Lower back-pain can be a pain in the arse (hips, neck, spine, etc). But what happens when your back flares up and feel stiff, sore and immobile? You stretch it, right? Guess what? You probably shouldn't be stretching your back. Why? Allow me to explain.
By now you should have cottoned on to the fact that exercise is really important for your health, so important that it really ought not to be an option for you. Cardiovascular exercise, as the name suggests, develops the cardio (heart) and Vascular (circulatory system). But it works on the respiratory system (lungs) as well. In other words, if you want a healthy heart, lungs and arteries you should do some cardio, which means getting out of breath for prolonged periods of time. Cycling for example.
Whether you are sedentary for most of the day or a highly active person it is possible to develop back pain. If your pain isn't the result of a specific injury but is the kind of pain your doctor may term "non-specific" then you need corrective exercise.