In human thermodynamics, exosomatic energy, as contrasted with endosomatic energy (bodily metabolism), is the useful energy throughput outside human bodies. [1]

To elaborate, using the model given by Romanian mathematical economist Nicholas Georgescu-Roegen, if the beak of a bird that kills its prey is an endosomatic instrument, and the energy of the organs and muscles that power the movement of the beak are classified as endosomatic metabolism, then by extrapolation of this model the bow and arrow (or large boat, etc.) that early humans used to kill their prey are thus classified as exosomatic instruments and the structures, such as boat engines or gun powder, that power the movement of the human exosomatic instruments are thus classified as having an abstract type of exosomatic metabolism with an associated "exosomatic energy."

Etymology
The term “exosomatic” was introduced into economics by Romanian mathematical economist Nicholas Georgescu-Roegen in 1971, who borrowed the term “endosomatic instruments” (internal organs) from the 1945 work of American physical chemist Alfred Lotka, albeit applied or used as synonym for capital equipment (things people use around them to enjoy life). [2] In Georgescu-Roegen’s own words: [3]

“Exosomatic instruments enable man to obtain the same amount of low entropy with less expenditure of his own free energy than if he used only his endosomatic organs.”

Spanish ecologist Ramon Margalef defines exosomatic energy as: [4]

“[Exosomatic energy]: that which helps maintain life and the organization of ecosystems, but which neither flows though nor gets debased in the changes of somatic metabolism, and endosomatic energy, as energy that feeds the internal metabolism of organisms.”

Margalef adds, supposedly, that this term applies to all energy used in heating, transport, food preparation, air conditioning, the building and maintenance of dwellings, and information dissemination. [5] In these various contexts, it seems that the term exosomatic energy, as used in economics and ecology, is very ill-defined.

Human chemistry
In the modern formulation of human molecules reacting on surface, similar to the Haber process, it would seem that a good deal of what is referred to as an exosomatic instrument, e.g. a car or screw driver, is technically classified, from a chemical reaction point of view, as either substrate material or catalyst (e.g. iron in the Haber process), thus having an effect on the activation energy. In addition, in the sense of human chemical bonding, some of the energy aspects of this “exosomatic metabolism”, e.g. the energy of money being similar in properties to ATP as molecular currency, are classified as secondary field particles acting to mediate the force or exchange force between human molecules. [6]

References
1. Mayumi, Kozo. (2001). The Origins of Ecological Economics: the Bioeconomics of Georgescu-Roegen (pg. 116). Routledge.
2. Lotka, Alfred J. (1945). “The Law of Evolution as a Maximal Principle”, Human Biology, VIII, 188.
3. Georgescu-Roegen, Nicholas. (1971). The Entropy Law and the Economic Process (10.4: From the Struggle for Entropy to Social Conflict, pgs. 306-15; exosomatic, pgs. 19, 307-08). Cambridge, Massachusetts: Harvard University Press.
4. Margalef, Ramon. (1980). Biosphere between Thermodynamics and Game (La Biosfera Entre la Termodinamica y el Juego). Barcelona: Omega.
5. Fernández-Galiano, Luis and Carino, Gina (translator) (2000). Fire and Memory: On Architecture and Energy (exosomatic energy, pg. 5). MIT Press.
6. (a) Thims, Libb. (2007). Human Chemistry (Volume One) (Definition: substrate, pg. 33; Section: substrate and catalysts, pgs. 93-98; Keyword: substrate, pgs. 18, 32, 38, 40, 73, 92-93, 96-99, 101, 107, 129, 140-41, 186, 259, 280, 304) (preview), (Google books). Morrisville, NC: LuLu.
(b) Thims, Libb. (2007). Human Chemistry (Volume Two), (preview), (Google books). Morrisville, NC: LuLu.

Further reading
● Ramos-Martin, J. (2005): Complex Systems And Exosomatic Energy Metabolism Of Human Societies,
PhD, Autonomous university of Barcelona.