What advantage is there in: jogging, biking or whatever fad exercise is popular this month over: tilling a field, hauling compost or scything hay for livestock? If you answered "there is no advantage" then you and I are on the same page, Hommie. In fact, if you were to spend your doctor-recommended hour a day in the field, you'd probably contribute enough to grow everything you would eat on a vegetarian diet. Animals are going to require a little more work than an hour a day per person but that is a tangent for a different post. The truth is that growing fruit, vegetables and grains, even by hand, is not as labor intensive as you probably imagine it is.
I'm not comparing farming to martial arts or weightlifting for instance. Spading a field is not going to make you a trained deadly weapon or a beefcake MoFo, but it will fulfill your daily cardiovascular exercise requirement in a much more practical way than say: Tai-Chi, Tae Bo or Tying your shoes (see what i did there?). So practically speaking, pounding the pavement for an hour after work to stave off heart disease, aside from being boring, is an inefficient waste of time.
Why does Average Joe prefer "exercise" over "labor" then? My best guess is that it is an insidious form of conspicuous consumption. Poor people engage in "labor" while us high-class folks buy food from the store, send our kids to daycare, shit in our drinking water and "exercise" after our busy, fulfilling and productive day of pushing paper. My second best guess is that the idea just doesn't occur to the average lemming.
Can a tractor rototill a field faster and more easily than you could spade it? Do chemical fertilizers require less labor to apply than compost? Does preemergent herbicide keep a field weed free more easily than a scuffle hoe? Well, my dear Watson, sure as a bear shits in the woods and my dogs shit all over the otherwise soon to be harvested brassicas modern farming requires far less labor. But are these methods anymore "efficient" when 98% of us pound pavement instead of flipping soil? Quit drooling. It was a rhetorical question.
When you get bored of paying gym membership so that you dont keel over from heart disease at the ripe old age of 20, i'll have a spade and an extra pair of work boots with your name on them, my friend. We can "exercise" together and sustainably.