Twin-Peak effect in both cardiac response and tempo of popular music

How the musical tempo affects the performance of heart rate variability (HRV) was studied in this work. By understanding the relationship between the HRV response and the music tempo with decreasing tempo from 140 to 70 beats per minute (bpm) periodically in six successive weeks. There were two groups in the experiment, one was listening drum loop music 3 minutes in the middle of experiment and the other was just rest for 20 minutes. After the processed the information from the objects, the distribution of difference of HRV response between before and after listening various tempo drum loop was similar to the distribution of modern popular music in tempo. Both distributions have the twin peaks about 70-85 and 110-125 bpm.