Weakness is when there is a decrease in strength in one or more muscles. This is also known as asthenia where the body feels fatigue or tired. This can lead to situations where the person may not be able to move a certain part of body properly. Weakness can be caused by the flu, thyroid disease, depression, lack of sleep and etc.

Some symptoms include delayed or slow movement, uncontrollable shaking, muscle twitching and muscle cramps.