Since human consciousness seems to inhabit bodies, bodies which evolved in certain conditions, it makes sense that exercise should be one of the chief activities of human life.
The fact that exercising is not a constant part of virtually everyone's life indicates a society very out of touch with reality. To see exercise's immense importance takes only minimal common sense. To experience exercise's benefits requires only that one be open to experience.
Walking is probably the most basic and important human exercise. It is totally underrated and underutilized. I suspect that it is probably difficult to really be in good health mentally or physically without a substantial amount of walking, year round. I suspect that there are many biological processes in our bodies which require walking as a catalyst. Walking should be integrated into as many aspects of daily life as possible, like walking to get groceries, walking to work, or parking at a distance from a restaurant and walking the rest of the way. I suspect that running injuries would diminish if one always walked at least as many miles as he ran.
I have heard that lifespans are longest in regions of the world where incidental exercise is part of ordinary lifestyle.
Simply doing plenty of fast walking will result in pelvic girdle muscles similar to those found in most classical athletic statues.
It would be wise for one to practice both Western and Eastern exercise systems. Tai Chi, other martial arts, and Hatha Yoga are examples of Eastern systems. Among other things, they teach that certain kinds of strain are unhealthful. Practitioners of some of these systems seem to age with much more vitality than other people. Note the coiled spring, Tai Chi like, spiral energy of the Greek statue above.
I suspect that aerobic exercises (swimming, biking, running, walking, etc.) do us the most good, as far as Western exercise goes, and that one should religiously engage in some strenuous aerobic exercise in addition to much walking. However, I think that it is difficult to have running be one's principle life long aerobic exercise, on account of the strain it puts on various body parts. I suspect that we are each given a certain allotment of years in which to run a lot, and that different people use up that allotment at different periods of their lives.
Exercise is such a sacred self-duty, that much or most it should be a personal, not a group activity. Habits involving only yourself should be formed. Don't become dependent of your wife exercising with you. Do not let exercise classes or competitive activities become your exercise core. It is unfortunate that in European/American culture, exercise is often associated with mere competition. People whose physical activity is based on competition (sports), tend to become the most unfit later in life. Exercise for self-perfection is an infinitely worthier activity than mere competition.
The most important issue with exercise is developing discipline.
This can be done by starting out with such an easy program (running 3 blocks every day), that lack of discipline itself is the only possible obstacle. Since exercise should last your entire life, you've got years to increase the amount of exercise (how far you run, etc.). It is probably best to start with a daily program that is easy, and to stick to that program NO MATTER WHAT HAPPENS. That means you run 3 blocks if you're really sick, if there is a four foot snow cover, etc. You get the idea.
You should build up super slowly! 99% of your body parts might adjust to some increase, but that other 1% might be a tiny body part that becomes a show stopper.
If you fail to develop discipline, all is lost! Once you REALLY develop discipline, something inside you gels permanently, and you'll be able to skip occasional days without losing the lifetime commitment.
A second principle (which applies only to somewhat strenuous aerobic exercises) is:
You only get to stop ONCE, when you're all done.
Practicing this principle teaches you to pace yourself, and instills the mindset of continuity. Eventually, you go farther and farther by stopping only when you're all done. A corollary of this you only get to stop once principle is that if you're running, and you come to a red stoplight, you don't do a cute little running in place. There is ALWAYS some direction you can keep running in, and there will certainly be an eventual way to get across that street and back onto your intended path, without breaking your stride.
Exercise, like preventing fat accumulation, requires unremitting vigilance, one can never rest on his past workout accomplishments. Since the human body has limited ability to store the results of exercise, the exercise that matters most is what you've done in the last week, not years ago.