However, there is another important aspect to physical exercise, and it could be just as important as the other two: Motion.
The best forms of motion are the things we associate with young children: Bending, twisting, crawling, leaping, climbing, jumping, stretching and reaching. Anything that gets your body to use all of your joints in their full range of motion. Good posture is essential to this--Imagine trying to do this all hunched over with partially-frozen joints.
Take cycling, for example: It is a great cardio workout and helps condition some of your muscles. However, in terms of motion, it is actually rather poor. You do almost all of your work in a small "box." Your legs go round and round and your arms help provide support.
The good thing about cycling is that it forces you to use your muscles in their intended way. It is harder to get into bad habits and poor form. As a result, cycling has the ability to help your posture. I always get taller when I cycle on a regular basis. It stretches out my back and improves my posture by strengthening my legs in the right ways. So cycling is still helpful, because good posture enables proper motion, but by itself it does not provide adequate motion.
Our 21st century world limits motion. Even in jobs with a heavy component of manual labor, most of the work is done in a limited range. There are few chances to lift your arms over your head or do extreme bending. There are good reasons for this, because those extreme motions is where injuries often happen. But it is also those extreme motions that stimulate health, too.
I have to thank The Egoscue Method of Health Through Motion for many of these ideas. Pete Egoscue is a trailblazer in this movement, and more and more I am finding out that other people are starting to understand the need for general motion in your overall health, too. Some of the healthiest people are not those who do extreme workouts, such as marathons or triathlons. The healthiest people are those who are able to have a regular range of motion in their lives--people who bend and twist and have short bursts of energy rather than long, monotonous workouts.
Some forms of exercise can make me feel stiff. Doing anything in a limited way for a long time can have this affect on you. Even jogging or walking can be poor motion exercises if you barely extend your legs or arms. When I used to run cross country, the best times were when I would loosen up and break out into long strides--my body was very nimble at those points, my legs whipping around and my arms and torso bending and twisting, too--not sprinting, but just a very healthy run. It is a wonderful stimulation for the body to use it this way.
Egoscue's method is very similar to Yoga, although it targets issues that are common in the modern American lifestyle. The goal is to get your body moving the way it was meant to move, and develop the form that will enable that to happen. If you have chronic bad posture, you can't simply change that on demand. Your body has years of habit, tight muscles and other underdeveloped muscles keeping yourself that way. It takes time to work that out, and something like yoga or the Egoscue Method can help you do that. Sometimes you can also improve your posture just by working out on a regular basis.