How Accurate Are Calorie Counts on Cardio Machines?

You may not be burning as many calories as the treadmill says

People exercising in health club

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Calorie counters on treadmills, ellipticals, and other cardio machines are convenient. At the end of your work, the number of calories you burned can be surprising. It can certainly make you feel better and keep you motivated to run or exercise more.

Before you completely write off that high-calorie lunch you enjoyed, it's important to know that these are just rough estimates. While some types of cardio machines are more accurate than others, none of them will be 100 percent accurate. In general, they overestimate your calorie burn by 15 to 20 percent because there are too many factors involved.

Calorie Burn Factors

Many of the hi-tech cardio machines found in gyms today ask you to enter your personal details before you begin. This often includes your weight and some also factor your gender and age into the equation. The problem is that there are other important factors to consider.

Cardio machines such as treadmills use standard formulas to figure out the number of calories burned. It is similar to a calorie-burn formula that you can do on your own. In either of these, factors like your fitness level and your body composition and size are not accounted for.

  • Fitness Level: Whether you're just starting a general exercise program or switching activities, the newer you are to it, the more calories you will burn. As you become more efficient and fit, you will burn fewer calories doing the same activity for the same period of time.
  • Body Composition: When you start exercising, it's likely that you will have more fat than muscle mass, so you will burn fewer calories at first. As you build muscle, your body becomes more efficient and will burn more calories for the same amount of exercise.
  • Body Size: Between two people who weigh the same, someone with a larger frame can burn more calories.
  • Age: Some machines factor in your age and others don't. Nonetheless, as you grow older, you will not burn the same number of calories as you did when you were younger. You can make up for this by extending your workout times or the intensity of your routine.

For example, if a 160-pound woman with 35 percent body fat and a 160-pound woman with 20 percent body fat are both running at a 10-minute mile pace, the treadmill will display the same amount of calories burned. However, the woman with the lower body fat and more muscle mass is actually burning more calories.

Experience and Efficiency

More than with other machines, when you run on a treadmill, your form and efficiency play a larger role in calorie burn. The machine cannot account for these factors. New runners will usually burn more calories than more experienced runners running at the same pace and distance.

The reason is that a beginner tends to be inefficient with a side-to-side movement and lots of bouncing up and down. These extra motions expend more energy than the experienced runner's efficient stride. This will change over time as you perfect your stride, but it's an important consideration.

Also, if you are using the handrail on a treadmill or stair stepper, you may be diminishing your calorie burn because you're making the workout easier. You won't be swinging your arms naturally with your stride.

Due to the way athletes use them, there are also variables in the accuracy of different types of machines. For example, a stationary bike limits movement so everyone uses it in generally the same way. The calorie counters on these are much more accurate than treadmills and stair steppers, which offer more freedom of movement. 

Cardio Machine Formulas

The formulas that cardio machines use to calculate can vary from one manufacturer to another. Generally, most machines will base their formula on The Compendium of Physical Activities. Initially developed in 1987 and receiving regular updates, it assigns a value to a variety of activities, from exercise to inactivity, and sex to home repairs. The values are based on the Metabolic Equivalent, known as MET.

One MET unit is equal to 1 kcal (kilogram calorie) per kilogram per hour, essentially the amount of energy expended when "quietly sitting." The amount of energy (calories) you burn for other activities is compared with this baseline.

Once again, there are many factors involved and the Compendium gives many options. For instance, the running category is filled with variables. It states that jogging burns 7.0 MET (7.0 kcal/kg/hour), running 6 miles per hour (a 10-minute mile) burns 9.8 MET, and running 10 miles per hour (a 6-minute mile) burns 14.5 MET. This does not account for anything to do with you personally.

Wearable Fitness Trackers

If you can't rely on the cardio machine's calorie counter, can you turn to your personal fitness tracker? These popular wearable devices can monitor all sorts of your things related to your health and activity level, so they're a great option for tracking your workouts.

A study at Stanford University took a look at seven different devices to check their accuracy. The results showed that the most accurate of them was off by an average of 27 percent and the least accurate by 93 percent. The heart rate monitor was the most reliable function, but the researchers concluded that the calorie counter should not be counted on.

Reliable Alternatives

Whether it's a cardio machine or your fitness tracker, it's best to take the calories burned readings with a grain of salt. It's fine to use the numbers as a benchmark for your workouts, but don't plan on consuming additional calories based on that number. That's an easy way to start gaining weight, despite your best exercise efforts.

For example, if the treadmill says that you burned 300 calories, take at least 20 percent off that total and estimate that you burned about 240 calories.

You can also gauge your workout by your perceived exertion or track your target heart rate. This can also help you when moving from one machine to another. If you get the same reading on two machines for the same duration but one seems easier, you're probably burning fewer calories on that one.

A Word From Verywell

Having a general idea of how many calories you're burning during exercise is a good way to manage your health and weight. Just keep in mind that any of the calorie counters are probably overestimating what you're actually burning. These are just numbers, though, and how you feel after the workout is more important.

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Article Sources
  • Healthy Lifestyles Research Center. Compendium of Physical Activities. Arizona State University. 2011.
  • Shcherbina A, et al. Accuracy in Wrist-Worn, Sensor-Based Measurements of Heart Rate and Energy Expenditure in a Diverse Cohort. Journal of Personalized Medicine. 2017;7(2):3.