The business model of gyms is that people sign up, then stop going after one month. So, that's how gyms stay in business. For the minority who actually use the

The business model of gyms is that people sign up, then stop going after one month. So, that's how gyms stay in business. For the minority who actually use their gym membership, lots don't like running, or have bad knees, so gyms offer a variety of cardio exercises. For example, rowing's a good cardio exercise, and a decent rowing machine is expensive enough that a gym membership can make sense. Running on a treadmill can be preferable to running outside, too. You may not have a good track anywhere close, or you may prefer being able to watch a screen while you run. Gyms offer things like group spin classes, so there's also a social dimension. Ditto the social aspect for meatheads who like to hang out together lifting big weights (no offense intended; I used to be one myself). The other point is that when people say 'fit' they often mean 'skinny'. Unfortunately, the reality is that it's very difficult to lose weight and keep it off (unless you take up smoking, start doing drugs, or get a gastric bypass). Running, in a gym or outside, is unlikely to help. There's some evidence that regular exercise will help you maintain weight loss and it certainly has other health benefits, but this being HN, I think we can be blunt about the fact that if you aren't skinny the odds are against you ever being so in future. > You don't have weights at home, but is bulking up necessary? It doesn't matter if it's necessary or not; some people want to have big muscles or to be very strong, as an aesthetic choice, and they go to gyms for that reason. It's not really much less valid than wanting to be fit. There are reasons to use weights other than "getting big", too. With muscle it's very much "use it or lose it". Older people particularly should be exercising with weights in order not to lose muscle.