In regards to the staff report Does massage work by getting rid of toxins?, there are more systems in the body than just muscles that need to be factored in.
Pain from working out can be tracked to at least 2 factors: excess water, and crystallized waste product. Waste products in muscles are mainly salts and acids; uric acid for one, and calcium as another. Muscle cells are like magnets, with the opposing ends facing in. When a muscle cell contracts, calcium bridges the gap and binds the ends together. For a muscle cell to relax, there has to be enough energy in the surrounding cell to break that calcium bond back open. If there is not enough energy in the surrounding cell, due to exhaustion, then the calcium bond stays, and the cell will not decompress. If this happens to enough of these single cells in a small area, that becomes a trigger point, or “knot.” A massage therapist adds energy into the cells, by compressing against the bonds, and breaking those calcium ties. The excess calcium needs to be carried out through the circulatory system.
Working out definately increases blood flow to and from muscles through the circulatory system, but muscles that remain tensed can impede the flow of waste products back through the lymphatic system (which carries 10% of the plasma out of the muscle fibers.) One can therefore assume that a lot of the pain associated with body-building has to do with muscles being full to the brim with excess water and plasma, which massage helps to flush out by basically squeezing it back into circulation, through both the lymphatic and regular ciculatory system. Massage also induces full-body relaxation and helps you tune in to deeper, more powerful breaths, that in turn help to pump wastes through the lymphatic system, which then dumps back into the circulatory system and out through the kidneys and urine.
The kidneys work by comparing filtered blood to unfiltered blood. If there is more sodium in your unfiltered blood, it will filter some out until they’re about even. If there’s more calcium in the already filtered out waste fluid, it won’t take any more out of your blood.
Ultimately, increased cirulation means increased metabolism. Nutrients are delivered faster, and “wastes,” being broken-down cellular building blocks, are picked up and filtered out just as quickly. If you don’t increase your water intake to help carry out the temporary excess caused by a massage-induced metabolism spike, then there’s only so much water to absorb and carry out the sodium, calcium, etc. Which means that you’ll have more in your blood than normal, and that overloaded blood flows straight back into your muscles fibers. Excess salts form crystals, which then cause more pain and stiffness.