There is nothing simple about 'simple' back pain. It is a mixture of factors. The latest research suggests these are some of the main reasons for back pain:
We still don't know all the reasons why some people get lower back ache and others don't - although we do know that most people will get it at some point in their lives.
Genetics and Hereditary - Same of the newest research findings are pointing more and more at genetic or hereditary reasons. Your genes and your family history may influence how your spine ages and whether your disc's degenerate early.
Ageing and Disc degeneration - although this is entirely normal ageing tissues may not be able to move and support the spine as well as they did when they were younger. Your back might be less able to cope with daily postural demands and this may lead to other tissues taking up the strain a little and becoming sore.
Strained facet joint. Pain and spasm in the back muscles may accompany this as these may tighten up in order to support and protect a sore joint.
Muscle spasm - this is a common symptom of lower back ache but it usually is in response to something like a strained joint or ligament or because the tissues are stressed by positions that make them feel sore.
The nervous system - Sometimes there is no tissue injury at all, or it has healed up long ago, yet we still continue to experience symptoms that are driven by our nervous system generating painful sensations.
Very often all these different things add up and together. Because this condition is a mixture of overlapping problems it is not always clear exactly which tissues are causing the problem.
This type of back problem occurs when your spine struggles to cope with the demands and strains of daily life. The human spine is a strong structure, perfectly designed for the job of protecting our spinal cord and allowing movement.
Usually it is a combination of these things that causes the problem.
The following diagram helps to what happens over time as the body becomes less able to cope with daily demands.
Small daily postural demands add up over time.
This diagram shows how it can break through a threshold and cause backache
This explains why sometimes very small things cause us to feel discomfort and why postural demands are one of the key reasons for back pain. It makes little difference if you are working in an active manual job or whether you are in a sitting down office job. It seems that staying in any position for too long can make your back feel sore, so its less about what the position is and more about the time spent in it.
If you have poor fitness you will have poorer muscle tone and poorer circulation. This will affect the amount of support your muscles give your spine and will slow down the healing process.
Surprisingly, being moderately overweight is not one of the main reasons for back pain. If you are very overweight however, you may be more likely to get backache. I think generally if you are overweight you are probably less fit - and its this loss of fitness which leads to the problems mentioned above.
Poor diet affects the health and healing of the tissues
Smoking has been shown to cause significant changes to the circulation in the spine, especially the discs, and is linked to increased back problems.
So, in summary, if you very overweight, have a poor diet and smoke you are more likely to have back problems.
All these different things play a part in causing this condition which is why it is impossible to treat it by addressing just one thing.
Balagué, F. et al., 2012. Non-specific low back pain. The Lancet, 379(9814), pp.482–91.