What would be the best way to permanently increase a human's speed, strength, stamina, and durability? I'm looking to create a world in which the majority of humans realize how weak and feeble their bodies actually are and they have found a way to change this. However, I need help on the actual "way". I'm not scientific at all but I don't want to be cliche by giving them a serum or a pill. I was looking for something that would require surgery. The use of some sort of technology would be ideal but it is not absolutely necessary.
At least for stamina, you could read up about "the man who can run forever": Dean Karnazes (https://www.theguardian.com/lifeandstyle/the-running-blog/2013/aug/30/dean-karnazes-man-run-forever).
Karnazes' ability to run for inhuman distances seems par for the course with other endurance athletes, but what sets him apart is that he honestly does not show signs of muscle fatigue AT ALL. The article explains it all, but if you want a quick summary, here it is:
Basically, your muscles send out fatigue signals when lactic acid builds up from anaerobic exertion - this is when you begin to feel tired. For Karnazes, his body clears lactic acid so efficiently that his muscles never send such signals, and thus he never feels tired. As such, he can basically keep up a decent running pace for as long as he can stay awake.
How does this relate to your question? Imagine that you were able to create some nanobot with the ability to metabolize lactic acid. Inject this nanobot into your subject, and voila! He now has superhuman stamina.
The thing to remember is that every attribute comes with a cost. Cheetahs are fast — but they have almost no fat reserves, and not much of anything else. Race horses have been bred to be really fast — but are always on the edge of breaking legs by overdoing what they do best. For humans — muscles consume a significant amount of our food resources, even at rest. That's why they atrophy very quickly if not used. Our big brains are supposed to be useful (they've allowed us to conquer the whole planet) but use about a third of the calories we consume. Plus, too strong, you could break bones or dislocate joints.
There's a very good short story by Larry Niven called "Brenda". It discusses the problems with breeding super warriors — double gene for night vision causes daytime blindness, doubled gene for blood clot (stop wounds bleeding) leads to blood clots and stroked by age 40 or 50. And so on.
The fastest are rarely the strongest; pick one or the other (look at the Olympics). Plus, human scale is designed for the size we are. Bigger, taller, or carrying a bigger load means thicker bones meaning slower running. Unless you're looking for some magical formula where the muscles operate say, 20% more efficiently.
The same one that works now, exercise and training. If you want to make your new human more fit, just make them enjoy exercise more than normal humans. Minimal changes to the human, just a few changes to the initial wiring of the brain, and it can be spread organically(breeding) or artificially (genetic manipulation). If going to gym was as pleasurable as going to the strip joint, bar, or dunkin donuts you would have a stronger, faster and more fit populace.
I imagine that you could use implanted stem cells to increase muscle mass, as these cells will usually change into whatever kind of tissue surrounds them. This solution would improve speed and strength.
By combining stem cells with genetic modification you could theoretically create entirely new organs to implant in a human. This isn't even too far fetched based on modern science. The genome editing molecule known as CRISPR-Cas9 is relatively new, but allows scientists to splice DNA from different organisms together with much more specificity than was ever previously possible. With this technology you could give people bird hearts and lungs (which are much more efficient than mammals') or something even more amazing.
If you want more inspiration, I recommend looking through this link detailing the process to create a Space Marine in the Warhammer 40,000 Universe.
They have extra hearts and lungs for added stamina, and they take dietary supplements which add different minerals to their bones for more durability.
Get Rid of Chemical Energy
Muscles are simply polymers. An electrical signal tells them to wind themselves up (contract) or unwind (relax). They're not very good ones either, but they've got an amazing amount of control, ultimately using a chemical as an energy source ATP -> ADP, and generating a waste product (lactic acid) for this energy conversion. Overall it's messy and irreversible, which causes the non-linear strength, speed, and stamina problems. The reaction rates simply can't happen fast enough for all three to be increased simultaneously.
Using Electrical Energy
By converting to Electroactive Polymers, a type of artificial muscle, the waste product is simply the drop in voltage. Stamina is unlimited - so long as you have an electric source, you're muscles keep working. Does your laptop complain "it's tired"? No! It complains it's battery is out. So long as you have futuristic energy storage, this isn't going to be a problem.
To add strength, increase the voltage. To add speed, increase the current. If you have limited energy storage, increasing one of these will necessitate decreasing another. But with unlimited energy, then all three could be enhanced well beyond human limits.
Cyborgs then, requires technology and surgery.
Your weak arm muscles? replaced with basically a nanoweave of hydralics
Bones? Bah we use titanium
They can be powered both by electricity/converting fat/stealing energy from the digestive tract.
Another route would be to simply have worked out a more efficient cell structure/ biological processes, a more efficient way of binding oxygen could improve the supply of oxygen to the cells etc. There are many inefficiencies in the human body that could be improved upon.
You could make them really big, like giants, and hope that it would scale these stats up - they'd be faster because their legs would be longer, more durable because things wouldn't hurt them as much because "oh it's just a little scratch", and they probably wouldn't need as much stamina - but they'd need to eat a lot more to sustain their huge size.
A very permanent way would be altering the human genetic code. Not only would this alteration enhance the human you first use it on, the change is going to remain evident throughout the rest of their descendants as well. We already use genetic therapy on foodstuffs to increase their quantity and quality.
Genetic therapy already exists for humans and involves inserting genes to fix problems instead of drugs or surgery. For some genetic conditions this is the only course of action that will succeed. In the case of humans you would find desirable traits and locate the code that works with these traits. For example, once all code related to metabolism is understood, you could change the genetic code to ensure a person gets the most out of every meal they have with little waste.
The most realistic method would be to simply remove any and all defects that will possibly transfer via genetics or bloodline. History of heart disease? Wiped out. Genetic disposition for astigmatism? Wiped out. You'll be able to undo or prevent an assortment of problems from ever occurring.
This does open up the potential to have an ugly backlash though, an unforeseen issue that might arise with the tampering could be difficult to fix, and it's not something that will just go away either.
A better way to look at it would be the ability to have the maximum human potential. You'll still have to act on it. The greatest genetic sequence in the world won't make a musclebound monster of a man if you never exercise or pick up weights.
(I've never given an answer before so sorry if this does something wrong)