Imagine lifting something very heavy. Take a deep breath and lift the object by pulling and grunting. Suddenly you feel this stabbing pain in your lower back and also down your buttock and thigh that takes your breath away. The pain is so strong that you can't get up. Walking and moving is extremely painful.
What happened?
What has happened is that you have (unconsciously) recruited your diaphragm to lift the weight. This thing happens very often when lifting heavy objects, but it can also happen when you have a stiff back and perhaps, thrown into extremely comfortable but extremely anti-functional positions on a sofa or bed, and you suddenly try to change position.
The diaphragm attaches to the sternum, the last 6 ribs and the lumbar spine. It has fibers that attach to the same structures on which the psoas major, quadratus lumborum, oblique abdominals, intercostals, etc. are anchored. The diaphragm is a powerful muscle and not designed for lifting objects, but for breathing. When it goes into spasm, it can pull on structures so severely that it forces them out of their ideal position. This produces spasm in many other muscles (those mentioned above) that are anchored to the same structures as the diaphragm. Suddenly, like a domino effect, this affects the entire body. For example, the psoas major is a very powerful hip flexor. In fact, when it goes into spasm it keeps a person excessively bent forward. In the same way, due to this strong chain traction effect, the compression can easily increase precisely between those lumbar vertebral segments which are already rigid or not optimally functional and very often, the famous 'tweezing' of nervous emergencies can be carried out, which they create those very annoying radicular symptoms called neuralgia.