Are there any gyms in Darmstadt with monthly contracts? (Staying for 3 months)

Hi everyone!

I'm going to be in Darmstadt for the next 3 months and I'm looking for a gym that offers monthly memberships. I checked out Fitness First but it seems like all their contracts are annual, which doesn’t work for me since I'm only here short-term.
Does anyone know any gyms in Darmstadt where I can join on a month-to-month basis, or even pay-as-you-go options?