Calculating Activity Burn Using METS: The Old Versus New Formula

Introduction

Metabolic equivalents (METS) are a numeric representation of the level of intensity of different activities. METS can provide estimates of Activity Burn or the number of calories burned that are associated with those activities. Table 1 shows a new formula for using METS to calculate Activity Burn. Perhaps surprisingly, The Difference continues to use the old formula. But we have good reasons for doing so which include simplicity and being conservative.

Discussion

The Difference continues to use the old formula, but we have many reasons:

• Simplicity – the old formula is simpler, has fewer variables, and, hence, has fewer error terms.
• Conservative – the old formula consistently estimates fewer calories burned than the new formula.
• Mathematics – the old and new formulas differ only by a coefficient of 5%.
• Static Calibration – the new formula is calibrated for only one particular type of person.
• Outdated BMR – the new formula uses an old formula to calculate Basal Metabolic Rate (BMR).
• Improper Units – the new formula uses improper units of measurement.

Simplicity

Although technology and business decisions are often complex, simplicity is one of our company’s guiding principles. It reflects our preference for doing things in an intuitive manner whenever possible. To learn more about our perspective, please read “Simplicity in a World of Complexity”. When it comes to the formulas, the older one is simpler, has fewer variables, and, hence, has fewer error terms. In contrast, the new formula is more complex to calculate because it involves more variables, and this introduces entry points for error.

Conservative

Using the older formula is also conservative. Studies have shown that the old formula generally underestimates total calories burned due to activity. In weight management, especially weight loss, it may be more prudent to choose underestimation rather than overestimation of caloric burn when employing the formula. While our technology can help people achieve a variety of goals, we recognize that a large portion of our clients. Therefore, we prefer to underestimate rather than overestimate calories burned.

Mathematics

Delving into the mathematics behind the two formulas also supports our decision to use the older formula. As shown in Table 2, the difference between the two formulas boils down to a simple coefficient of 1.05 or 5%. In other words, the new formula estimates that calories burned are 5% higher than the estimates from the old formula. This coefficient is equal to the ratio of a baseline oxygen consumption of 3.5 ml/kg/minute, which was used originally to determine the METS values and specific oxygen consumption of 3.3 ml/kg/minute. We know 3.3 ml/kg/minute is the denominator because when we factor out 60 minutes per hour from 200, we get a quotient of 200 / 60 = 3.3.

Static Calibration

The researchers calibrated the new formula for the specific oxygen consumption of a 40-year-old male who weighs 70 kg and is 6 feet tall, instead of enabling dynamic recalibration for any person. The specific oxygen consumption of 3.3 ml/kg/minute is calculated using the Original Harris-Benedict BMR Calculation = (13.7516m/1kg + 5.0033h/1cm – 6.7550a/1 yr + 66.4730) kcal/day. This is converted to ml/kg/minute using the following translations: BMR/1440 = kcal/minute; kcal/minute/5 = Liters/minute; Liters/minute/(weight kg)x1000 = ml/kg/minute.

Interestingly, the specific oxygen consumption for a 30-year-old male, who also weighs 70 kg and is 6 feet tall, is 3.5 ml/kg/minute. If we use this value instead of 3.3 ml/kg/minute in the new formula, then the old formula would be identical to the new formula because the ratio of 3.5 / 3.5 and, hence, the coefficient is 1. In other words, the two formulas differ solely because they chose a 40-year-old male instead of a 30-year-old.

Outdated BMR

The Original Harris-Benedict equation calculates specific oxygen consumption, which some may consider an outdated BMR model. In 1918, researchers introduced the equation, revised it, and subsequently released newer and alternative equations.

Improper Units

Using the new formula also obfuscates the original purpose of METS values, which were introduced to standardize the intensities used in various physical activities, by introducing improper units of measurement.

Conclusion

If The Difference were to entertain changes, we believe that instead of simply adopting the new formula, we should employ a more recent equation for calculating specific oxygen consumption, calibrated to each of our client’s data. In other words, we should not simply recalibrate a robust, old model to reflect one type of person. Instead, we should recalibrate the old model according to all gender, weight, and height variations. This is feasible since The Difference records these measurements in our registration process. Table 3 shows our proposed formula which still uses the Original Harris-Benedict equation. However, while supporting progress and accuracy, we believe researchers need to conduct more research to ascertain the impact of adopting this proposed formula before executing such a change.

For the time being, we believe using the old formula to calculate calories from METS values is advantageous. New does not always mean better. What do you think? Please leave your comments below.

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