Table 1. Classification of altitude levels (modified from [3]).

Altitude level*1	Remarks
Near sea level (0–500 m)	No altitude-related problems
Low altitude(>500–2000 m)	A mild limitation of aerobic performance capacity is demon‧strable, particularly in well-trained individuals No additional problems in stable patients *2 engaging in the ‧same physical activities as at sea level
Moderate altitude(>2000–3000 m)	Threshold altitude for acute mountain sickness; usually no danger of HACE or HAPE; acclimatization is important for ‧optimal performance capacity Generally well tolerated by patients *2with stable disease and adequate reserve performance capacity; restrict activities over the first few days and ascend slowly above 2000 m; ‧beware of contraindications (Box)
High altitude(>3000–5500 m)	Acclimatization important to prevent altitude sicknesses; ‧marked limitation of performance capacity 3000–4000 m: even stable patients *2 with good performance capacity need thorough evaluation beforehand >4000 m: generally inadvisable for patients *2
Extreme altitude (>5500 m)	remaining at this altitude leads to progressive physical decline (loss of performance capacity, catabolism) short stays only for healthy, well-trained persons

^*1 Terminology recommended by an international expert panel (3)

^*2 Patients with cardiovascular and pulmonary diseases that may worsen under hypoxic conditions