Science is not a theory. It is a method. The difference, therefore, between science and pseudo-science is a difference of method, and not, at least not necessarily, a difference in the truth of theories. Thus, it is probably true that the body adapts to training so that training for running adapts the body to running, at least to some extent.
The article in Scientific American makes the same point:
The big difference Popper identifies between science and pseudo-science is a difference in attitude. While a pseudo-science is set up to look for evidence that supports its claims, Popper says, a science is set up to challenge its claims and look for evidence that might prove it false. In other words, pseudo-science seeks confirmations and science seeks falsifications.
In other words, pseudo-science seeks confirmations and science seeks falsifications.
Of course, not all scientists understand this point. Many scientists for example squirm whenever I say that Newton's Law of Universal Gravitation was falsified by the observation that Mercury wasn't quite at the place predicted by Newton's law, which led eventually to Einstein's General Relativity.
Indeed, many if not most scientists probably immediately stop doing science the day that they publish their results and start doing pseudo-science in that they stop trying to falsify their own theory, simply because it is human nature to cradle your baby and protect it against the barbarians.
Doing science is an attitude, to use the term of Scientific American, and people can change their attitude according to the circumstances.
Concerning the SAID principle, as with any such, the science is entirely in trying to falsify the theory, not at all in accepting or not the principle. It is perfectly acceptable to apply a principle if you think it is true. However, you cannot say this principle is science just because you think it is true. You can say you are doing science, ad this only when you are trying to falsify the principle.
Thus, contrary to what most scientists themselves probably believe, no scientific theory is science. A scientific theory is a theory. It is a claim. It is a claim waiting to be falsified. It doesn't mean anything to say that you have verified a theory when in fact all you can say is that you have failed to falsify it.
A scientific theory is merely the consensus of the moment the professionals who do science. However, the science was in falsifying the previously accepted theory, for example Newton, not in accepting the theory that replaces it.
It is not the scientific attitude to accept a theory simply because you have failed to falsify it. It is a rational attitude, but being rational doesn't make it science.
Science moves forward because of falsification. It is falsification that motivates people to work their arse off to find new innovative theories. Einstein was born out of Mercury's falsification of Newton. No Mercury, no Einstein. Human beings have proved they can believe the same crap for centuries.
That being said, sorry, I'm not going to tell you how you could falsify the SAID principle.