Whole body

Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. RA presents itself most in the wrists and hands but can also affect the feet. 
Foot symptoms in RA can take many forms, including pain in the joints, stiff ligaments, or constant aching. Symptoms are generally worse after a lot of standing, walking, or running. The onset of foot pain is gradual for some people with RA and immediate for others. At some point, though, most people with this disease discover that their foot joint pain makes it very painful to walk. RA can affect the foot in a manner of ways consisting of heel pain, nerve impingements/compressions or certain bunions. 

Arthrosis is a term which describes a non-inflammatory degenerative condition associated with aging. It affects mainly cartilage, which becomes rugged, irregular, and worn out. This breakdown of cartilage can cause pain and loss of mobility of the joint.

Muscle inflammation or Myositis may present itself with weakness, swelling, and pain as symptoms. Myositis causes include infection, injury, autoimmune conditions, and drug side effects. Treatment of myositis varies according to the cause.

Stress fractures are tiny cracks in a bone. They're caused by repetitive force, often from overuse — such as repeatedly jumping up and down or running long distances. Stress fractures can also develop from normal use of a bone that's weakened by a condition such as osteoporosis. Stress fractures may present themselves with; Swelling, pain that reduces during rest, but intensifies during normal everyday activities, the fracture site may be tender and possible bruising may be present.