Yes, I get it too.
I've had DBS so I only get a fraction of the dystonia in one foot in particular when I'm working out at the gym still but it can be painful enough to stop.
I find now if I pause for a minute or two and massage my foot it helps whereas before I had surgery it got to the stage where it meant I was well and truly off and in need of a Sinemet.
Perhaps try stopping and massaging it till the dystonia subsides and if that doesn't work upping the Sinemet by say half a tablet before you work out?
Cheers,
Lee