Before revision:  We relate these changes to the exercise intensity quantified by the heart rate . Beyond a certain intensity threshold, RRI's show strong short-time anticorrelations on different scales, for which we propose a physiological interpretation in terms of hemodynamics. The results demonstrate the feasibility of dynamical statistical analysis of RRI's to monitor cardiovascular exercise conditions in real time with wearable devices and without previous knowledge of external parameters such as the maximum heart rate of the individual .
After revision:  We relate these changes to the exercise intensity quantified by the heart rate (HR). Beyond subject-specific HR thresholds the RRIs show multiscale anticorrelations with both universal and individual scale-dependent structure that is potentially affected by the stride frequency. These preliminary results are encouraging for future applications of the dynamical statistical analysis of RRI's to monitor cardiovascular exercise conditions in real time with wearable devices and without previous knowledge of external parameters such as the maximum heart rate of the individual .