Music played at 60-80 beats per minute is perceived as most relaxing. Why? The answer may be in a phenomenon called entrainment, the interaction between independent rhythmic processes, such as a musical beat and unregulated heart rate or brain wave frequency.

Christiann Huygens, the 17th century Dutch physicist who invented the pendulum clock, first brought recognition of entrainment to the modern world. Huygens observed that regardless of when they started, the pendulum movement rate of free-swinging pendulum clocks on the same wall synchronized over time. Entrainment has been observed in fireflies that flicker simultaneously, the resetting of body clocks with sunlight changes (circadian rhythm) and in inanimate machine operations. It has been hypothesized that wave interactions cause entrainment synchronization. In the case of listening to music (sound waves entering our bodies through our auditory system), heart rate will move to match ongoing music tempos that we hear, over time. 60 to 80 beats per minute is a calming rate~ a resting heart rate goal for relaxation. And listening to music at this tempo can cause the heart rate move toward the rate of the music.

The sympathetic and parasympathetic nervous systems control heart rate. The rest and digest parasympathetic nervous system correlates with relaxation and a slow heart rate, and the fight or flight sympathetic nervous system relates to excitation and a faster heart rate. Entraining to a slower tempo of 60 to 80 beat per minute relies on parasympathetic nervous system control and can promote relaxation.

But there is more… There are other rhythms going on in our bodies. Neurologists measure brainwaves with EEG studies, and scientists classify brain waves by their output frequency. Alpha waves are defined as waves measured at 8-13 Hz and are indicative of a relaxed mental state~ when a person is awake but relaxed with eyes closed. Alpha wave activity in the occipital lobe of the brain goes along with a relaxed mental state and low arousal. Beta waves measure 13-30 Hz and are associated with a conscious and more attentive state, with eyes open. And faster paced, more activating songs with a quick tempo produce greater beta wave amplitudes. However, some people find faster paced music more relaxing. When I shared “Ai Chi in 3” music (which varies between a moderate and fast-pace) with a class that had been working with slower music for several weeks, one participant said she found the faster paced music to be relaxing, and added the interesting comment, “but I’m Italian and we like fast music.” The personal preference factor.

Studies show that brain waves are affected by music when it is the type of music that the listener prefers. If the listener likes the music, the music tempo influences brain wave frequency, but if the listener does not care for the type of music, the tempo has less of an effect on brain wave frequency. It appears that personal preference for music turns a switch on or off for the ability of music to cause brainwave entrainment. Heart rate and brainwave entrainment may happen~ or may not, with personal preference being the wild card. As is so often the case, “more study is needed…”

And as Jun Kono reminds us, “However it turns out is how it was meant to be.”