Calorie Count uses the information listed in The Compendium of Physical Activities to find the calories burned in physical activities. The Compendium was developed to standardize the assignment of MET intensities to physical activity for use in research.  A MET is a standard unit used to estimate the amount of oxygen used by the body while performing an activity.  Activities with a high MET level make the body work harder and consume more oxygen.  The MET method is very reliable for calculating calories burned in specific activities; however, the values do not account for differences in calorie burning based on age, sex, muscle mass, efficiency of movement, and environmental conditions.  Individual differences in energy expenditure for the same activity can be large, and the true energy cost for an individual activity may not be the same as the MET value.