Physical Activity Level (PAL)
Physical Activity Level (PAL) is a way to express a person's daily physical activity as a single number.
What is Physical Activity Level (PAL) ?
Definition of Physical Activity Level:
A person's Physical Activity Level (PAL) is defined as that person's total energy use over a 24 hour period divided by his or her basal metabolic rate.
- It is convenient to consider both physical activity and metabolic rates over a specified period of 24 hours because activities including waking and sleeping tend to be repeated in 24 hour cycles. Therefore some definitions of Physical Activity Level specify:
"total energy required / used over 24 hours divided by basal metabolic rate over [the same] 24 hours".
- This definition of PAL applies for non-pregnant, non-lactating adults. Pregnant and breast-feeding women require comparatively more overall energy than other adults per 24 hours.
Equations for Physical Activity Level (PAL):
Simple equation for PAL:
The above applies over a 24 hour period but does not state this in the equation itself.
A more complete statement is:
Why is Physical Activity Level a useful quantity ?
A person's physical activity level - combined with his or her basal metabolic rate - can be used to calculate the amount of food energy that person needs to ingest in order to maintain maintain his or her health without gaining excess weight (see more about the energy-balance re. food intake vs energy used by the body). That is, for non-pregnant and non-lactating adults:
Food energy requirement (per 24 hours) = Physical Activity Level x Basal Metabolic Rate
Isn't there another version of this equation ?
Yes. Some courses use the above definition. Others also include discussion of dietary reference values (DRVs), one of which is 'Estimated Average Requirement (EAR)'. In general, dietary reference values indicate the quantity, or "amount", of intake of a specific nutrient or type of nutrient that will satisfy a particular proportion of the population. EAR is the amount of energy needed to satisfy 50% of the population. Students whose courses include DRVs may therefore be familiar with the equation:
EAR = PAL x BMR
which is very similar to the equation above.
The difference between these two equations is:
For exact values for a specific individual person:
Food energy requirement (per 24 hours)
When using average values to estimate DRVs for a population in general:
EAR = PAL x BMR
How is Physical Activity Level calculated ?
Physical activity level can be estimated using a list of the physical activities a person performs within a 24 hour period and the amount of time spent on each activity, e.g. walking to work, light housework, swimming, carrying bricks at work, or whatever applies to an individual person. There is a value call the physical activity ratio for each activity. The list of activities is used to find the relevant values of physical activity ratio then calculate an overall physical activity level value for the 24 hour period using time-weighted averages of the physical activity ratios.
Typical values of Physical Activity Level (PAL):
The following examples give an indication of the range of values of PAL.