Intervention
The SOC group followed the recommendations of their primary neurologist or cardiologist for managing the treatment of their symptoms which could include recommendations to increase salt and water intake, physical therapy, medications, and aerobic exercise. One participant in the SOC group had a medication change during the intervention period. Two in this group received an exercise consultation and the same exercise program, but no supervised exercise sessions. One completed physical therapy.The ET group received an in-person exercise consultation and eight supervised in-person or virtual exercise sessions (weekly for the first month and biweekly for the remaining 2 months). Participants completed three aerobic sessions/week, targeting 20–30 min of interval training which started with short durations (3 min) and progressed by increasing working interval and shortening recovery intervals eventually progressing to 30 min of continuous exercise at a moderate intensity. Modality of exercise started on semi-recumbent modalities for most and progressed to upright modalities (upright bike or treadmill) as tolerated. Target heart rate training zones were provided on the basis of the peak heart rate and symptom onset during the maximal exercise test. The general recommendation was to perform the working interval at 75–85% of the individual’s peak heart rate, but monitoring breathing and symptoms were to be the primary criteria used in selecting desired intensity. Participants in the ET group were asked to not make any modifications to their POTS-related medications during the study period, and all complied.Subjects in both groups were asked to track all structured exercise using a chest strap heart rate monitor (Polar, Bethpage, NY) and mobile app (24aLife, Rochester, MN). The research team reviewed each participant’s tracked sessions. An activity load for each session was calculated using the session total duration in minutes and average heart rate for each session as a percentage of the participant’s peak heart rate from the maximal exercise test. The activity load equaled session duration × (average HR/peak heart rate from baseline exercise test). A total activity load for all sessions over 12 weeks and average weekly activity load over the 3-month period were then calculated. This allowed for each session to be assessed on the basis of all factors of activity load (duration, intensity, and frequency) and to make it personalized on the basis of each individual’s measured maximum heart rate. For example, if an individual exercised for 60 min at 50% of their maximum heart rate the activity load would be 30 min, compared to an individual who exercised for only 45 min at 80% of their maximum heart rate where the activity load would be 36 min.