In recent years, researchers have begun to watch in more detail the symptom of fatigue, which exists frequently in chronic conditions and has a negative impact on the functionality and quality of one's life. Fatigued is believed to be multidimensional in nature and factors that contribute to its appearance include muscle weakness, pain, anxiety and disturbed sleep . Some chronic conditions, in which fatigue appears, beyond Chronic Fatigue Syndrome, are described below:
Cancer and chronic fatigue
Chronic fatigue is one of the major symptoms occurring in patients with cancer [2,3] and it has been found to be the most common marker that affects the quality of life of the person living with cancer . Exercise improves fitness in people with cancer [5,6], their general health , reduces fatigue  as well as depression [5,7] and increases happiness .
Stroke and chronic fatigue
Fatigue after a stroke is a common symptom, which may persist long after the episode.  It can appear to up to 70% of patients [8,9], but often remains "invisible". This symptom is not the same as that of tiredness, because frequently it appears without warning and it does not leave with rest. Factors affecting fatigue are muscle weakness, sleep, pain, medication, depression and difficulty in speaking [8.10]. Fatigue in turn can adversely affect life expectancy .
Multiple sclerosis and chronic fatigue
Fatigue is the most common and one of the most debilitating symptoms in multiple sclerosis (MS) [12,13]. Although the onset of fatigue in MS is not fully understood, it is thought to be multifactorial and to be affected by changes in the immune and nervous systems, sleep problems, changes in the circadian rhythm and depression .
Rheumatoid arthritis and chronic fatigue
Patients with rheumatoid arthritis often have fatigue, which as they state upsets them and creates anxiety and has a significant negative impact on their lives. They cite that they cannot manage fatigue and they do not have enough support from health professionals who believe that they cannot deal with it and as such leave the patient to cope alone .
Fibromyalgia and chronic fatigue
Often patients with fibromyalgia have severe fatigue, which reduces their motivation to do activities, extends the time of the activity, hinders concentration and memory  thus affecting their lives.