Final answer:
The Principle of Progression dictates that exercise intensity should be increased gradually to safely and effectively improve fitness, while considering individual variability in exercise response due to genetic differences in muscle fibers.
Step-by-step explanation:
The principle of exercise that states a person should start slowly and increase gradually is known as the Principle of Progression. This principle advises that to improve your fitness, you should gradually increase the intensity and workload over time. It's an approach that helps the body adapt without causing excessive strain that can lead to injuries.
Individual responses to exercise may vary widely, with genetic factors playing a significant role. For instance, differences in the composition of slow-twitch and fast-twitch muscle fibers can affect how people respond to different types of exercise, thus affecting their training outcomes. Moreover, the principle of Overload is essential for effective strength training, intimating the necessity to continually increase the intensity for muscle growth and strength gains.