POTS patients seem to experience orthostasis-dependent muscle weakness and pain as well as increased muscle fatigue upon physical activity, which can be improved by regular aerobic exercise. However, reduced sweat production of the extremities with limited control of the body temperature leads to exercise intolerance, so that sticking to a training program becomes a challenge for most patients. Recordings of MVRCs provide a new tool to assess muscle membrane dysfunction, depending on ischemia, surface temperature and training. As muscle dysfunction is assumed to be present in the majority of POTS patients but has not yet been scientifically studied the present study aims at understanding the muscular and cutaneous functioning in POTS using MVRC recordings, dependent both on orthostatic stress and exercise training as well as body temperature regulation. Our main hypothesis is that POTS patients experience functional muscle dysfunction that may be linked to altered muscle perfusion or body temperature regulation.

The purpose of this study is to examine muscular and cutaneous dysfunction in POTS in order to i) better understand the underlying pathology for symptoms and to ii) ultimately improve treatment options.

POTS patients seem to experience orthostasis-dependent muscle weakness and pain as well as increased muscle fatigue upon physical activity, which can be improved by regular aerobic exercise. However, reduced sweat production of the extremities with limited control of the body temperature leads to exercise intolerance, so that sticking to a training program becomes a challenge for most patients. Recordings of MVRCs provide a new tool to assess muscle membrane dysfunction, depending on ischemia, surface temperature and training. As muscle dysfunction is assumed to be present in the majority of POTS patients but has not yet been scientifically studied the present study aims at understanding the muscular and cutaneous functioning in POTS using MVRC recordings, dependent both on orthostatic stress and exercise training as well as body temperature regulation. Our main hypothesis is that POTS patients experience functional muscle dysfunction that may be linked to altered muscle perfusion or body temperature regulation.

The purpose of this study is to examine muscular and cutaneous dysfunction in POTS in order to i) better understand the underlying pathology for symptoms and to ii) ultimately improve treatment options.

The study includes two examination days with the same procedure for all participants. In between the examination days, participants will undergo an endurance training protocol for 14 days. The first examination day takes place in two parts: Participants will first receive repetitive MVRC recordings of the right tibialis anterior muscle (TA): 1) before, during and after repetitive stimulation of the right TA (intermittent 20Hz for 10 min) in the supine position. Then MVRC recordings will be done from the left TA 2) in the supine position and during the 60° HUT upright position for 10 minutes. The duration of this first part is approximately 60 minutes. The second part consists of a TST of the hands and feet only, including a SWT on the index, middle and ring finger of both hands. This second part also lasts about 60 minutes. On the second examination day, the first part (only 1)) of the first examination day will be repeated. In between the examination days training sessions will be undertaken on days 1, 3, 5, 7, 9 and 11 between the examination days. Participants will be asked to contract their TA muscle repeatedly by pulling the right foot towards the head in a standing position while the heel remains on the ground (at 5 second intervals). In order to carry out the training they will also receive a video demonstrating the exercise. On days 1 and 3 they will do the exercise for 5 minutes, on days 5 and 7 for 10 minutes and on days 9 and 11 for 15 minutes.

Inclusion Criteria Patients:

• Informed consent as documented by signature
• Patients with diagnosed neuropathic POTS
• Age: ≥18 years and ≤ 60 years

Inclusion Criteria Healthy Volunteers:

• Informed consent as documented by signature
• Age: ≥18 years and ≤ 60 years

Exclusion Criteria Patients:

• Pregnancy and breastfeeding
• Inability to adhere to the training protocol

Exclusion Criteria Healthy Volunteers:

• Pregnancy and breastfeeding
• Intake of vasoactive medication or known, non-treated arterial hypertension
• Inability to adhere to the training protocol