It's supposed to be a scientific version of pickle juice, a longstanding folk remedy for runners' cramps.
The theory is that the cramps are a neurological problem, caused by muscle neurons over firing. And the pickle juice - coating the mucosal membranes in your mouth as much as your stomach - supposedly disrupts that.
Anyway, I didn't get a full on case of cramps and had a pretty good finish time - for me.
Did it really work?
I don't really know.
But since it didn't hurt,
I'll give it another go.