We all respond differently to different training stimulus. Therefor programming needs to adapted to an athlete's personal capabilities, strengths & weaknesses.

The term specificity simply implies that training needs to be targeted towards what your aiming to improve. This can refer to a certain sport, capacitie or movement.

Probably the most important training principle. Progressive overload is the key for continuous improvement over time. The principle implies gradually increasing load in order to stimulate muscular growth.

Variation in training is a key factor for keeping training interesting and exciting in the long run. Additionally, there need to be a certain variation in the excersices, sets, reps and periodisation in order to avoid stagnation and allow improvement.