Final answer:
To incorporate progressive overload, the PT should increase resistance gradually, which requires a slight increase in resistance over time to continually challenge and grow muscles.
Step-by-step explanation:
The principle of progressive overload is a key concept in resistance training and physical fitness. To incorporate the principle of progressive overload, the Personal Trainer (PT) should increase resistance gradually. This means making a slight increase in resistance over time to continually challenge the muscles. For effective strength training, it is essential to increase the intensity of the exercise. Increasing the frequency or altering the target can also contribute to progressive overload, but the question specifically refers to resistance, which aligns directly with the need to increase lifting weights to stimulate muscle growth and adaptation. Through this method, muscles become capable of handling heavier loads over time, and this progression is what leads to improved fitness and muscle mass.