Lack of physical activity, excessive weight, poor diet, inadequate sleep, and a cold or damp environment are some causes of morning stiffness, according to the National Fibromyalgia and Chronic Pain Association. Morning stiffness usually occurs in people with fibromyalgia, and is seven times more prevalent in women than men.
Muscle stiffness is a condition in which the muscles feel tight and contracted rather than the usual loose and relaxed state. Morning muscle stiffness is often temporary and can be resolved by stretching and physical movement. In some cases, muscle stiffness could indicate a serious issue, such as heart illness, generalized anxiety disorder and Huntington's disease, according to Healthline.