What could someone who is able to add to their muscle mass accomplish?

Question

In my world I have a type of magic user who grows stronger the more they kill animals and people.

Currently I conceptualise this as a sort of pocket dimension muscle, whenever they kill a creature, its muscle mass gets added to that pocket dimension. When the user wants to augment their strength, they can exert this 'magic muscle' instead.

For example, if they killed a 80kg man with 40% muscle mass, the magic user would gain about 32kgs (80 x 0.4) of muscle to use. This magic muscle matches whatever parts of the users body are being exerted. So when they throw a punch, that 32kgs of muscle is being divided up and added to their arms, shoulders, hips, legs.

The actual composition of the users body isn't changing, they're not growing larger/heavier, so leverage and bone density are still limitations on their abilities. The magic is acting like an exoskeleton, being exerted instead of their body, but matching its movements.

Additional information that might be important for people much smarter than me:

• The story is set in an alt history south pacific (the Cook Islands, to be pacific specific), so in terms of animals they can gain strength from, they're limited to fish, dogs, pigs, birds, and the occasional whale.

• The composition of this magic muscle is dependent on the animals its being taken from, so gaining extra fast twitch fibers for extra speed is possible, even if the original animals anatomy isn't analogous to a human (the muscles in a crayfish's tail could be used to augment the magic users arms, etc).

• I'm aware of, and willing to handwave a small violation to the laws of physics regarding the 'gaining' of strength. Since the dead animals body mass isn't going anywhere or shrinking, the magic user is technically adding energy into the universe by copying the animal's body mass. For the pedants out there, let's say there's a distant star that is getting 0.00000000000001% dimmer to compensate for this.

How much stronger would these people be compared to the average person? What kind of feats could they pull off?

Additionally, are there certain animals they'd value killing over others, for reasons other than pure muscle mass? (Unique composition, high fast-twitch fiber ratio)

Answer 1

This method gives you a two fold benefit,

• When you so choose, you operate at the peak human condition. Not superhuman (as that would shatter your bones, ligaments, muscles ...) but peak human. This is very important for adventurers, soldiers, crime fighters, fire fighters, messengers ..., basically anybody who needs to be able to physically perform at high level intermittently.
• (The more advantageous one) You can maintain this peak condition for the long periods of time regardless your actual physical state.

If you can channel this virtual muscle mass, you are also able to avoid the drawbacks of exhaustion, by gradually exhausting the virtual muscles at no expense to your physical body. I.e. your sugar levels, lactic acid level, and other markers of exhaustion do not change the way they would had you used your actual muscles.

Two model situation: Imagine a fire fighter who is charged with, for example of 48 hours worth of peak human condition virtual muscles. It helps him in daily operations (when he needs to pry open a car door, carry out the victims, run in and out of burning buildings (Even in full sprint his oxygen depletion stays at rest state, as the virtual muscles are those burning the extra oxygen) or perhaps even handling a hose with water pressure, he would otherwise be unable to handle. This boon is especially noticeable in case of prolonged activity. Imagine a natural disaster, such as flooding, with people trapped under the rubble, inside buildings and various currents, now imagine a unit of emergency responders who can operate at full speed, full strain for 24 or even more hours (essentially until brain needs a rest). Every mundane physical activity that needs to be performed can be performed by these people for tens of hours. Have you ever shoveled rubble? You get tired in under an hour. These guys, 13 hours later, they are still going fresh.

This would be a godsend for everyone who relies in his physical condition.

To put it into perspective per this article: https://journals.physiology.org/doi/full/10.1152/japplphysiol.00947.2009 a human body can theoretically endure a run speed of 69 kmph (Usain Bolt in his world record 100m sprint maxed out around 45 kmph). Imagine you can maintain this speed for 21 hours. In under a day, a charged messenger could run from Paris to Rome a distance of 1436 km (per google maps) less then 7 hours longer then via a car.

EDIT: Wrote the first version on mobile, so I expanded a little and cleaned it up.