Are the bundles found in your muscles.
sets
myofibrils
fibers
fascicles

It is fibers. The bundles of fibers are surrounded by a tissue inside the cell.
Hope I helped

People who utilizes the progression principle will ensure their exercise program increases in frequency, intensity, time, and type. the changes need to happen gradually in order to ensure they make gains in their fitness program. a person who doesn't utilize the progression principle can still gain health benefits from exercising, but will not continue to improve in cardiovascular fitness.

What do you mean exactly