That's a great question. The reality is, whether you are doing a biceps curl or triceps extension, your body doesn't work in isolation.
EVERYTHING is working, just at varying degrees.
A class member recently asked how to "isolate" the triceps with kettlebell training.
The answer is simple: Press, press, press some more.
Oh, and here's the best part: According to some of the leading strength coaches in the field, the triceps are primarily fast-twitch muscle fibers, which means that in order to "tone" them, you need to use heavier weights, which of course means you must use lower reps.
Not only that, the triceps are made up of three parts: the medial head, the long head, and the lateral head. The part that makes your arm look the tightest is the long head and it is best worked heavy from an overhead position.
Good thing we perform our presses with heavier weight and lower reps!
If you look at my arms, they were built off compound exercises, like the clean and press, the snatch, rows, and even squats! You can train yours the same way for similar results.
What's the bottom line? If you want tighter looking triceps, learn how to push your feet through the floor, pull your kneecaps up, squeeze your butt, tighten your abs, power breath, crush the kettlebell handle, and press from the lat. That way you'll use your WHOLE body to make your arms look better and not only that, your entire body will be worked in the process--also proving that you can't work the body in isolation!
See you in class.