Heart Rate Variability-Guided Exercise Intensity

Although all participants will daily measure their HRV, only in this intervention group each day's results will influence their exercise intensity. From the outcomes reported with smartphone photoplethysmography, explained the measurement process in the outcomes part, the root means squared differences of successive RR intervals (rMSSD) will be chosen as a reflection of vagal activity to prescribe the workout intensity [50 (link)]. In this regard, the natural logarithm of rMSSD will be calculated to make parametric statistical comparisons assuming a normal distribution. For establishing the training intensity and load, a 7-day rolling average measure (LrRMSSD7day-roll-avg) will be utilized. Subsequently, the scoring obtained will be contrasted in the smallest worthwhile change (SWC) to analyze if the daily result is inside SWC upper and lower limits, calculated as LnrMSSD reference week mean ± 0.5 × SD [51 (link), 52 (link)]. The reference week of the first 4 training weeks will take the limits created in the baseline week, and in the rest of the program, an updated measure will be carried out every 4 weeks with the SWC for the past 4 weeks, because of the influence of exercise in participants cardiac autonomic modulation [53 (link)].
In this regard, when the daily LnrMSSD fell inside the limits created by the SWC patients will perform high-intensity training characterized by a cardiovascular intensity from 80 to 95% of their reserve HR (increasing a 5% every four weeks) and a weighting load from 70 to 85% of their RM (increasing the load 5% ever mesocycle, four weeks). Whereas if any day patients’ scoring fell out of the SWC, they will train at the same intensity as the PEG (Fig. 2).Fig. 2

Intensity progression and intensity decision making process for the high-intensity exercise guide by HRV group