It has been proven in various studies and researches that doing cardio first thing in the morning will burn off more fat when the body is in a fasted state compared to any other time in the day. However the benefit is not restricted purely to fat burning properties, morning cardio will actually energise you and make you feel better throughout the day - it will also increase your metabolism throughout the day which in turn helps to burn more fat even faster long after you've finished your workout.
Although doing your cardio first thing in the morning is a great way to burn fat it's not the only contributing factor, the length of your sessions will also determine how effectively you burn fat. There are people who perform hours of moderate paced cardio with the intention of burning fat which quite frankly is just wasted time. Why is it a waste?
Because shorter, more intense cardio session work better to increase your energy expenditure. While performing long duration, low intensity cardio works burn more calories during the exercise, you stop burning the extra calories once you end your cardio workout. Comparatively, shorter duration cardio sessions that involve very high intensity burn less calories during the duration of the workout, but these intense sessions work to elevate your metabolic rate long after you are finished, resulting in naturally high energy expenditure.
With shorter duration cardio sessions (for example, 20 to 30 minutes), you can performing these cardio training sessions with much higher intensity than you would with long duration sessions. Think about it for a moment, if you were to train at a very high intensity, you would not be able to maintain that intense pace for long periods of time. To accomplish the goal of achieving very high intensity, you may also consider using intervals during your cardio sessions. This type of cardio exercise involves alternating periods of explosive, high intensity cardio, with periods of moderate intensity.
Because you can only maintain peak intensity for very short period of time (say 30 seconds to 1 minute), you must use intervals where you are training at peak intensity for a brief time followed by moderate pace cardio, and then start over again. High intensity cardio sessions help increase your metabolism, and help you maintain an elevated metabolism for hours after you've completed your workout. There are many approaches to using interval training.
You can set your intervals to be very short and brief, lasting only 20 to 30 seconds, or you can set your intervals to be a bit longer with each interval lasting several minutes. You can always change things up by adjusting your interval times to keep things interesting.
One of the best cardiovascular exercises to burn fat is the rowing machine. I have one of these myself, and would not trade this piece of equipment for anything else. It is a total body workout that puts more demand on your body than any other cardio exercise. My cardio sessions usually last 16 to 25 minutes and occasionally over 30 minutes. I always use interval training for my cardio sessions, and I adjust the length of the intervals randomly all the time.
For example, I might do 20 seconds at 100% peak intensity, and then follow that with 30 to 60 seconds of light to moderate pace, and repeat this several times. I may also set my peak intensity interval to around 1 to 2 minutes, followed with 2 to 3 minutes of light to moderate intensity. Note though, the shorter the interval, the higher the peak intensity you will be able to maintain. So for short 20 second intervals, I will be working at 100% peak intensity, but for 1 or 2 minute intervals, I may be working at 80 to 95% of peak intensity. You simply cannot maintain the highest peak intensity for long periods of time.
To summarize, for best fat loss results to reduce tummy fat, the best time to do cardio is first thing in the morning when your glycogen stores are depleted, and performing shorter duration, high intensity cardio session will work to elevate your metabolic rate for hours after you've completed your workout. If you apply the above fat burning tips to your workouts, you will be able to achieve good fat loss results.