It is a good catchy name. I agree it should fetch high xx at a bare minimum from a reseller.
The hard part for me to appraise is its top value. It really will depend on what an end user would use it for. If a national chain of gyms like Ballys or Virgin wants to buy it for a new marketing scheme, you could get mid xxx to low x,xxx for it. My guess is that you will have a hard time getting companies like those interested. If a smaller gym wants it, I could see you getting $150-300 for the domain.
this is a smart name to have! either developed or undeveloped you will get a positive sale on this one, would estimate sim to fonzie with a minimum mid $xxx
....a very good snatch!