> 1. Training Theory: Basic Concepts

The main focus behind any systematic exercise is progression. A properly structured routine will result in an athlete improving in their discipline over time. This is accomplished through the biological law of adaptation - the adjustment of an organism to the stresses in its environment.

In sport, the athlete adapts to the stresses they're placed under. 4 aspects of adaptation that are especially important for training are:

1. Overload
2. Accommodation
3. Specificity
4. Individualization

< Overload (Magnitude of Stimulus)
Bringing about positive adaptations in an athlete requires a stimulus that is above habitual levels. There are two ways to increase the magnitude of stimulus: increasing the training load (increasing volume or intensity), or changing the exercise (given less accommodation). 

< Accommodation
As athletes are repeatedly exposed to the same stimulus, their adaptation response decreases with each successive exposure. This is considered a general law of biology, where the response of a biological object to a constant stimulus decreases over time. This makes the principle of diminishing returns a consideration in sports training for when athletes are adapted enough to a stimulus that increased levels bring little appreciable adaptation.

< Specificity
Training adaptations are highly specific. Strength training increases muscle mass and strength. Endurance training induces increases in aerobic capacity and increased blood volume. For sport training to be successful, exercise that mirrors the general conditions of the specific sport should be used. 

< Individualization
Everyone reacts to stimulus in their own way. Basically be flexible with it, find your groove and what fits you.

These factors are the most basic building blocks of exercise planning, and answer the most rudimentary questions in building a routine (what kind of exercises should I do, how much should I do, and what will this achieve?). Remember, progression is the hallmark of a successful exercise routine. Always think of how you will progress.