By Mayo Clinic News Network

A common cause of back pain is injury to a muscle (strain) or ligament (sprain). Strains and sprains can occur for many reasons, including improper lifting, poor posture and lack of regular exercise. Being overweight may increase your risk of strains and sprains affecting your back.

Back pain can also result from more-serious injuries, such as a vertebral fracture or ruptured disk; from arthritis and other age-related changes in your spine; and from certain infections.

Possible causes of back pain include:

  1. Ankylosing spondylitis
  2. Fibromyalgia
  3. Herniated disk
  4. Kidney infection
  5. Obesity
  6. Osteoarthritis
  7. Osteomyelitis
  8. Osteoporosis
  9. Paget's disease of bone
  10. Poor posture
  11. Pregnancy
  12. Sacroiliitis
  13. Sciatica
  14. Scoliosis
  15. Spinal fractures (especially in older adults)
  16. Spinal stenosis
  17. Sprains and strains

Source: http://www.mayoclinic.org/symptoms/back-pain/basics/causes/sym-20050878