There are lots of programs, linear programs, periodic programs, bro-science programs, bodybuilder programs, etc. You name it, its out there waiting to be discovered. The good programs are designed around the two main limiting factors to physiology. The bad programs have no clue how the body works. The program you choose has to fit your goals, whether it is strength, endurance, or fat loss.
The first fundamental factor of creating a programming routine is fatigue. Fatigue is what causes your first plateau on a linear program. You keep adding weight to the bar each session for each workout. And you can complete your sets for many months doing this. You’ll have a few failures, but the next time you’ll come in and get that weight. Until it happens. You come in day after day. And you cannot hit the weight. Even though it is only five or ten pounds heavier than your last success, you can’t do it. Your muscles and central nervous system have been overloaded. Even if you don’t feel “sore” it doesn’t mean your body has recovered.
The second factor that needs to be taken into consideration is de-training. This is a simple concept: if you don’t use it, you lose it. Though, if you’ve been training it happens faster than you think.
Linear programs ignore fatigue, which is why they are generally used for beginners. You can physically stress your body and makes gains for a long while before the fatigue piles up enough to affect you. After six months or so most people permanently plateau with linear programs as a result of the fatigue. Periodic programs take into account fatigue, and work to prevent detraining while you recover. These programs allow you to recover from fatigue by working below max thresholds, which don’t add to your fatigue levels as much. And these lower work weights prevent detraining with their lower levels of physical stress.
The above graphic is a good representation of what happens after a workout. The physical stress causes short-term exhaustion. The period of recovery is what actually makes your gains real. If you don’t rest, eat, and recover you won’t get stronger. But if you don’t take advantage of the muscle building after recovery, you will lose those gains eventually as your body retreats to an equilibrium.