To apply this principle, you should strive to use either more weight or do more reps for a given exercise. For example, let’s say you’re doing standing bicep curls. If your previous best curling weight was 100 pounds for 10 reps, then curling the same weight 11 times would qualify as progressive overload. Overloading the muscle ensures that it will continue to adapt by getting bigger and stronger. On the other hand, failing to overload the muscle gives your body no reason to grow bigger and stronger. Remember, muscle growth is an adaptation to stress imposed on the muscle during the workout. If your muscle is already equipped to handle a given weight for a certain number of reps, why would it need to adapt if you continue to perform the same workout time after time?
Another way to stimulate a muscle is to change the exercises you perform. As you can imagine, doing squats, leg presses and leg extensions for your quadriceps delivers a very different stimulus than hack squats, lunges or sissy squats. Neither routine is necessarily better than the other; each imparts a unique stimulus to the quads and other leg muscles. Alternating these two quad workouts can help you avoid stagnation that would likely occur if you were to continually repeat workouts. You should at least change two exercises every time you train, especially if you are a bodybuilder. For instance, if you train back and do 5-6 different exercises in a session, you may want to vary 2-3 of those from workout to workout.
You can also vary your routine by simply changing the order of your exercises. This allows you to focus on a given exercise earlier in your workout while you’re still fresh. Because you’re stronger at the start of your workout, you’re able to utilize heavier weight and/or do more reps than if you did the same exercise at the end of your routine. That allows you to recruit more muscle fibers. If you need to bring up your upper chest, for instance, doing incline barbell presses first allows you to use maximum poundage and reps on that exercise. Your upper chest muscles would be taxed by the time you started your other pec exercises, many of which would also hit the upper pecs to some degree. If you do inclines after flat-bench presses, there’s no way you can hit your upper chest with the same level of intensity, and it will continue to lag. Always starting a bodypart workout with the same exercise is a sure way to plateau in your progress. Back to the chest example, if you frequently do flat-bench presses first, consider starting your routine with an incline movement such as incline presses(barbell or dumbbell) or flyes in your next workout. The next time you hit your pecs, do a complete 180 and perform a lower-pec-dominant routine by beginning with decline presses. From a mental perspective, changing your routine prevents stagnation and boredom. If you become bored or feel no challenge or excitement from something new, you won’t put forth the effort necessary to stress the muscle enough to grow.