Fred Hatfield, PhD, is better known as Dr. Squat.
He's written a number of excellent articles. The one I want to call to your attention is this one about training systems:
Popular Training Systems: Are They Really "Systems?"
This isn't a new article, but it's a very good one.
The real meat of the article for me is the part titled "THE SCIENTIFIC PRINCIPLES BEHIND WEIGHT TRAINING."
Dr. Squat gives an excellent, short, and readable rundown on the basic scientific principles that form the basis of weight training.
The Principle Of Individual Differences - We all react the same in a general way, but each person's specific response is different. What happens you body and mine when we lift a maximal weight is generally the same, but our results will almost certainly vary. We are all the same in general but to quote Monty Python, "We are all individuals!"
The Overcompensation Principle - Your body will react to stress by getting ready not only to match it next time, but beat it. Lift a maximal weight once and your body will try to get strong enough to lift a (slightly) heavier weight next time.
The Overload Principle - You must give your body more stress than its used to in order to get it to supercompensate.
The SAID Principle - Specific Adaptation to Imposed Demands, or, your body adapts to what you do - if you demand endurance, it'll react with endurance improvements, not strength, for example.
The Use/Disuse Principle - basically, use it or lose it.
The Specificity Principle - you get more efficient at a specific movement or activity by doing it more often. This is part of the explanation behind the "Grease the groove" method and the phrase "practice makes permanent."
The GAS Principle - the General Adaptation Syndrome, which describes how your body reacts to overload, then resists overload, and is then exhausted, setting the stage for recovery and overcompensation (if you're smart and rest) or dysfunction (if you don't).
Understanding those principles provides you with the tools to evaluate your own exercise program and those of others. Dr. Squat's article explains them in more detail than my summary, and explains them well.