As Alexykidman says, no small business, especially a gym, is going to be a booming success with the economy the way it is now. Be careful!
Although I've never owned a gym, I've owned other small businesses in the Los Angeles area. The fundamentals are the same whether it's a gym, a car repair shop, or a grocery store. The hardest part is to know that you can't expect to take home any money for the first year or two, unless you have enough money up front to get it strarted without loans to repay. Knowing that going in, you can look forward to getting profitable after the first couple years, and then if you do things right, it can be a lifelong decent income. If I were to open a gym, the first thing I'd do is find one that is just going out of business, and try to buy out their machines & equipment, and maybe, depending on their membership, try to lure some of their clients to your new place by giving a special, or honoring their old memberships if the old gym is gone bust, and they lost their money. That way, you get equipment at pennies on the dollar, and built-in members.
What would scare the sh*t out of me would be to either borrow a huge amount of money to buy new equipment, or to use up all your savings, etc., to start the gym with about $10 left to your name. At least if you start out with used equipment, and maybe a short-term lease on a building, you could get out of it safely after a couple years without owing $10s of $1000s on stuff you bought new, but is now used and worth a fraction of what you owe on it. You need to either have enough money on hand to pay all your bills for awhile, or keep another job until the gym gets going on it's own. Too many people lay out their whole life savings, and borrow against everything but their underwear, then lose it all becuase they can't keep things afloat while the new business is still shakey and not paying it's own way yet.
And then you need to figure out how many people you want to join, and how many people are in that area who might join. That's a hard thing to do, but companies like McDonald's will spend more in marketing research to check out an area than it might cost them to just stick a new restaurant in place.
Another thing you could do to "test the water" is to do what my friends are always trying to railroad me into... I have a decent gym which I built at home, and you could do something like that and see how many people would show interest in coming on a pay basis. Mine is too small to do that, but you could easily do it if you have a 2-car garage, or a big bonus room or basement. I have every machine that a gym has, and all high-end names. I got it all from gyms that went belly-up, and from millionaires who buy this stuff and never use it, then get tired of looking at it.
Just my thoughts...
Charles