Proper posture when riding a road bike is extremely important for the health of your back. Many cyclists put in long hours on their bikes--professionals put as many as eight hours a day into their rides--and the physical strain this puts on your back is enormous. It won't show over a short period of time, but in the long run, poor posture can result in back spasms, muscle strains and other complications that might force you off the road. Fortunately, posture is relatively simple--it will just take time for your muscles to adjust to the peculiar form.
Situate your buttocks on the front end of your bicycle saddle. This can be uncomfortable to beginners, but is adjusted to over time.
Position your arms into their holsters, if you have them installed on your bike, or grip the handlebars. Your saddle should be slightly higher than your arms.
Arch your back, particularly between the hips and the shoulders. This gets harder as you get tired and the desire to slouch your stomach increases, but it is crucial to keeping your back healthy. Some individuals with back pain mistakenly believe holding their back straight will preserve its health and improve their nagging injuries, but in reality this will cause unnecessary strain on the back. The curve of your back benefits you in two ways: it improves your ability to pedal and provides cushioning between your spinal vertebrae, protecting them from wear and tear when you roll over bumps in the road.