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Any kind of cardio activity will help here. But if you do something that will focus more on the areas you want to loose, it can possibly help to speed up the rate of fat loss/toning (although this is not the case with everyone).

So because you are looking for your chest and stomach, I would suggest something that really focuses on your core muscles. Something like boxing would be good for that. A lot of the focus is on developing your torso and arm muscles.

To speed up the process by increasing your metabolism, you should also include some weight bearing sessions as well. Whether it's body weight bearing or using weights, it doesn't matter. By increasing your muscle mass by just .45kg (1lb), you will burn an extra 50cal (210kJ) per day.

With the weights, either do a complete session, or break it up into muscle groups over the week. Like you could do a complete session where you work on all major muscle groups, or break it up by doing one session for your hamstrings and your abs, he next session for your quads and your chest etc.

If you are just starting to exercise, aim to have at least 2 sessions of cardio (20min) and 1 or 2 sessions of weight training per week.

If you are fit enough, try for at least 3 sessions of cardio (30min) and 2-3 sessions of weight training.

With the cardio, try to mix it up. Maybe alternate weeks of running and cycling, or alternate sessions.

Another technique that you could try instead of cardio, is interval training. For example, if it is cycling - cycle easy to moderate for 4 min, cycle at max for 1 min. If that is too hard, try for 3 min moderate and 30sec at max effort. This can be done with any activity: swimming, running, skipping, skiing etc. Start off with 15 to 20 min and work up to at least 30min.