They say that variety is the spice of life. Many people who exercise incorporate cross-training over the course of their weekly workout. Simply put, cross-training means doing different activities on different days. For example, someone working out 5 days a week might choose to do brisk walking on 2 of those days, biking on 1 day, and the elliptical machine on the other 2 days. Cross-training enthusiasts typically cite ‘reduced boredom’ as one of the reasons for choosing this mode of training. Next, let’s discuss physical activity guidelines and some ways to track activity.
The current Public Health Guidelines for Physical Activity recommend that adults accumulate a minimum of 150 minutes each week of moderate intensity activity, or a minimum of 75 minutes each week of vigorous intensity activity, as well as 2 days each week of resistance training. These numbers reflect the amount of physical activity necessary to achieve significant health benefits. If a high level of fitness or significant weight loss is the goal, then the number of minutes listed should be doubled. For individuals who like to track their activity in more detail than by simply using the number of minutes, the concept of MET-minutes may be helpful. This is especially true for individuals who do different activities at different levels of intensity over the course of the week. In this context, a MET is not a National League baseball player. Rather, a MET is a unit of energy expenditure (you can think of energy expenditure the same way as calories burned). Resting energy expenditure is defined as 1 MET. So, if I was exercising at 5 METS, it means that I am expending 5 times the amount of energy than I would at rest. If I exercised for 40 minutes at 5 METS, then I would accumulate 5 x 40 = 200 MET-minutes during that session.
Using this information as a background, let’s consider the person at the beginning of the blog as an example:
- Walk 2 days a week at 5 METS for 30 minutes per session = 2 x 5 x 30 = 300 MET-minutes
- Bike 1 day a week at 7 METS for 20 minutes = 1 x 7 x 20 = 140 MET-minutes
- Elliptical machine 2 days a week at 6 METS for 40 minutes = 2 x 6 x 40 = 480 MET-minutes
- Total MET-minutes for the week = 300 + 140 + 480 = 920 MET-minutes
At this point you are probably wondering about a few things:
1) How many MET-minutes per week are recommended?
2) How do I know my MET level when I am working out?
3) How do METs translate into calories burned?
The answers to these questions can be found below:
1) The Physical Activity Guidelines mentioned earlier include a recommendation of 500-1,000 MET-minutes per week for significant health benefits. You will likely need more than this if significant weight loss is your primary goal.
2) The easiest way for you to determine your MET level during physical activity is to use the Compendium of Physical Activities. The Compendium shows MET levels for hundreds of different types of physical activity (including household and occupational chores) at different levels of intensity. Here are a couple of examples:
For running 6 mph (10 minutes per mile), the Compendium shows a value of 10 METS. If someone ran for 30 minutes at this pace, then they would earn 10 x 30 = 300 MET-minutes.
For biking on a level surface at 12.5 mph, the Compendium shows a value of 8 METS. If someone biked for 45 minutes at this pace, then they would earn 8 x 45 = 360 MET-minutes.
3) Once you know your MET value, multiply this number by 3.5, and then multiply by your body weight in kilograms (divide your body weight in pounds by 2.2 to determine your weight in kilograms). Take the result and divide by 200 in order to determine your calories burned per minute. Here is an example using someone who is working at an intensity of 10 METS and weighs 180 lbs (82 kilograms):
10 METS x 3.5 x 82 / 200 = 14.4 Calories per minute. If they ran at this pace for 30 minutes, then they would burn approximately 14.4 x 30 = 432 calories. For significant health benefits, the Guidelines recommend burning 1000-2000 calories per week through physical activity. You would need to set your long-term calorie expenditure goal higher than this if significant weight loss is your primary objective.
It’s important to remember that you don’t necessarily need to go to the gym each time that you want to be physical active. Occupational and household chores count towards your weekly MET-minute goal. The Compendium tells us that vacuuming and pushing a power lawn mower have energy expenditures of 3.5 and 5.5 METS, respectively. So, if you did each of these tasks for 30 minutes on a single day, you would earn (3.5 x 30) + (5.5 x 30) = 270 MET-minutes for the day.
Of course, if all of this math bores you to death, then you can use a wearable device to estimate your caloric expenditure. The Compendium is free though!
Ainsworth, B., Haskell, W., Hermann, S., Meckes, N., Bassett D., Tudor-Locke, C….Leon, A. (2011). 2011 compendium of physical activities: a second update of codes and MET values. Med Sci Sports Exerc, 43(8):1575-1581. doi: 10. 1249/MSS.0b013e31821ece12.