No, a kidney is not a muscle. While kidneys are located near muscles in the back of the abdomen, and their function is impacted by muscle breakdown products (like creatinine, a waste product from muscle metabolism), they are organs with a completely different structure and function.
Kidney Anatomy and Function
Kidneys are bean-shaped organs responsible for filtering waste products from the blood and producing urine. They play a vital role in maintaining the body's fluid balance, blood pressure, and electrolyte levels. As stated in multiple sources, including the Canadian Cancer Society and My Cleveland Clinic, a layer of fatty tissue, not muscle tissue, holds the kidneys in place against the muscles of the back. https://cancer.ca/en/cancer-information/cancer-types/kidney/what-is-kidney-cancer/the-kidneys https://my.clevelandclinic.org/health/body/21824-kidney
The relationship between kidneys and muscles is indirect but significant. Muscle damage, as explained in MedlinePlus, releases myoglobin into the bloodstream; the kidneys then filter this protein out of the body. https://medlineplus.gov/ency/article/000473.htm High creatinine levels, another byproduct of muscle breakdown, are used to assess kidney function. https://www.kidney.org/kidney-topics/creatinine Muscle wasting, as noted in several studies, is also associated with chronic kidney disease. https://pubmed.ncbi.nlm.nih.gov/20181807/
Distinguishing Kidney Pain from Muscle Pain
It's important to differentiate between kidney pain and muscle pain. While both can occur in the back, kidney pain tends to be deeper and may be accompanied by other symptoms like frequent urination, blood in urine, or swelling. Muscle pain, on the other hand, is often localized and associated with muscle strain or injury. https://www.goodrx.com/conditions/pain/kidney-pain-vs-back-pain