First, just a few quick definitions. Intensity is defined as how hard (based on Maximum Heart Rate, mHR) a person works during exercise. Moderate intensity is between 50-60% mHR, and high intensity is 75%+ of mHR. Duration is defined as work done over a set amount of time or distance.
A common mistake most people make when starting or continuing a cardio (aerobic) program is to gradually increase the duration of the exercise. For example, they will either increase the time from 30 minutes to 1hour or will increase distance from 5 to 10 miles believing they are burning more calories since they are working longer. The cardio machine makers and their labeling of “fat and cardio burning zones” substantiate part of this myth. These zones are a misnomer based loosely on the science of how the body works. When have you ever done LESS work and burned MORE fat?
In reality, the best way to burn more calories is to decrease the duration and inversely increase the intensity of the cardio workout. The harder you work, the less time has to be spent doing the work. It has been shown that high intensity exercise burns up to 9 times more fat per calorie burned during the exercise. Also, a person working at 75% of mHR is burning 14 calories per minute vs. only 7 calories per minute at 50% of mHR. So, for each minute of exercise at 75% mHR you are burning 8.4 fat calories, and at 50% you are burning 6.3 calories per minute. Also, calorie burn lasts longer and metabolism is increased more following high intensity exercise vs. lower intensity exercise.
There are many ways that one can increase their intensity for cardio exercise. First, a distance can be set and during each bout of cardio the time for that distance must be bettered. Intervals can be incorporated. Imagine sprinting. Work is done as hard as possible for a set distance, i.e. 40 meters, or for a set time, i.e. 30 seconds. The work to rest ratio must be between a 1:1 to 1:10, i.e. 30 seconds on to 30 seconds off. Finally, cardio (aerobic work) can be integrated into anaerobic resistance training such as ball slams, jump rope, jumping jacks, burpess, etc.
The numbers speak for themselves. During high intensity cardio exercise you will burn more calories, burn more calories from fat, and have increased metabolism over a 48 hour period when compared to lower intensity exercise. Ignore the myth that easier work equals larger gains. You are how you train. The lower the training stimulus, the lower the training effect, and the higher the training stimulus, the higher the training effect. It should please all of us to know that hours upon hours no longer have to be spent trudging along on the treadmill or bike. Crank up the intensity and watch those pounds melt away. Push yourself and you will be rewarded. The numbers have spoken.