Final answer:
The gradual increase in exercise demands due to FITT principle modifications is known as progressive overload, which is essential for continual muscle strength and endurance improvements, involving systematic increases in exercise intensity.
Step-by-step explanation:
The gradual increase in exercise demands resulting from modifications to FITT principles is referred to as progressive overload. This concept is fundamental in designing effective exercise programs, particularly in strength training. By adhering to the FITT principles - Frequency, Intensity, Time, and Type of exercise - individuals can create a balanced workout routine. When applying the concept of progressive overload, one would systematically increase the demands on the musculoskeletal system to continually improve muscle strength and endurance. For example, if a person is weight lifting, to achieve increased muscle size and strength, the weight lifted must become progressively heavier. This increased load forces the muscles to adapt, and with time, even heavier weights must be used to challenge the muscles further and induce further growth and improvement. In summary, to promote long-term fitness gains and avoid plateaus, the intensity and difficulty level of exercises must evolve by manipulating aspects like heavier weights, more repetitions, or increased workout duration. This is in line with the understanding that muscles need to be constantly challenged to improve; without increasing the exercise intensity, muscle size and overall fitness levels may plateau.