Mathematical studies show that there is an interaction between a person's heart rate and that person's breath rate. When a person is in a calm state, their heart rate varies rhythmically in synchrony with each inhalation and exhalation. In this case, we say that the person's heart rate and breath rate are coherent, or simply that the person is in a coherent state. In this state, a person achieves higher performance in a variety of mental tasks, as well in tasks requiring coordination of mind and body, such as for example playing golf.
On the other hand, when a person is anxious or stressed, the coherence between their heart and lungs is lost, and becomes chaotic. In this state, mental and physical performance decreases.
The good news is that by using Biofeedback techniques, a person can learn how to gain control of their heart and respiration rates to achieve coherence, thus improving their response to stress, reducing anxiety, and improving performance. Similar effects and benefits can be achieved without computer assistance through training in Zen Buddhist techniques of meditation, but for most Westerners, the computer-biofeedback method is faster.
One component of achieving heart-respiration coherence is by practicing "belly-breathing" or diaphragmatic breathing; however this is necessary but not sufficient to achieve optimal coherence. There are other more subtle aspects, je ne sais quoi that must be learned through experience. This is where biofeedback becomes your instructor, helping your mind to learn to interact with your body.