# FAQ

### 1. What is a METy?

In adults, 1 MET represents an oxygen uptake of 3.5 mL·kg-1·min-1 or 1 kcal·kg-1·hr-1. Due to metabolic differences in children and adolescents, adult MET values are not applicable to children. Youth have higher basal metabolic rates per unit body mass than adults, and typically expend more energy per kilogram of body mass for physical activities than adults. In this new Youth Compendium, physical activity energy expenditures are reported in multiples of metabolic equivalents or youth METs (METy). One METy represents the basal metabolic rate. For this compendium, BMR was calculated using the Schofield equations accounting for sex, age-group and body mass of the child. Additionally, the METy values for specific activities are presented for four age groupings. METy values for each physical activity were derived from literature reviews, data analysis, and imputation.

### 2. How should information from the Youth Compendium be used?

Youth Compendium information should be used to convert time spent in different activities to units of MET scores. Values are best used to represent group-level estimates for energy expenditure. In cases where individual estimation is desired, users should realize that energy expenditure can be influenced by many factors not represented by values in the table (e.g., body size, economy of movement). Thus, users should understand that these values are truly estimates and are not recommended to be used for precise estimates of individual energy expenditure. Youth Compendium data can also be used to help determine the intensity level (e.g., moderate- or vigorous-intensity) of a specific activity for a specific age group.

### 3. What is the difference between the smoothed and observed/imputed METy values?

Both the smoothed and observed/imputed METy values come from the same data sources. The observed/imputed METy values represent the mean value for each activity and age group. The smoothed value is calculated from a linear regression model where METy is regressed onto age. Smoothing the estimates served to remove some of the natural variability across age groups in the observed METy values within each activity.

### 4. What do the activity codes mean?

Codes have 6 digits. The first two digits represent an activity category, the next three digits represent a specific activity, and the final digit represents age group. It is important to note that in the web version, age group is represented by an “x” in the activity code, because the 4 age group values are listed across one row in separate columns.  However, in the downloadable file, age group is included in each code for each METy value.
Here is example code for walking at 3 mph for a 13-15 year-old:

CodeActivity CategorySpecific ActivityAge Group
80200480 (Walking)200 (Walking 3.0 mph)4 (13-15 years)

### 5. How do I calculate energy expenditure from METy values?

Total energy cost of a physical activity can be estimated based on the METy from the Youth Compendium, a measured or computed BMR, and duration of the specific activity, as follows:

Total energy cost (kcal) = METy x BMR (kcal/min) x duration (min)

where BMR for boys is measured or predicted from Schofield equations:

3–10y BMR (kcal/min) = [22.706 × Weight (kg) + 504.3]/1440

10–18y BMR (kcal/min) = [17.686 × Weight (kg) + 658.2]/1440

and where BMR for girls is measured or predicted from Schofield equations:

3-10y BMR (kcal/min) = [20.315 × Weight (kg) + 485.9]/1440

10-18y BMR (kcal/min) = [13.384 × Weight (kg) + 692.6]/1440

Example:  What is the energy expenditure for a 14-yr-old girl (who weighs 40 kg) walking at 3 mph for 20 minutes?

Total energy cost = METy x BMR (kcal/min) x duration (min)

4.3 x BMR x 20 where BMR = [13.384 × 40 kg + 692.6]/1440

4.3 x .853 x 20 = 73.3 kcal

### 6. How do I search the Youth Compendium?

To view the tables, click either METy values. Next you will need to click on either “View All Categories” or click on an individual category within or “View by Individual Category”. Now, in the upper right-hand corner of the table, start typing your keyword inside the search box. The table will automatically filter for matching results.