Energy expenditure is most often reflected in the number of calories that we burn during exercise. A calorie is the amount of heat required to raise 1 gram of water 1 degree Centigrade. Therefore, the total caloric expenditure during exercise is really a measure of the amount of heat given off by the body during the activity. Measuring this directly is very complicated and impractical, involving a sealed air chamber and water bath. There are, however, indirect measures of caloric output.
The best indirect measure of caloric expenditure is the volume of oxygen consumed during exercise. There is a very linear relationship between oxygen consumption and calories expended. In fact, the body utilizes, on average, approximately 4.8 calories for each liter of oxygen that it consumes.
We could apply a standard measure of oxygen consumption to different forms of exercise, such as running at 5.5 miles per hour, multiply that by the duration of the exercise bout, and then again by 4.8, yielding total calories consumed during that exercise interval. This is, in fact, the way many devices compute caloric expenditure. The problem with this method is that there are many factors, such as body weight or fitness level, which may alter the volume of oxygen consumed during exercise. It is necessary, therefore, to actually measure the volume of oxygen consumed during exercise, using metabolic analysis equipment. This too is both complex and impractical outside of a medical or university laboratory.
A second level of indirect calorimetry involves the use of heart rate. In most people there is a direct relationship between heart rate and the amount of oxygen consumed. In fact, many prediction equations which calculate oxygen consumption from heart rate have been established. Thus, by applying the associative property we can see that if oxygen consumption equates to caloric expenditure, and heart rate equates to oxygen consumption, then heart rate equates to caloric expenditure. This, in fact, is the principle upon which heart rate monitors can calculate calorie burn. There is, of course, one caveat.
According to Astrand and Rodahl, when using heart rate to compare caloric expenditure on two different devices, it is necessary to ensure that both devices utilize the same large muscle groups, since cardiac output will be influenced by the number and size of working muscles, and the relative level of work performed by those muscles. Thus, if two devices having similar movements, involve different muscles, and those muscles are working at different percentages of their maximum capacity, then the caloric expenditure from those devices cannot be predicted from the heart rates achieved during exercise. This explains the difference, in caloric expenditure, between the Cybex Arc Trainer and other elliptical products.
An independent study, conducted by Florida Atlantic University , revealed that the Cybex Arc trainer is biomechanically more efficient than the leading elliptical trainer, and in fact, is better at activating the large muscles of the lower body. Where the Arc Trainer was effective at involving the knee and hip muscles, the elliptical’s movement pattern concentrated the muscular effort at the knee, and could not effectively engage the large muscles of the hip. This difference in muscular activation has a significant effect on the metabolic demands of the two devices.
In a second study, conducted by the University of North Carolina at Charlotte, it was demonstrated that the level of perceived exertion and the heart rate response of subjects exercising on the Arc Trainer significantly lower than those of subjects exercising at the same percentage of energy expenditure on a leading elliptical trainer. The difference in perceived effort and heart rate response is directly related to the biomechanical efficiency of the Arc Trainer.
In order to bring heart rate on the Arc Trainer up to the same level as the elliptical, therefore, subjects would have to increase their workload and oxygen consumption, thereby exercising at a higher level of caloric expenditure. Since most people adjust the workout intensity of cardio devices to their perception of effort or heart rate response, then it is most likely that they will be working at a higher intensity, and thus consume more oxygen and burn more calories on the Arc Trainer than they would on elliptical trainers, and could very well achieve this in a shorter period of time.
Paul M. Juris, Ed.D.
Executive Director CYBEX Institute for Exercise Science
Dr. Juris earned his Doctorate in Motor Learning from Columbia University in 1993, followed by a variety of positions in higher education, rehabilitative medicine, professional sports, and fitness. Paul Juris, Ed.D. was named Executive Director of the CYBEX Institute for Exercise Science in January of 2007
Cybex is a provider and manufacturer of premium commercial fitness equipment. Content featured in the Cybex Fitness Blog is meant to inspire healthy living and wellness and should not be taken as medical advice. For medical advice please consult a doctor.