Final answer:
The sentence should replace the word in italics with "Principles" to enhance its precision in discussing physical health improvement through specificity and progression.
Explanation:
Principles is the word that should be replaced with italics to make the sentence more precise. In the context of improving physical health, specificity and progression are fundamental principles that shape effective workouts and fitness routines. Specificity focuses on targeting specific body systems, while progression involves gradually increasing the intensity of exercises.
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