In general, massage increases the flow of blood through muscles. This blood flow can pick up metabolic debris that has been left in the muscle and surrounding tissues from contracture or overstretching of the muscle. Some therapists may refer to this as “toxins” for the sake of simplicity. I don’t love that word as it seems a bit permanent to me. But yes, there is metabolic waste that is not wanted within the body that does start to circulate again once it has been released from what was holding it. The best way to remove it is to drink plenty, plus more, water and release it out of the body through urination.