Powerlifting and bodybuilding.
Want to gain muscle definition? You’ll be pumping your body to failure on most reps, or “faking failure” with HRT training.
Periodization will be your friend too. Splitting workouts into the generic “chest day/ leg day/ back day/ shoulder day” doesnt work in fitness, but if you want definition thats the best way to go. It allows you to really push one area while giving the other areas adequate time to recover.
Muscle definition is about the muscle ‘showing;’ I agree with the other posters in that this translates to a proper diet (one with the proper amount of dietary fat) and through exercise (using the muscles helps them grow and shine through). The amount of definition is definitely related to one’s genetic makeup and other factors such as hormones, so as I always remind my clients, “don’t compare yourself to others, compare yourself to yourself.”
Genetics does play a role however, what you do with it is another issue. Proper nutrition and balance of Protein, Carbs, Fat and Hydraytion. Strength training will also be important as well as aerobic activity. If you are prepairing for a fitness or bodybuilding contest, your nutrition will change drastically, RDA usually will not apply. I have a few before/after photos of past clients posted in my “Success Stories”.