If you are a fond proponent of going to gyms, that is great. While far too many people in our world do not do very much to make themselves more fit and healthy, you are among the relatively rare few people who take their personal fitness seriously enough to actually do something about where it is right now (probably not as great as you would ideally want it to be). Of course, just because you go to the gym and push yourself beyond your comfort zone is not necessarily the be all end all that some folks imagine that it is. Whether you realize it or not, you can do even better than that, if you really want to push yourself a little bit further. For instance, you have the power to do a lot of the exercises that you would normally be doing in the gym, only without having to go there.
For example, have you ever stayed at home and done a circuit of different exercises in your living room. All you have to do is establish what you are going to do (say, a set of pushups, a set of squats, a set of lunges and a set of situps), determine how many reps and sets you want to do (say four sets of 25 reps apiece), and get to them. You do not necessarily have to train as if you are about to join the Navy Seals. You might only be working to make surethat you stay healthy and strong.
The great thing about training in circuits is that it conditions your muscles to be able to go longer. Keep in mind that the most important muscles in your body are inside of your heart. When those muscles are particularly strong, you have a powerful base from which you can build up any of the other muscle groups in your body. Of course, if those muscles are weak, you are going to have a terribly hard time with making anything else stronger, simply because you will lack the necessary endurance to go through a proper workout.