This is an important factor in working out how many calories you will need to consume daily because people have different jobs with a different amounts of physical activity.
If someone has a desk job and drives to work and does no other physical activity, then his calorie content will be lower than someone who has a physically demanding job such as working on a construction site and plays football in their spare time. This is what you have to take into consideration to get the right amount of calories to build muscle.
We can work this out by looking at the chart below
Physical Activity levelsP.A.L Light Moderate Heavy
Non active 1.4 1.6 1.7
Moderately active 1.5 1.7 1.8
Very active 1.6 1.8 1.9
The P.A.L column means non occupational activity (what you do outside of work i.e football, rugby, swimming, cycling, etc...)
The Light, Moderate and Heavy columns mean occupational activity (what you do in work i.e a desk job, postman, construction site worker etc..)
In the other page Basal Metabolic Rate we worked out that in our example a 24 year old bodybuilders BMR was 1,652 calories and he has a very physical construction job and goes to the gym at least 3 times per week, so if we look at the table and look down the non occupational activity we can see that as he goes to the gym a lot he is very active, then we go along that row and look at his occupational activity and because he has a physical construction job (bricklayer) this means that it is a heavy job so his P.A.L would be 1.9.
Now we have worked out that his P.A.L is 1.9 we can do this following equation:
Esitmated calorie intake = BMR × P.A.L
1,652 × 1.9 = 3140(it was 3138 but i rounded it up)
So for a 24 year old construction worker who goes to the gym at least 3 times per work he needs to be consuming 3140 calories per day to gain weight/build muscle.