Take the current mantra of getting fit.
We are admonished to get fit - go to the gym, do some running, take up a sport. Of course, before you take up a new activity, you are advised to have a check-up before you start - getting your blood pressure checked, etc. Yes, it is good advice but I feel that something is missing. I don't think the check-up actually checks on your body - its muscles and posture. Why does this matter?
For a start, if the body is not in balance, then you may be working hard for no reward.
For example, if you already have slightly rounded shoulders, being told to engage your muscles to pull your shoulders back will not change the position of your shoulders.
Why? A simplistic answer is that muscles work in pairs. To actually move a joint, one muscle contracts while the opposite muscle relaxes. This coordination occurs because the contracting muscle "turns off" the opposite muscle. A constantly tight muscle is continually "turning off" the opposite muscle which makes it seem a weak muscle. Until the tight muscle is released and its "turn off" signal stopped, the weak muscle can't respond very well to strength work.
Back to your rounded shoulders. Yes, your shoulders aren't in an ideal position but the problem is actually that muscles in the front of the shoulders are too tight (such as pectoralis major and minor). Until you release the tension in these muscles, you are unlikely to see any change in your shoulder position.
You can work on building up weak muscles but quicker results maybe obtained by stretching and releasing the tight muscles so that the weak muscles then have something to do! You may be surprised at how quickly you see results!
I would suggest that a massage session should be part of your check-up. Developing body awareness is part of getting fit!