Aclient's increase in biceps strength from performing dumbbell curls is evidence of which fitness principle?

The correct answer is specificity principle

Explanation:

General physical fitness is necessary for participating and playing any game but to improve a particular skill which is required in a particular game the principle of specificity comes into play.

For example, a weight lifter will do specific training to improve its muscle strength like lifting heavy weights while a cross country runner will focus on endurance training than improving muscle strength and power.  

So increasing biceps strength by performing dumbbell curls is the example and evidence of specificity principle.