Weakness
Weakness is a symptom that can help your doctor narrow down what disease you may have that is causing the symptom. Weakness is a lack of physical or muscle strength and the feeling that extra effort is required to move your arm, legs or other muscles. If the person is able to make their muscle work but it hurts is also a sign of muscle weakness. Muscle weakness could be caused by another problem such as low levels of electrolytes such as sodium and potassium, infections as in a respiratory infection, a problem with the thyroid gland, which regulates the way the body uses energy, Guillain-Barré syndrome, or myasthenia gravis.
source: www.webmd.com/a-to-z-guides/weakness-and-fatigue-topic-overview
