Electrotherapy, massage and infrared rays can stimulate local or systemic blood circulation in a reflective way, and accelerate nutrient supply and waste excretion. There is no profound theory.
However, massage methods have existed since ancient times, and there are many theories in this respect, mainly the meridian theory of traditional Chinese medicine. There are still credible.
There are also psychological effects on users, just like placebos. However, it is best not to let users know about it. After all, knowing magic, watching a performance won't have that effect. But in view of the fact that many people use this psychological effect to engage in pseudoscience and fool the public, let's talk about it here, hehe.