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 .
Some racing classes such as drag racing’s Nostalgia Top Fuel restrict the size of the fuel pump. To meet the class requirement, racers use oversize fuel pumps with inlet restrictions. That is providing extra fuel for more power benefits at lower engine speeds and a whole new era of tuning tricks. For example, in Nostalgia A-Fuel drag racing, class rules in the USA specify a fuel pump of approximately 12 GPM. The latest trick is to use a larger fuel pump that would flow approximately 15 GPM without any restrictor. An inlet restrictor limits the fuel pump output back to the 12 GPM value. Because this rating is made at a specific fuel pressure and fuel pump speed, the 12 GPM value is sustained at lower pump speeds. For nitro racing, that provides extra power at low engine-RPM from all of the oxygen in the nitro fuel mixture.
I have a question for you regarding with the effectiveness of the bathmate hydromax pumps .. you see its been like 2 months since I bought my x40 and I’ve been using it pretty much every single day ever since .. many of those days , 2 times in a 24 hour period .. aggressively and intensively. My size before I bought it was 6,5 inches length and middle girth and close to inches base girth, I did only ulis before that, from which I might have benefited 0,4 or 0,5 cm in girth maybe in a 1,5 year period .. I still do ulis after my bathmate sessions which kinda help with the donut effect … On a good day, after a good workout , my girth in the middle reaches an impressive 7 inches … The only problem ? Absolutely NO permanent gains up untill now … Why ? Should I quit ? It’s been like 2 months already of daily and consistant workout. What is your opinion Mark ..