Heat helps your body heal by relieving pain, relaxing tight muscles and tendons, and essentially sedating your sensory nerves. Additionally, it speeds up your metabolism, opens up your circulatory system, and increases blood flow and oxygen to the injured area.
This increased blood flow helps oxygenate and detoxify your body and supports cellular nutrition, all of which can help speed healing and repair damaged tissues. Fluidotherapy units are often used to apply heat therapy in a medical setting, which works much like a whirlpool but with a dry medium instead of water.