This study has been cancelled due to the pandemic and we are planning on starting a similar study hopefully next year.

Postural orthostatic tachycardia syndrome (POTS) is a disorder of unknown origin characterized by orthostatic intolerance and increased heart rate (HR) of ≥ 30 beats/minute during orthostasis in the absence of orthostatic hypotension. In addition to the orthostatic intolerance and tachycardia, patients with POTS experience several debilitating symptoms including light-headedness, nausea, blurred vision, fatigue, mental confusion ("brain-fog"), chest pain and gastrointestinal problems. Several potential underlying mechanisms have been suggested for POTS including autonomic denervation, hypovolemia, hyperadrenergic stimulation and autoantibodies against adrenergic receptors. However, none of these proposed mechanisms has yet led to an effective treatment. Physical activity is recommended as a complimentary treatment in POTS in international guidelines. However, less is known regarding how physical activity could successfully be implemented in clinical practice in patients with POTS. Thus, in the current study, we aim to assess the effect of a 16-week specialized physical activity program in POTS.

A total of 100 patients diagnosed with POTS are asked to participate in the study. Prior to start of the training program a special POTS questionnaire (based on the symptoms reported in The BIG POTS Survey), the orthostatic hypotension questionnaire and SF-36 (general health questionnaire) will be completed by the participants. Orthostatic tests are performed during 10 minutes, measuring heart rate and blood pressure after 0, 1, 3, and, if possible, 10 minutes of standing. On a separate occasion, patients will perform a submaximal biking exercise test, while noting symptoms, degree of exertion, achieved effect, pulse and blood pressure reaction. Following this initial evaluation, the training program will be performed during a total time of 16 weeks, which may be non-consecutive but within 6 months in total. The training program consists of 2-3 visits per week, and 60 minutes per visit. The training may be performed on specialized exercise bicycles in supine position or upright position depending on the severity of POTS symptoms. These exercises will be done under the supervision of physiotherapists with special interest in POTS. After the final training session the POTS questionnaire, the orthostatic hypotension questionnaire and SF-36 will be completed once again. In addition, orthostatic tests and submaximal biking exercise test will be performed on a separate occasion soon after the last training session. The present study will be using longitudinal comparisons, meaning that the 100 POTS patients are their own controls. The POTS questionnaire, the orthostatic hypotension questionnaire, SF-36, hemodynamics and exercise capacity will be compared before and after the 16-weeks training program.

Inclusion Criteria:

• Patients diagnosed with POTS who have given written informed consent for participation in the study.

Exclusion Criteria:

• Patients with myalgic encephalomyelitis are excluded from the study.