A bit of background: One of my characters in a story has lost her right arm up to the shoulder, her left leg to the hip joint, right leg to just below the knee, the pinky and ring fingers of her left hand, and right eye to an explosion. THanks to cybernetics, these losses have been compensated for with cybernetic prosthetics. Each prosthetic weighs the exact same as the limb it is replacing, so she would not be expending extra energy to move them. What I'm wondering is; Since a little over a third of her body and almost all of her limbs are machine, would this woman's physical endurance be greater than a healthy, whole human of comparable physical condition, since there is less of her that her body has to power. The muscles related to getting from point A to B are machine, so in theory she does not need as much fuel to move. But would she be able to endure extreme physical activity for longer?
Where is the limbs's power coming from? I take it this is a sci-fy futuristic kind of prosthetics. Do they have some kind of sci-fy battery in them? Do they take energy from the host's body? If it's the second, then they still take energy like normal limbs, only the limbs themselves don't get exausted. As the author, it's up to you to decide if the prosthetic limbs spend more, less or the same amount of energy as the biological ones. If they work on batteries, then you have the advantage of spending less of the body's energy, which means being able to move for longer periods of time, with the caviat that every now and then you'll be swapping the batteries whenever the old ones are spent. That could make for some tense situations where the character can't move a leg or arm because the battery in that limb is dead.
The arm and legs draw energy from specialized batteries that are charged at night, while the fingers and eye are small enough that they can draw power from the electricity in the nervous system. I think that since the muscles most related to movement aren't drawing energy from her body anymore (Cuz they don't exist anymore), then her body's caloric needs would decrease, and therefore she would have more fuel at her disposal for the remaining part of her body. But I could be wrong
I wrote a story a while ago about a detective trying to hunt down someone with cybernetic prosthetics and I had to make up some rules for them. The power for them came from the body, using glucose extracted from the bloodstream to power small, enzymatic bioreactors within the prosthesis that was then stored via battery until the power was needed. This meant they wouldn't need to be plugged in, but given it's far less inefficient than straight up muscle, it also mean my suspect needed to consume more food than a normal human just to stay powered (noticeable in my society given it's high poverty rates and substantial class divide). It also meant that even though they were stronger and faster than normal humans, that they couldn't maintain it indefinitely and afterwards would need extra time to recharge their batteries. Also given that half their mass didn't have a metabolism, it meant that they didn't deal with cold very well. Their human bits would struggle to keep the cyborg bits warm which would cause core temperature to drop much faster, and all of the chemical reactions and carefully calculated viscosities of various fluids and lubricants within the prosthetics would change as temperatures dropped, causing the body parts to become less efficient and produce power more slowly.
That makes sense, but there's two different concepts to take into account. On one side, you have the general caloric reserves in the body, which get reduced by virtue of having less of a body. The caloric reserves will determine how long she can do physical activities. On the other side, you have the exhaution on each individual muscle. Muscles get exausted on the short term, but get back to good condition on their own while resting. All in all, I think she'll be be fine in the short run, but she'll struggle if the physical activity drags for too long.
IDK. On the one side, technically they would need less for building upkeep of missing muscle/bone/ skin/blood. And on the other side, if they work until physical exhaustion as if they were still whole, then maybe not. Though I would think that for the most part you can kinda guestimate based off the factors of a whole persons caloric needs, and figure out the difference in how much less they may need to consume to keep physically energized accounting for the subtraction of the muscle/bone/skin/blood that does not need to be accounted for. Age/Sex/Activity levels all play a factor as to how much caloric intake is required for a healthy person. https://health.gov/dietaryguidelines/2015/guidelines/appendix-2/#table-a2-1 https://health.gov/dietaryguidelines/2015/guidelines/appendix-2/ I know it isn't a specific answer, but it is a starting point with which to work with.
