Reason #1 - Injury
It could be from sports or self-accident. Any injuries affecting the ligaments, bursae, or tendons surrounding the joints can give you the pain… and make it hard for you to move.
Reason #2 - Inflammation
Such as Arthritis, Gout, Rheumatoid Arthritis, and osteoarthritis — which you can find out more about this later.
Reason #3 - Aging
When you age, your cartilage tends to tear and wear. This causes all sorts of nasty pain for every time you make a movement.