Table 4.

Symptoms and tests to assess the disability in myalgic encephalomyelitis/chronic fatigue syndrome objectively

Symptoms	Tests	Ref.
Lack of energy: physical weakness and ”fatigue”	CPET 1: workload and oxygen uptake at exhaustion and at the anaerobic threshold	[62,63]
Cognitive impairment	Specific neuropsychological tests	[64-67]
Post-exertional "malaise”
Physical effects	Repeated CPETs 1, 24 h apart
Cognitive effects	Specific neuropsychological tests
	before and after a CPET or
	before and during a tilt table test
	Repeated neuropsychological tests
Muscle weakness	Examination of the muscles (power, endurance, recovery)	[68-71]
Orthostatic intolerance	Tilt-table test	[72-74]
Defective stress response	Hormonal investigation (HPA axis, thyroid) in rest, at specific moments, e.g., at wakening, and during the day, after provocation, e.g., by adrenocorticotropic hormone and insulin, and in response to an exercise test or psychological stress test	[75-78]
Sleep impairment	Polysomnographic investigation (EEG)	[79-81]
	Maintenance of wakefulness test	[79,82,83]
	Multiple sleep latency test	[79,82,83]
Visual symptoms	Useful field of view tests	[84,85]
	Eye movement tests	[86,87]

CPET: Cardiopulmonary exercise test.