What principle of exercise states that the only way to improve fitness is to increase one variable, such as resistance or repetitions, as your fitness level improves?

Overload: A principle of exercise that states that the only way to improve fitness is to increase over time. This can mean increasing the amount of resistance, increasing the amount of time, or increasing the speed. When just beginning an exercise, it is generally difficult

it would be a lot of diff ones. hope this ! < 3 : )

true. these things define the personality of the person.