Feeling tired and having achy legs can occur due to exercising, overexertion or strenuous walking, especially in hot weather. These symptoms can also be related to medical conditions such as fibromyalgia, peripheral artery disease and Guillian-Barre syndrome, which can require treatment. Fibromyalgia is a condition that has symptoms such as widespread muscle pain, fatigue, sleeping issues, memory problems and restless legs, according to the National Fibromyalgia Association.
Genetic factors can play a role in the development of fibromyalgia. Although there is no cure for this condition, medications can be used to manage many of the symptoms.
Peripheral artery disease, or PAD, occurs when arteries become narrow due to plaque formation associated with arteriosclerosis and causes reduced blood flow in the legs, according to the National Institutes of Health's MedlinePlus. Symptoms of PAD include fatigue, achy legs and pain. Treatment options can include medications for any underlying conditions and surgery for affected blood vessels.
Myasthenia gravis and Guillian-Barre syndrome are two other causes for muscle fatigue or weakness in different body areas, including the legs and arms, notes WebMD.