight gain. Caffeine is a stimulant, which also can temporarily perk you up. But too much caffeine can cause adverse side effects, such as nervousness, irritability, increased heart rate and blood pressure, and insomnia.

Energy drinks are not necessarily bad for your health. But you shouldn't see them as some "natural" energy boost — the boost they give is from caffeine. Some of the claims made by manufacturers of energy drinks — such as "improves performance and increases concentration" — can be misleading.
Consider a better way to boost your energy: Get adequate sleep,


A. Not really my area, but you can try and ask in the alternative medicine community (

You can read about these things here:,

Q. I suffer of lack in energy lately, any advice? I’m 35, usually a strong guy but for the past 3 weeks I’ve been sleeping all day, doing nothing while awake, having no energy to do anything. Any one know a reason or what should I do?

A. Have you tried changing your diet? You may lack of vitamins or other essential materials that can cause drowsiness. Try eating vegetables and fruits. Force yourself to do a daily walk, 25 minutes, that’s all. and could be you got an infection that will take some time…

More discussions about energy
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