In reaction to last week’s column on whether the calories burned while using cardiovascular machines like treadmills and steppers are accurate, a reader wanted to know how many calories are burned while doing aerobic classes. This is an important question since many women (and some men) do aerobics as a way of controlling their weight. Most of us don’t have the time to spend hours in the gym so it is to our benefit that we make our aerobic classes as time- and calorie-efficient as possible to get more value out of them.
Exactly how many calories you actually burn doing aerobics depends on how much you weigh, the speed of the music, the quality of your movement and the kind of movement. Let’s take a look at how these factors affect the three most common types of aerobics classes --step, high-low impact, and kickboxing.
How much you weigh.
It takes more energy to move a heavier mass than it does to move a lighter one. That is one of the laws of physics. That’s why a lighter and smaller car consumes less gas than a heavier and bigger car. So whenever you look at a chart that lists how many calories are burned for a particular activity, take note of the weight of the "reference" person the calculations are based on. Then you can more accurately estimate how much you would burn. For example, a 150-pound person would burn approximately 170 calories for thirty minutes of low impact aerobics while a 130-pound individual would burn 148 calories.
The speed of the music.
Generally, the faster you move, the more calories you burn. This would seem to suggest that if you want to make the most out of your aerobic class time, you should be using really fast music. However, there are other things to consider like the long-term safety of your joints. Unfortunately, at faster speeds people tend to fling their arms and legs and this can cause joint damage over a period of time. In terms of the risk-benefit ratio (how much benefit you get for the risk you take), this is not a good deal. Your joints are much more important than burning more calories per class.
The quality of your movement.
When I was learning how to become an aerobics instructor, one of the things my trainer kept drumming into my head was to exaggerate my movements. What she meant was that I had to emphasize my body movements with full range-of-motion and power so that I could motivate my students. I remember thinking, "Wow, this is hard work" because by emphasizing my movements, I was taking the intensity of my workout to a much higher level than I ever experienced as a student.
It is a common story among aerobic instructors that their students complain that the class is not "hard" enough and yet the teacher is practically killing himself or herself with the intensity. The problem lies in the fact that the students are usually doing "baby" movements. The quality of their movements is mediocre. Even a kickboxing class can be so-so in intensity if the students will only use their arms to box instead of getting the power of the moves from their whole body.
Since it’s introduction in the late Eighties, step aerobics has become a staple in gyms around the world. The popularity of step lies partly in the fact that the intensity of the class remains fairly unchanged from the beginning to the end of the class. As they say, "You can’t fool the bench". Even if you are tired, you still have to go up and down carrying your full body weight. In other forms of aerobics, you burn fewer calories as you get tired because you subconsciously make smaller movements. However, in spite of this built in advantage of step aerobics, there are still ways to increase the amount of calories you burn per session.
The caloric cost of step aerobics is anywhere from six to 11 calories per minute. It all depends on how much you weigh, how high the bench is, whether you are using your arms or not, whether you are stepping on or hopping on the bench, and how fast the music is.
The higher the bench, the greater the calorie cost. According to researchers, doing step aerobics on six-, eight-, ten- and twelve-inch benches respectively consumes about 7.5 calories, 8.5 calories, 9.5 calories and 10.5 calories per minute. In general, for every two-inch increase in step height, there is a corresponding 17 percent increase in calorie burn. However, this is not always safe way to burn more calories because if you use a bench height that is too high for you, you will eventually destroy your knees. How do you know if the bench height is appropriate for you? The right height is dependent on the length of your thighbone and your cardiovascular fitness level. If your knees advance past your toes as you step up, your bench is too high for you. Unless you are over 5’4", a six inch bench is usually the most comfortable for your knees. Most beginners should start with a four-inch bench regardless of their height.
Using arm movements increases caloric cost as if you had switched to a bench that was two inches higher. "Power" moves like hopping, leaping, and propelling on the bench does the same.
Therefore, you could be on a four-inch bench, using your arms to the fullest while hopping on the bench and you would be burning as many calories as a person on an eight-inch bench who was not using her arms and was not hopping.
You might think that adding hand weights would be a good way to drive your caloric count higher. Here’s what research has found. There is not much difference between using one-pound hand weights and arm movements with no hand weights at all even though the hand weights might make you feel like you are working harder. Using two-pound weights will increase caloric burn by about 1 calorie per minute (the same as a two-inch increase in bench height). However, the weights have to be pumped vigorously and this will eventually cause problems in the shoulder joint aside from the fact that the shoulder muscles get fatigued rapidly. Using three-pound weights actually resulted in fewer calories because the participants couldn’t keep up with the speed of the music and they slowed down their arm movements.
Aerobic kickboxing is a relative newcomer to the scene but it has many avid followers who love the intensity they feel they are getting from it. In 1999, the American Council on Exercise wanted to find out exactly how many calories are actually burned doing aerobic kickboxing. They commissioned Dr. Len Kravitz of the University of Mississippi to do a study using trained participants and a trained instructor. They used a music speed of 138 to 145 beats per minute (a common speed used in this type of class). They found that the calorie burn is anywhere from 6.45 to 8.3 calories per minute. A combination of punches and kicks burned the most number of calories (8.3) compared to kicking only (7.5 calories) and punches only (6.45 calories).
High-low impact aerobics.
Low impact movements always have one foot on the ground while high impact movements include jumping or hopping so that both feet are off the ground momentarily. Generally, low impact aerobics will burn about 5.7 calories per minute while high impact aerobics will burn about eight calories per minute (based on a 150-pound individual). It would seem that high impact aerobics would be more effective at burning calories in the same amount of time. Unfortunately, many people cannot do high impact aerobics because of the amount of force that their feet and lower legs have to endure. It is possible to do low-impact aerobics and get high-impact calorie burning if you know how to do it right. The key is to emphasize your movements by taking bigger steps, covering more space during movements that take you forwards and backwards or side to side, coming up and down more during moves that require you to bend your knees, lifting your legs higher, and using more powerful arm movements.
Intense but safe.
Safety is always the number one issue to consider because your body doesn’t have spare parts available. However, you also don’t want to waste time when you could be burning more calories. So the trick then is to walk a tightrope wherein you challenge yourself but you still stay within the safe range. Protect your joints but don’t baby yourself either when you could actually be doing more.