Re: What is the energetic breakdown for the human body?

I wasn't totally sure what you meant by total potential energy. 
Did you ask for the energy stored in all the chemical bonds in the human 
body? (I couldn't find an answer for that). 
I found some information on energy reserves in the human body though.
Energy reserves are 4 kJ of ATP, 15 kJ of creatine phosphate, 4600 kJ of 
glycogen and appr. 300000 kJ of fat (available for mechanical and other 
work without any danger of physical harm).
The power for minimal life processes is more or less described by 
the basal metabolic rate (at rest) which is appr. 1.2 W per kg of body 
weight, i.e. a human of 75 kg has a basic energy requirement of appr. 7800 
kJ per day to keep all the physiological processes (ion transport, 
digestion, respiration) going. This basal metabolic rate usually declines 
with age (the BMR is usually given in liters of oxygen consumed per kg of 
body weight per time which explains the more or less).

Approx. 20 per cent of the metabolic energy at rest is expended for brain 
activity which would be 1500 to 1600 kJ per day (or approx. 18.5 W). When 
you think hard this figure will go up slightly. Most of the extra energy 
required is because your muscle tone is raised as well (you're tensing up 
while thinking really hard!).
 
A really good athlete would expend about 21 kJ on a 100 m dash (at 36 km 
per hour) or 2.1 W. An untrained person would probably develop less power 
over the course of the run since his musculature and overall physiology are 
unable to perform at this level.

About 2 to 3 per cent of the total energy at rest are used for breathing.
That is about 150 to 200 kJ per day or 1.75 to 2.3 W. This would accord to 
approx. 5 to 6 J per inhalation (which lasts about 2 to 3 secs).
I found some other data stating that the mechanical power exerted by the 
respiratory musculature is 0.7 W and that the respiratory power is about 
0.7 to 1.4 W or 1 per cent of the total energy (oxygen) consumption.

I wasn't able to find any numbers on digestion (what would that include 
anyway? Only the energy for peristalsis or would that also include all the 
energy required to secrete enzymes, for resorption, etc.?) but managed to 
get some numbers for the circulatory system. 
The heart uses 1.2 J per heart beat (corresponding to 1.5 W).

I can't suggest any good American textbooks or books on this since I 
extracted most of the information from German textbooks but any major 
textbook of physiology and/or biophysics (which covers the topic in some 
depth) should provide the necessary information.

I hope this answers some of your questions.