Apologies if this is a really silly question!
I happened to see these tablets in Boots. They are actually for people whose calves cramp during the night, and contain magnesium, vitamin D3, and nicotinic acid.
Nicotinic acid was in chillblain tablets that Boots used to sell years ago. Magnesium, of course, is supposed to be good for muscle tension, and we all know about vitamin D. My unscientific mind is thinking that perhaps the magnesium would relax the muscles, and the nicotinic acid would send the blood through the muscles...the information talks about muscles being knotted and the muscle fibres being crushed together. The pack actually shows a rope with a knot in it!