If you use exposure compensation, have the lab develop the film normally. If you don't, tell the lab you shot it at an EI of 100. A good B&W lab should have no problem developing an ISO 125-200 speed film this way, but an ISO 400 film will be decidedly hit or miss.
If you want to photograph a man spinning, give some thought to why he spins. Understanding for a photographer is as important as the equipment he uses. - Margaret Bourke-White