The efficiency of human muscle has been measured (in the context of rowing and cycling ) at 18% to 26%. The efficiency is defined as the ratio of mechanical work output to the total metabolic cost, as can be calculated from oxygen consumption. This low efficiency is the result of about 40% efficiency of generating ATP from food energy , losses in converting energy from ATP into mechanical work inside the muscle, and mechanical losses inside the body. The latter two losses are dependent on the type of exercise and the type of muscle fibers being used (fast-twitch or slow-twitch). For an overall efficiency of 20 percent, one watt of mechanical power is equivalent to kcal per hour. For example, one manufacturer of rowing equipment calibrates its rowing ergometer to count burned calories as equal to four times the actual mechanical work, plus 300 kcal per hour,  this amounts to about 20 percent efficiency at 250 watts of mechanical output. The mechanical energy output of a cyclic contraction can depend upon many factors, including activation timing, muscle strain trajectory, and rates of force rise & decay. These can be synthesized experimentally using work loop analysis .
But the fact is that the more that I look at this situation (swear to God or not), it is BS. No reference to physician testing. No mention of Lab results (the only way that you know what your TT or FT or SHBG or Prolactin or Estrogen levels are… which a physician would insist on knowing all of those). No mention of a physician doing initial testing to see what your LH and FSH levels were to see if you were primary hypogonadal or secondary hypogonadal (one of the causes for a young man past puberty start to be hypogonadal is a tumor on your pituitary gland… it is THAT serious – and isn’t caused by generic stress; long-term stress in the range of PTSD type stress could cause it in some cases).
I tried the cup of raisins before bed and woke up before dawn with an erection reminiscent of days gone by, that lasted for over an hour. Pretty awesome! Though peeing was a long and drawn out affair.
I just had my T checked as I was not getting them any more, neither was I much interested in sex. The test came back with a paltry 305 @ 46yrs old. Just a year ago my erections used to have a bitter sweet ache to them. After going close to zero carb I lost my power, my head hair, got rosacea, limp erections, and my nitric oxide plummeted. I stopped training as it was painful and although I was eager to exercise my body just didn’t seem up to it. ( come to think of it now after reading all these articles, it would seem that lower elasticity of my arteries(low NO) was the reason.)