Dagon's Saiyan Physiology & Ki Theory[/div]
Do Saiyans have naturally superhuman physiology, or does their superhuman strength come from their ki?
Saiyans have human-level physiological strength and durability. Saiyans' superior strength comes from their superior ability to improve their ki.
Counter-Point 1: Goku, as a child, survived a bullet to the head from a handgun. This would prove Goku has superhuman durability. Goku threw a large log several-dozen feet into the air and proceeded to punch it into several pieces. These two events happened before Goku was trained by Roshi, which includes Roshi's ki training, which would mean Goku doesn't have knowledge of ki. Thus, this proves Goku has superhuman strength and durability even as a child.
Rebuttal: Goku fired a Kamehameha just by seeing it done once, before any of Roshi's training. Goku also said Grandpa Gohan taught him some martial arts before his death. Thus, Goku has knowledge of ki prior to Roshi's training.
Furthermore, Saiyan infants and children have the ability to use ki before any formal training. Saiyan children were used to wipe out whole civilizations with no formal training. In Dragon Ball Super, Pan is able to fly and use her ki as an infant. Thus, Saiyan infants and children have an innate talent for using ki.
Lastly, a suppressed adult Goku was scratched by the bullet of a similar handgun to Bulma's. Thus, Adult Goku's pysiological durability, combined with some limited amount of ki, is within the realm of less than bullet level.
Counter-Point 2: Saiyan children are "programmed" before being sent to planets, which can include knowledge of ki use. Goku would have lost this knowledge when he hit his head and forgot everything. Pan could have had the Ultimate powerup transfered to her from her father, Gohan. Goku could have been shot with a more powerful handgun/bullet than the one Bulma fired.
Rebuttal 2: There is no statement regarding the thug's handgun that shot adult Goku in DBS. Thus we cannot conclude that it must be more powerful than an average handgun. To purport such is an assumption.
Regardless of Pan's power inheritance, Saiyan babies can withstand the 10x gravity of Planet Vegeta even when in the womb and post-birth, which would be prior to any knowledge that could be planted in their brains.
Combine suppressed Adult Goku being less-than-bullet level, with Saiyan babies withstanding 10G in-utero, Goku having knowledge/talent for ki prior to formal training, and the conclusion left is that Saiyans have human-level physiology with a natural talent for using ki and improving their ki.
Toriyama's thoughts on physical limits and ki:
https://www.kanzenshuu.com/translations/daizenshuu-6-akira-toriyama-super-interview/
Daizenshuu 6 Akira Toriyama Super Interview
Incidentally, what led you to have Goku become a Super Saiyan, or the villains to level up?
I was feeling that there were limits on mere strength, so I was generally always struggling to come up with something. I actually hadn’t planned Goku’s Super Saiyan transformation at all. Then, when I came up with the idea of the Super Saiyan, in order to show that Goku had gained a massive power-up all at once, I thought “there’s no choice but to change his form, too”. But in terms of design, the facial expressions and such would become like the design for a villain. I felt, “I wonder if it’s really OK for him to be like this.” Granted, since his transformation is accompanied by rage, I also thought, “I suppose that part’s fine.” It was a pretty radical concept. With respect to the villains, my editor would say, for instance, “I don’t like this”, and in those circumstances, I’d change it. (laughs) Before long, “they should transform” became the norm, so that was a pain.
https://www.kanzenshuu.com/translations/seg-story-volume-truth-about-dragon-ball/
SEG Story Volume The Truth About Dragon Ball
What is the key to winning in battle?
In battle, the most important thing is the size of your ki, and your control over it. Ki as a concept of course includes such spiritual powers as energy [genki], courage [yūki], and right-mindedness [shōki]11. No matter how much you train, there are limits to physical strength, and the only way to overcome that is through ki. I think Goku was able to approach the mightiest warriors in the universe through strengthening his ki.
"Mere strength" = "physical strength", synonymous with physiological strength. Toriyama says there is a limit to physical/physiological strength. Ki is the only way to overcome this limit. Ki is also the most important thing in battle. Furthermore, Toriyama says strengthening his ki was the reason Goku was able to become one of the mightiest warriors in the universe. This indicates ki is the determining factor for Saiyans' superhuman feats.
Questions:
"If ki is the reason Goku is superhuman, how does his training work? If Goku uses his ki during training, wouldn't that make his body soft from his ki making the training easier?"
No, not if Goku is exerting himself
both physically and with his ki at 100%. If both his physical and ki efforts are at their fullest, he will both improve his maximum ki level, and transitively exercise his physical body, thus keeping it in top shape.
"Wouldn't it be better not to use ki so that Goku could improve his physical state further and further?"
That would only be true if Goku's physical state were less than the utmost peak of physical fitness. If Goku still had room to improve his body, then training his body to perfection first and foremost would be the best course of action. But as we know, Goku is in great physical shape, so training without ki is unnecessary, as his physical state will still be maintained even when he trains with ki, as long as the training is hard enough to make Goku exert himself to the fullest.
The Theory in Practice:
How does this all work? How does Goku's physical state relate to his ki levels?
Imagine it like this:
Peak Physical Goku with 100% effort combined with 100% ki = 100% force exerted.
Weak Physical Goku with 100% effort combined with 100% ki = less than 100% force exerted.
Goku's physical state translates into the force exerted by his ki. Let's use Buu arc Goku as an example. While flying, base Goku failed to lift 40 tons, 10 tons strapped to each limb. Let's say, Goku at his peak physical state, while using 100% of his base ki, would successfully bench press 20 tons(his arm weights combined) once. His one-rep max. For this example, this weight
abolutely requires 100% of Base Goku's ki. If Goku does not use 100% of his ki, he will fail to lift.
