Well, it's been 40 years since Kenneth Cooper wrote "Aerobics," and I feel ambivalent about it.  Cooper's book was seminal, that's for sure, and it introduced a generation to systemic, sustained exercise, but I still talk to people every day who believe that low-intensity, long-duration exercise is the ultimate key to health, fitness, and leanness, and that strength training is for guys who want to build a few decorative muscles on top of that like so much window-dressing. 

In medical school (I'm told), each student does 'rotations', spending some time in each major department of a hospital so as to get a taste of each specialty, hopefully coming out the other side with a some sense of the function of each department and thus, a clearer sense of workings of the body as a whole. 

The last few years have been rather analogous to a med-student's rotations for me:  I got a black belt, I competed in triathlons, I bulked myself up, I did intense yoga, I learned to move like an actor, and, never far from the focal point of my efforts, I lifted metric tons of weight:  quickly, slowly, explosively, diligently counting tempos up and down, with lousy form and with picture-perfect form.  I've hardly explored every possible avenue for exercise, but I've investigated a lot of them that appeal to me.  I suspect I'll keep doing that right until the day I leave this monkey farm. 

There's a lot of great stuff to be gleaned from every discipline I've immersed myself in, but finally they're really very similar.  Stimulate body.  Let body rest and recover.  Get better, stronger, faster.  Move from the back of the class to the front of the class. 

(For me, there's another step, which is, "Get bored, find another discipline, move on."  But I don't recommend this final step.)

If I could disabuse the American fitness-inclined public of one notion it's this fragmentary approach to fitness:  that you work your heart and lungs with one kind of exercise, your muscles with another.  And this or that muscle with this exercise, but this other muscle with another exercise.  And your flexibility or mobility with one move, your neural efficiency with another.

Yes, I'll concede:  wind-sprints will probably build your VO2 max more than yoga, which will improve your soft-tissue extensibility more than powerlifting, which will improve your max strength more than ballet dancing.  But unless you're a professional dancer, yogini, powerlifter, or football player, why should any single one aspect of fitness be more important than any other?  Why not cultivate some degree of mastery over each one? 

Sounds like a tall order, I know.  But I do think it's possible, because the foundation of exercise is simply movement.  Whether you're jogging or doing a yoga asana or lifting a weight or playing pick-up basketball, you are practicing and refining the way you move.  You can do yoga in a way that challenges primarily your aerobic endurance; you can also do it in a way that will challenge and build your muscles, or simply in a way that improves your body awareness.  You can do the same with weight training, running, cycling, swimming, martial arts, Olympic weightlifting.  For the most part, it's not that one activity itself that determines whether it's aerobic or anaerobic--it's the speed, intensity, and duration with which you perform the movements.

I think the reason people stop progressing as athletes--and I'm borrowing Dr. Eric Cobb's use of that term to refer to everyone who moves--is that they stop paying attention.  They start exercising by rote, they stop exploring, and they stop improving. 

Kenneth Cooper's contribution to the fitness industry has been significant; he gave us an easily digestible, bite-sized morsel of an exercise program that was easy to understand.  So hats off to him and to "Aerobics."  Next step:  get people to replace all those hours spent brainlessly on the treadmill with some kind of activity that will actually challenge and stimulate them.