In gyms, it's common that someone wants to use the equipment that you are using and you're okay with them using the equipment while you are resting. In English, you could ask "Would you like to work in with me?" In German, I'm not sure what would be an appropriate translation.
"Möchten Sie mit mir zusammenarbeiten?" seems to be the literal translation. But seems more appropriate for a more formal type of 'Arbeit'. Another possibility is "Mit mir traineren?" In real life, pretty much anything would work because people can guess, but I'm interested in learning the German way of asking.