Cross training is effective for weight loss because when you cross train, your body will never get a chance to get used to any type of exercise. The definition of cross training depends on whom you ask. The website medicinenet.com defines it as, "Doing two or more aerobic activities such as jogging, bicycling and swimming on a regular basis." According to one of many definitions on the website mimi.hu, "Cross-training is a type of exercise regimen that combines strength work, aerobic work and stretching."
Pick at least three activities that your body is not used to. So, if you normally run, this would be something that you would not do because your body is already used to running. When your body is used to a certain form of exercising, it means it will burn fewer calories doing the specific activity. Instead, pick spinning, circuit weight training and swimming. Do spinning one day for 45 minutes to an hour and circuit weight train the next day for the same amount of time, and then swim the third day. On the fourth day, take it from the top, meaning you will spin again, followed by circuit weight training the fifth day and swimming the sixth. Take a break the seventh day, and do nothing at all. You need to give you body a break once in a while or else you run the risk of overtraining.
After a month, replace one of the cardio days with another type of cardio. In other words, now that you have not been running for a while, your body is no longer used to this type of exercise, meaning that you are now free to integrate it into your cross training routine. The following month, you can cut out the swimming and go back to spinning again. It also a good idea to switch up the order of the exercises you do in your circuit weight-training routine.
In addition to keeping your body guessing, by cross training you avoid getting overuse injuries since you do not overdo any one activity.
Keep in mind that the absolute fastest way to lose weight doing cross training is to apply the same rule as you do to any of exercise--the harder you work out, the more results you will get, no matter what you are doing. However, if you are new to exercising it is not wise to go all out in the beginning. Start slowly, listen to your body, and do not work out on consecutive days until you feel you are ready for it.