Exposure to stress alters the activity of the adrenomedullary, adrenocortical and sympathetic nervous system, depending on the type and intensity of the stressor. Physical exercise represents a stress condition influencing many systems in the body. Given a workload of at least 70-85% of Vo2max, exercise is a potent stimulus of the hypothalamic-pituitary-adrenal (HPA)-axis. The increased endogenous cortisol secretion results in important metabolic and cardiovascular effects to maintain cellular and organ homeostasis. Patients with Addison's disease are not able to meet the increased demand of adrenal steroids in case of physical exercise, which may result in an impaired exercise capacity and a prolonged post-exercise recovery. We hypothesize that a hydrocortisone stress dose increases exercise capacity and improves post-exercise recovery in patients with Addison's disease.

Inclusion Criteria:

• Addison's disease
• 18-50 years
• stable glucocortiocid replacement therapy

Exclusion Criteria:

• Presence of intercurrent (acute) infectious disease
• Mental impairment (major depressive, anxiety, panic, adjustment, bipolar, psychotic, posttraumatic or borderline personality disorder)
• Presence of the following chronic diseases: diabetes mellitus, chronic obstructive pulmonary disease, renal failure, chronic anaemia, malignancy, rheumatoid arthritis
• Presence of the following cardiovascular conditions: unstable angina pectoris, history of myocardial infarction, uncontrolled cardiac arrhythmias causing symptoms or hemodynamic compromise, symptomatic (severe) aortic stenosis, uncontrolled symptomatic heart failure, acute myocarditis or pericarditis, left main coronary stenosis, moderate stenotic valvular heart disease, tachyarrhythmias or bradyarrhythmias, hypertrophic cardiomyopathy and other forms of outflow tract obstruction, high-degree atrioventricular block
• History of pulmonary embolus or pulmonary infarction
• Known aortic aneurysm
• Severe hypertension (>170/100 mm Hg)
• Medication that affects cardiovascular function (beta-blocker, calcium antagonist, ACE-inhibitors, aldosterone-antagonists)