A year ago I started doing planks. This is a back exercise in which you position yourself face-forward on the floor, lifting your entire body by your toes and elbows. When done right your back and legs are as straight as a plank. After a minute or two your abdomen and back will feel the strain from holding this pose.
Various people have talked to me about this exercise when I mention my occasional back spasms. Planks are easy to perform, but it took a long time to build up endurance. At first I could only hold the pose for 20 or 30 seconds. I eventually reached a minute. Today, I can hold the pose for a minute and a half. I try to plank at least once in the morning and once in the evening.
About six or seven months into this new routine I realized that my back spasms stopped happening. My spasms tend to be a sharp pain that immediately subsides into a tightened back. I have exercises that reduce the tightness, but my back is wrenched for days at a time. Sitting or getting up with a wrenched back can be painful. However, since planking, these have stopped.
I can only conclude that planking has been the difference in my back and core health. The core of your body governs the back but also your torso (abdominal muscles) and your hips. In other words: posture and mobility. I've stopped regularly doing push ups because I'd rather be rid of my back aches than to have well-defined triceps. I suppose I could do both. Maybe I will.
Bottom line: I recommend a planking routine for those with back aches.