Now make Goku's physical body half as strong. Feed him doughnuts and make him lounge on a couch until he's half as physically fit as he used to be. For argument's sake we're going to say he is PRECISELY half as physically strong. Despite this, we're going to give him the same power level as fit Goku. If you read his ki, it's going to read as the same level as before, for peak fit Goku. Now, physically weak Goku, even with 100% of his ki, is going to max out at less than his previous one-rep max. For this example we'll say Goku's physical state translates directly into the force exerted by his ki. So a Goku that is precisely half as physically fitas prior is going to lift precisely half as much as fit Goku, even with 100% ki: 10 tons. For this example, unfit Goku exerts half as much force as fit Goku, even with the same power level.
This would be the same as if fit Goku powered down to 50% of his ki, and use 100% of his effort to lift 10 tons. It would also be the same as if fit Goku used 100% of his ki but 50% of his effort to lift 10 tons.
"If Goku needs ki to lift that weight, and his body is at a peak level, wouldn't that mean he won't get stronger at all? Physical state determines ki level, right?"
No, even if his body is in peak condition, he can still improve his overall level by pushing the limits of his ki with his training. Physical state is not reflective of ki level, as we've seen people of various fitness levels with various power levels in the series. If Goku trains with 40 tons for long enough, his upper ki limit will increase, while his body remains at its peak state because it can't improve anymore.
"How exactly does this effect Goku's physical body?"
It effects it the same as if he used no ki at all and trained at a human level. His body receives hypertrophy, micro-tears in the muscle, fat burning, etc. But if Goku used no ki at all and only trained his physical state, it wouldn't benefit his overall level because his body is already as strong as it can get. Ordinarily, over-exerting your muscles causes them to grow stronger once they regenerate, and similarly, over-exerting your cardiovascular system improves your stamina once your body recovers. Progressive overload is the key principle to physical fitness improvement. Progressively go beyond your physical limits to make your body stronger steadily over time.
But what if your body is already as strong as it can get? That's where ki comes in. In a very similar way to physical progressive overload, Dragon Ball charcters progresively oveload their ki exertion and acquire a greater ki level upon recovery. Goku won't be able to improve his ki level without this progressive overload, and since ki is exerted through effort, when Goku progressively overloads his ki exertion, he is directly and transitively doing the same for his body. The difference is that his ki can continue to improve, while his body will merely recover back to its previous peak state.
"If Goku's body can't improve beyond human levels, shouldn't that mean it would fail to contain exceptionally large levels of ki?"
Saiyan character's ability to handle ki is determined by their power level and skill level with ki control. Goku at a power level of 8,000 suffered damage under Kaio-Ken x3 and x4. Yet, later, a power level of 90,000 can handle the force of Kaio-Ken x10, and 3 million can handle KKx20.
Counter-Point: That could just as easily be Goku's physical body getting stronger in order ot handle the ki increase that Kaio-Ken causes at those levels.
Rebuttal: The Daizenshuu 7 Special Attack Dictionary specifies power level as the factor that determines the multiplier limit of Kaio-Ken:
http://web.archive.org/web/20111103182002/http://kanzentai.com/trans-daiz07.php?m=04&id=attack_j-l#link
Daizenshuu 7 Special Attack Dictionary said:
Kaio-ken
[kaiou-ken; lit. "Fist of the King of Worlds"]
First Appears
Chapter 226
Category
Ki Manipulation
User(s)
Son Goku
Characteristics
A technique that instantly amplifies the ki inside one's body, multiplying all one's abilities, including power, speed, defense, etc. Since it makes one capable of utilizing battle power many times their own ability, it is extraordinarily effective during battles with formidable opponents. However, because it is impossible to multiply excessively far beyond one's abilities, experimenting with an unreasonably high Kaio-ken might destroy one's own body. When the user's battle power is 8,000, their limit is x2, and when they are at 3 million the limit is x10. However, since real battles are harsh, Goku often had to use Kaio-ken above those limits. The Kaio-ken's designer is the North Kaio, but Goku was the first person to be able to master it. (Daizenshuu 2, p.212 / Daizenshuu 4, p.113)
The "limit of one's own ability" here is referring to power level, i.e. ki level, as evidenced by the proceeding sentences.
Thus, what determines how well someone handles an amount of ki is their personal skill and control over ki, and the ki they already have. Think about it like this:
How do you use water to hold a body of water? Make a bowl of ice. If the ice starts to fail from additional water weight? Add more ice. Thus water can be used to hold more water. Or rather, water can be used to hold the WEIGHT of more water. Because it's not the QUANTITY of water that would fracture the ice, it's the weight of the water; The force of the water that is exerted onto the ice via gravity.
Thus, the force that ki imparts unto the body can be controlled with the a quantity of ki and skill with ki.
"If that is true, wouldn't that mean that their power level would effectively be lower since a portion of it is being used to control the other portion?"
No. If you have a 100KG bowl of ice holding 50kg of liquid water, how many kilograms of water do you have? It's not 50kg, it's 150kg, because Ice is still water, and it still contributes to the total weight of the combined mass. 150kg's worth of force > 100kg or 50kg of force.
This would mean for something like Super Saiyan Grade 2 or Grade 3, Future Trunks could use a portion of his ki to control the other portion of his ki, and still punch with the force of all of his ki.
IN SUMMATION
Saiyan physiology is the same level as human physiology. The superhuman feats of Saiyans is due to their use of ki and natural talent for increasing their ki level.
There are some posts from others that I will address in time but I wanted to post this today.
The world champ took on Cell, Boo and Beerus and he didn't need no cheap Ki tricks to win. 
