Yes it could increase the strength,by a lot to be true.
I have once made an experimental exosuit on such a principle, so making one faster and stronger by overwriting their musclestrength using electricity. that thing worked, but only for specific movements since the emg sensors would not work due to the high voltage, so a old interface with pre programmed moves and simple methods of activating them was needed.
But be careful, while such a thing works, it will also damage the persons muscles exponentially, so it should only be used in extreme schenario's, just like adrenaline does, it can be done for very short amounts of time and up to a specific unknown and variable extend before the muscles damage to badly, or the person dies.
So how does this translate to the cybernetic spinal cord?
the cybernetic spinal cord might do one of the following things:
- it increases the voltage and current in ones muscles compared to what it would normally be.
- it can be hacked more easily to bypass what the body would normally force itself as a limit. this is very realistic since such a system likely would just listen to one specific section of the brain, most likely the conscious side, while the real limiting normally happens more in the subconscious side.
- it can make them more efficient or fast, if the brain is faster muscles can correct and control themselves faster, in reality this can severely increase ones actual strength and efficiency. and normal efficiency which can also be gained in other way like coordination and/or focus will also make one many times more efficient. if a normal person is capable of largely ignoring pain, has atleast a little strength, and has a high efficiency then they can do seemingly impossible things. most "strong" people now have a deficiency close to 0, look at people getting their strength from practical use or proper training like parcour, or people like bruce lee. the moves you mention would certainly be possible like that, when you look to things bruce lee could do without having that much muscle, just by having great control and being able to ignore pain somewhat, and what parcour people can do, than if you get in somewhere in between, so not even close to any of both's peaks then the moves from the movies are perfectly possible, you just have to find someone like bruce who like the freedom of movement, and/or the show a lot since it is just a showy way of attacking someone, not the most efficient but showy.
- it doesn't feel pain, or not all pain, or it doesn't send back the pain as well, perhaps it has a maximum amount of pain it can send back, so when the user reaches that it can bypass all the limiting as far as it wants. this would most likely happen due to things like adrenaline, but a trained person might be able to do so without. as a mater of fact there are people in real life who can bypass their bodies limits on bare willpower, often they use some form of excitement/will to replace adrenaline which allows them to go far beyond their bodies limit for quite long in many very small pulses. I know about someone who is does and did so in real life, the things that such people make happen would often sound ridiculous when you where not there to see it for yourself. yet often such people stay quite hidden because often they don't learn to train, and even when being better in something than others many prof teams do not want them, if they notice you are capable of doing it and are doing it, than many of them will not want you in their team, or even want to get rid of you, only if you get famous before they notice will they allow you to stay there. but in general it is seen as a great risk in multiple ways, since such a person often barely has technique so will often look wacky, or just bad in such a thing, they often lose feeling and expression of emotion which makes the sport look bad due to it seeming like someone beats the others by far without breaking a sweat. in fact that is actually true, and that leads to the last point of danger, many of them get physically cold when doing so, their body won't regulate itself properly and will behave it kind of like a body which is half dead, in some cases this can lead to things like the senses dropping(things like becoming temporarily blind, deaf, etc. such people however often don't really notice it themselves in those moments because they only care about what they want), so it is statistically seen very dangerous to the body. most people capable of doing such things are so from young on, almost no one learns it later in life, so most of their bodies can handle much more impact, they often use very short extreme impact forces to make the movements rather than long movements,however sometimes also longer movements with much force. but on a average person who's body is not used to it one such movement already has a large chance of seriously damaging the body. and even such a person can do so quite easily due to operating quite far beyond what the body should be able to do. often they also lose emotion and feeling partly when doing such things a lot which often might make them seem like monsters. but this is also their greatest weakness, many of them eventually seriously injure their body at multiple points, just like someone might do in extreme adrenaline schenario's, but such people don't do so during exercise, or while using their things, they instead often do so when doing nothing, or nothing serious like writing or typing. their body might eventually at random moments not be able to limit itself properly anymore, and so in some moments where it is supposed to be completely relaxed a very small muscle movement instead might be amplified so much that it can seriously injure them, things like ripping a muscle(partly) would normally only happen to people under severe load, to such people such a thing can happen when doing nothing and they might suddenly notice that muscle hurting a lot when trying to use it. such people however often just continue to do things, since they often just care about what they want, and some muscle pain often is not the end of them, soon they will again do such things, and when injured their might even rely on overwriting their body to do normal things.
Most people's strength and speed is limited by pain and relaxation of the mind(a average person get's up to around 1/5 the speed of what a decently fast persons brain speed can be, many people get a lot faster in the brain when in stress or adrenaline).
by removing the pain and relaxation you can become very strong because the removal of pain makes you strong, the increase of speed makes you much more efficient, and fast(impact force is amplified by speed, this impact force does not only apply to hitting things but also to starting a movement)
for the efficiency you can look to a bodybuilder and a old time farmer the body builder has huge muscles but won't really be strong due to a lack of control in them and a lack in speed in using them. a old time farmer might barely have muscle but they can be superhuman strong because they are so efficient with it(and they often have had to endure more pain, stressful (high speed(like falling, having something falling, animals, etc.)) situations which also makes them stronger and faster for the amount of muscle they have. some old time farmers can (almost)litteraly do such things like in the movies, a local oldtime farmer here was called the oak because he could turn his body into oak, that was just by tensening his muscles he could make himself so hard that even the strongest people where incapable of moving him, many such people also could stiffener their finger to be able to pierce right through hard things, later this became a famous movie stunt in karate things, but in reality around here some untrained farmers could do so due to the sheer efficiency they had in the control of their body, and due to the increased reaction speed and relative strength due to things like being exposed to painful situations more.
know that if we combine these things where it might overide the voltage and current, increase frequency of the brain(this automatically often gets triggered due to the higher voltage and/or traumatic or dangerous events like a fight accident/adrealine), higher efficiency and coordination, lower pain, or no pain, being able to override pain/or bypas the pain based muscle limiters, and the person daring to do things and learn/try moves. then by combining these things you could actually go far beyond the moves you described, and such things could be considered easy/very much possible. but they are just not the most efficient in a fight, so someone capable might be less likely to use it, unless they just think it is cool and want to do it. to be able to do such things to the full extend you have to think like a kid, or more feel actually since a kid often judges more in feeling than thinking(here feeling is just what feels cool, or what one wants or doesn't want) since such movies are more common now, someone who gets back to such a level is more likely to do it because it is in their mind. however due to society such a person is much less likely to be without any weird things like such a spine or specific events.