Well, how’s this for answer: any kind. That’s right, anything that is high intensity over a short period of time will do. You could do some weight training or maybe sprinting while you take your daily jog or swim laps. Don’t let the idea of weight training scare you. You don’t need to go to the gym or buy expensive equipment if you want to try weight training. You can do a complete weight training circuit with only a couple of dumbbells right in your own home.
Circuits are especially effective to burning fat because they combine aspects of both strength and endurance training into one, highly targeted, set of exercises. This type of training is highly effective in making your muscles stronger and more fit, meaning you’ll be less susceptible to injury over the long run. Circuit training is generally not used when trying to build muscle mass, but remember you’re not necessarily trying to build a ton of muscle, just lose fat.
Always remember to give yourself a day of rest in between whatever anaerobic exercises you decide to do. It’s very important that you give your muscles time to rest, not doing so can result in injury. Also be sure that you sufficiently stretch before any kind of exercise. For some reason this is something that many people neglect, even though anyone who’s ever been in a PE class knows how important this is for avoiding injuries.