There's one very simple principle that will always unlock the door to physical improvement - progressive resistance. Progressive resistance is basically nothing more than a fancy way of saying that your body must always be confronted with something new or it won't improve. As an example, when you first began your weight training or cardiovascular program, you probably encountered good results for the first several weeks. Although your program may not have changed in those first several weeks, your body continued to see improvement. Then, you hit a brick wall. That same program was no longer effective. It's simple really; your body just got used to what you were doing to it and didn't need to adapt any further. Now, it's time to change your workout in order to change your body. That change can be anything from increasing the weight used per set, changing the number of repetitions or sets, adding a new exercise, altering your rest periods between sets, or any combination of the above, plus a whole host of other variables that can introduce a new training stimulus into your program.