A common cause of muscle stiffness is exercise or hard physical labor of some kind.
Exercise
The most common cause of muscle stiffness is a sprain or strain, which can affect both the muscles and ligaments.
Sprains and strain
Polymyalgia rheumatica causes muscle pain and stiffness. It usually affects the upper body, including the shoulders, neck, and arms. It also commonly affects the hips.
Polymyalgia rheumatica
Insect bites and stings can sometimes cause muscle stiffness. Bites or stings may also cause a red, swollen lump on the skin, which can be itchy and painful.
Bites or sting
Some infections cause muscle stiffness in addition to other symptoms. These infections include:– tetanus, a bacterial infection usually associated with dirt or soil– meningitis, an infection of the brain and spinal cord
Infections
Some medications can cause muscle stiffness. Muscle stiffness is a common side effect of statins, or drugs prescribed to lower cholesterol.