First things first: it’s impossible to isolate any particular part of your body. Just because you’re performing a tricep pressdown, it doesn’t mean that only your tricep is working. Instead of thinking about muscles, it’s better to look at movements if you want to develop real strength, build muscle, and be resilient enough to live an active, pain free lifestyle.
Think about a pushup: your pecs, shoulders, and triceps are performing much of the work, but the muscles of your core and legs are all working isometrically to hold the position. If you balance out your program with pushing, pulling, and lower body exercises, you’ll challenge your body enough to force it to grow bigger and stronger, while also training it to be more efficient as a unit, which carries over to becoming a more athletic human.
This is a list of my personal favorite exercises for each movement pattern, and they make up the vast majority of my training programs. They all challenge your muscular system to a serious degree without beating up your joints. The beauty is, you can load them with a number of different tools to slightly change the stimulus, which is great for breaking up monotony and for avoiding overuse injuries.
Adjust the loading by utilizing barbells, dumbbells, medicine balls, sandbags, kettlebells, Fat Gripz, gymnastics rings, and add in isometric holds, longer eccentrics, tempos, and the like to grow this list to an infinite number of variations to keep you progressing for a very long time.