Asked by: Jason Orben, USA
Although heat should not be used for a fresh injury, it can certainly be beneficial for long-term conditions. Heat patches dilate blood vessels, promoting blood flow and helping to relax painful muscles. Tissue injury activates nerve endings in the skin called nociceptors, which transmit signals to the brain to inform it of pain.
At the same time, neurotransmitters initiate a reflex that causes muscles to contract at the injury site, often to the point of spasm. Fortunately, heat can activate temperature-sensitive thermoreceptors, which initiate nerve signals to block those from nociceptors.
Applying pressure also helps, by triggering nerve endings called proprioceptors. Activating the sets of receptors helps painful muscles to relax.
Dr Emma Davies is a science writer and editor with a PhD in food chemistry from the University of Leeds. She writes about all aspects of chemistry, from food and the environment to toxicology and regulatory science.