The elliptical trainer has gained increased popularity in the fitness industry as a non-impact exchange for treadmill running. In fact, sales have increased as more and more walkers/joggers switch over to the elliptical trainer to meet their weight loss goals. Many users cite that the exercise is easier to perform than treadmill work with greater returns in energy expenditures. This though is a misconception and a likely contributor to reduced adaptations in response to the exercise program. Research has indicated that the elliptical trainer does not actually require the body to use the amount of calories calculated by the machine.
Energy expenditure is calculated by work expressed as MET intensities. Most fitness professionals recognize that a MET is the oxygen equivalent of 3.5 milliliters of oxygen used for each kilogram of body weight for the duration of time the action was performed (3.5 ml• kg-1• min-1). For each activity a MET value can be assigned which reflects the oxygen needed to accomplish the task. Since the body burns between 4.7 (fat) and 5.0 (CHO) calories per liter of oxygen used, identifying the oxygen needed for the work also identifies the approximate energy burned by the body for the duration the work is performed. The stationary aerobic machines used in commercial fitness facilities assign a MET intensity for each level or program in the machine’s computer, which is then used to predict total oxygen used and subsequent calories burned. The machines commonly ask for a body weight to finalize the math equation because the body’s size is needed to determine the work performed in weight bearing activities. Therefore, to be accurate, the actual work performed by the body in terms of oxygen used, must be consistent with the MET value used in the machine’s calculation of energy expenditure.
In one study published in Research Quarterly for Exercise and Sport, researchers measured the effects of different work factors such as stride rate, resistance, and combined arm/leg use on the elliptical trainer to determine the accuracy of the manufacturer’s energy expenditure predictions. The researchers tested twenty-six men and women between the ages of 21 and 40 on different training protocols using the elliptical equipment. Twenty-two participants performed two different tests, one without the arm poles using the leg-only option; the other test was performed using arm poles to identify the affects of combined work. The other four participants performed one test without the arm poles. The different tests were conducted using six 5-minute stages at two different stride rates, 110 and 134 strides • min-1, and three different resistance settings (level 2, 5, and 8). During the tests researchers assessed steady-state oxygen uptake (VO2), minute ventilation (VE), heart rate (HR) and rating of perceived exertion (RPE) for each participant.
As one would expect, when participants increased stride rate and resistance all measures increased. Ventilation and heart rate increased most notably between Levels 5 to 8, consistent with lactate accumulation. Researchers found that in all cases the manufacturer's calculated energy expenditure was overestimated. Additionally, the values varied significantly, which researchers attributed to experience and technique. As with any action, inefficient movement increase caloric demands and compensatory actions reduce the demands such as body weight supported postures. The researchers found that the elliptical trainer can be used to increase VO2 when the heart rates and RPE are consistent with 60-80% of VO2 reserve and heart rate reserve. But, due to the wide variability in VO2, and calculations used, predicting the metabolic cost during elliptical trainer exercise for an individual is not appropriate.
It has been surmised that the calculations used are based on running and stepping which would likely explain the predictive error. Running uses a lift phase and a landing phase, which requires greater acceleration and deceleration forces while stepping requires both a lift phase and deceleration phase. Both activities, particularly due to the lift phase, provide more work than actually performed by the non-impact trainer for the same distance moved (work = force x distance). In another study, leg-only exercise was compared to combined arm and leg exercise on the elliptical trainer. Although both of the techniques were again found to over predict the caloric costs of the activity when measured using spirometry, the combined arm and leg action was closer in prediction. These findings suggest that machines with arm attachments require arm action in the calculation and subsequent prediction.
Individuals using the elliptical trainer for caloric expenditure are better served using the upper and lower body attachments of the machine because, as one would expect the more perceived work being done the more calories actually being burned. The elliptical trainer certainly can adjunct any conditioning program but when used for caloric expenditure it is important that the over prediction be accounted for to improve accuracy in the energy balance equation.