I'm surprised you haven't heard of it, it's been around years. I believe it came from horse racing, where it's called 'milkshaking'
https://paulickreport.com/news/ray-s...0the%20muscles.
Last time I checked it was legal. And don't mention it to Graham, but I've tried it in my middle-distance track racing days, having read a report that Fausto Coppi used it (er, amongst other things)