The Giant Schnauzer is a great athlete. While you may not be able to keep up with them on a run, you can cheat by learning to rollerblade and zoom along beside them or get them trained to pull you along. They will need to listen to your instructions - the most important one is 'stop'. But get them used to 'go right' or 'go left' and you should be in business.
A kiddie collapsible tunnel is all you need for this game. First, you have to teach them how to move through the tunnel, so you may have to crawl through yourself so your dog gets the idea. Time your Giant Schnauzer to see how fast they can get through. Then, have a toy (or a pile of toys) at the end, where your pup has to run through the tunnel, grab the toy and bring it back. This activity will provide a lot of exercise and fun.