Kidneys — The kidneys are a matched pair. One painful kidney can cause back pain on one side or the other. Kidney pain can feel like back pain, and may occur on only one side. It is usually quite lateral, and just barely low enough to qualify as “low” back pain. However, when kidney stones descend through the ureters, they can cause (terrible) pain in the low back. Kidney stone pain is often so severe and develops so rapidly that it isn’t mistaken for a back pain problem.
Tight hip flexors occur for a variety of reasons. Those who run frequently or engage in other activities that put strain on the hip flexors are likely to experience hip flexor tightness at one time or another. A blow to the hip or poor conditioning can also be causes of tight hip flexors. These causes can usually be attributed to tiny tears that occur to our hip flexors through rigorous activity.
You can strain or tear one or more of your hip flexors when you make sudden movements such as changing directions while running or kicking. Sports and athletic activities where this is likely to occur include running, football, soccer, martial arts, dancing, and hockey. In everyday life, you can strain a hip flexor when you slip and fall, for example.