Final answer:
b Principles.
To make the sentence more precise, replace 'things' with 'principles.' Specificity and progression are fundamentals of sound fitness training aimed at improving personal physical health goals through tailored exercises.
Step-by-step explanation:
The word in italics, "things," should be replaced with principles to make the sentence more precise. Specificity and progression are two key principles of an effective fitness program. These principles guide the development of a workout regimen that is tailored to an individual’s fitness goals and abilities, ensuring continual improvement and adaptation of the body. For example, as one's muscular endurance improves through aerobic exercises like cycling or running, the principle of progression dictates that the intensity or duration of exercise should gradually increase to maintain advancement in physical health. Similarly, specificity entails choosing exercises that are directly related to one's goals.
Studies indicate that exercise and healthy lifestyle choices can slow down the deterioration of the body that comes with old age. Therefore, by adhering to the principles of specificity and progression, individuals can not only enhance their physical health, but also potentially extend their life span and improve their agility, akin to the benefits seen with activities like ballroom dancing.