Bike riding is great exercise since it gets you outside into the fresh air, it works your heart and lungs, and many people find it to be easier on their bodies than running. Some people may experience pain in their lower back, upper back, and shoulders, and a lot of it has to do with their bike. Check out these tips to help prevent discomfort:

• Make sure the bike is the right style [1] for where you plan on riding. You don't want to be taking a road bike, that's made for speediness on flat surfaces, out mountain biking. The right kind of bike will support your body better.
• Also make sure it's the right size [2] for you. You'll know it's the right height, if you can stand with your feet flat straddling the bike, and the front bar and your lady business are about two to four inches apart. If you have a women's bike where the bar is slanted, imagine that the bar is horizontal and measure from that line.
• Be sure the seat is the appropriate height [3]. When sitting on the bike, your leg should be almost straight when on the down stroke. Having your knees lock can cause injury and a jarring feeling in your lower back.
• Find a comfortable handlebar height [4]. Start with your handlebar stem one inch lower than your seat. If this position bothers your lower back, you can raise the bars slightly until your back feels good. If you're riding on tough terrain, higher handlebars may be better.
• Don't raise the handlebars so that your spine is in an upright position. A straight back doesn't allow any give when you hit road bumps, and will only make your vertebrae jam together, which will aggravate existing back pain.

Stay tuned for Part Two, all about riding technique and posture.

Source [5]