Calorie Burn for Bodyweight Exercise May Be Underestimated
Although metabolic equivalent of task (MET) is a pervasive factor in the fitness industry, not many people seem to know what it is. MET is the essential value used to predict how many calories you’ll burn per hour doing some activity. It’s also the basis for calorie rates shown on exercise machines or heart rate monitors. Not only that, but MET is also used to establish guidelines that doctors, health organizations, and the government use for health interventions. A study this month in the Journal of Strength and Conditioning Research has challenged both the placement of calisthenics on the MET charts and their perceived role in human health.
While you may not be familiar with MET itself, it’s pretty easy to understand. Essentially, one MET is the amount of energy you expend sitting and doing nothing physical. Two METs is twice that much energy, and so forth. Pretty simple. When making recommendations for health interventions, organizations use METs as a means of establishing how much activity people ought to do. It’s sort of like a food pyramid or recommended vitamin intakes, but for exercise instead of food. For example, a common guideline to meet minimum health requirements is to get at least thirty minutes of moderate exercise on at least five days per week. Moderate is defined as exercises between three and six METs. An alternative recommendation is twenty minutes of vigorous activity (at least six METs) for at least three days per week.
The researchers in this study worried that resistance training may be underestimated on the official MET charts, and their point is justified. Traditional methods of measuring MET involve oxygen consumption. In fact, measuring oxygen consumption is pretty much how every estimate of calorie burn you’ve seen is created. The problem arises when we look at anaerobic activities. Anaerobic exercise, by definition, derives its energy in the absence of oxygen, so measuring oxygen consumption would, theoretically, underreport the intensity of resistance training.
Until this study, no one has compared the difference between measuring oxygen during resistance exercise to measuring it after exercise. You may be wondering why you would measure it after instead of during. Measuring oxygen is an easy way to estimate calorie expenditure, and the idea is that anaerobic metabolism could cause a delaying effect. In other words, you’ll still boost your aerobic metabolism, but not until the anaerobic exercise is done. The researchers wondered if there would be a difference between estimating energy from these two methods.
The participants did three circuits of push ups, pull ups, curl ups (sit ups), and lunges. The exercises were performed for a minute each with a set cadence. Oxygen consumption was measured while they exercised, and also while they rested in between exercises. The participants rested until they returned to baseline oxygen consumption levels between each exercise.
The researchers discovered a huge difference in MET and calorie estimates. While measuring during exercise, none of the exercises were classified as vigorous (greater than six METs). However, using the estimate obtained during rest, three of the exercises (all except curl ups) were classified as vigorous. Pull ups were the highest, at eight METs. For pull ups, this amounted to nearly ten calories per minute. While the bodyweight of the participants was strangely excluded, they appear to have averaged about 170lbs.
The results of this study could mean that many anaerobic activities, especially short-term ones like bodyweight exercises, may have underestimated energy expenditures. It’s a cool study with interesting results. Let’s hope to see more on this in the future.
1. Jesse Vezina, et. al., “An Examination of the Differences Between Two Methods of Estimating Energy Expenditure in Resistance Training Activities,” Journal of Strength and Conditioning Research, DOI: 10.1519/JSC.0000000000000375
Photo courtesy of CrossFit Impulse.