
No matter what type of exercise you choose to engage in, good posture makes all the difference to your ability to stay on track and NOT injure yourself.
I'm a jogger, so I'm going to use jogging as the example of what I mean.
The easy way to know how good you posture is, is to simply listen to your body. It will tell you very clearly how you are doing. If you are in pain and there is no identifiable cause (such as your knee hurts because you fell down and skinned it) then it's a good bet that poor posture is responsible.
Lets go over a list of common complaints and likely causes.
Sore neck/shoulders - Check your posture. Are you leaning forward? Are your shoulders hunched? Make a conscious effort to straighten your spine and hold you shoulder in a neutral and DOWN position. You'd think that having your shoulders up would help lung capacity but it really doesn't.
Sore lower back - This will be posture related but also is indicative of a lack of muscle tone. To prevent soreness, be sure to stretch out before and after exercising. Also as you jog, move your shoulder forward and back so that there is a slight torso twist form your waist. If you are running like Fred Flintstone (ridged upper body, with only the legs moving) you're going to cause yourself problems that will develop into a larger issue the longer you let it go on.
Knees - The knees are often what people are pained by, or fear being pained by so don't run. the thing is that it doesn't have too. Our bodies are made to MOVE. Do you think someone could have out walked a sabertooth? If your knees hurt you and you don't have a preexisting condition, then it's time to take a hard look at your posture. Chances are, the way you run is causing the problem. Check out where your knee is in relation to your foot? Is it directly over top or off to the side? Does the knee face the direction you're running or is it veering off at an angle? Even a slight variation is going to put unnatural strain on the ligaments will will in turn pull the joint out of true. As with the lower back, proper stretching before hand is key. I would also recommend a light resistance work out for your legs where you can focus on your knee position. Yoga is one option.
Ankles - I haven't heard very many people make this complaint, but as with knees, positioning is very important. If you roll over your ankle, you may not break anything, but you will stress the ligaments and it will take time to get it back is solid working order.
Feet - If you feet are in pain when you run, there are two likely culprits. The first is your choice of footwear. Runners from payless shoes or walmart are just asking for trouble. I know that it can get pricey, but shelling out the money for good quality shoes can make all the difference to your comfort and performance. Good, breathable cotton socks are also helpful. The second is how you run. Most people run heel-toe which is a bad idea. You're giving yourself only two points of contact. Not only are you setting yourself up to slip on uncertain footing, you're creating pressure points. Slow down and try running heel-side-toe. By that, I mean that you land on your heel, roll along the side of your foot and then over onto the balls of your feet and THEN push off. It's a rolling movement that maintain contact with the ground all the way through the step.
Stitches - this one really isn't related to posture, but proper movement can help get rid of the stitch. Belly Breathing. Most of us have learned to suck our stomachs in a breathe with our chests, but when running this will cause you become short of breath fairly quickly. in belly breathing, you extend the abdomen on the inhale and then pull it back in on the exhale. Not only will this increase your lung capacity, but the action of your abdominal muscles will message the stitch and it will go away. This also works for gas and minstrel cramps, whether you're jogging or not.
All of these things are going to take practice to make yourself aware of them. it's not going to happen over night. When you get one, you're likely to lose concentration on another. That's okay! Everyone starts somewhere. Go slow, take your time and get your posture right. The rest will follow.