In human body, new cells are created every day which is not case with elastic band. Best anology could be economy. If you keep creating wealth and not spending one day you reach your limitations. Continously churning and creating gives boost to economy.
Some tissues generate new cells every day, but tons of relevant things to exercise such as cardiac muscle cells and the fibrocytes making up things like ligaments and tendons really don't. This also goes for most of the other stuff on the inside of your body.
