The fourth factor in metabolism is non-exercise activity thermogenesis (NEAT), which is largely based on genetic variables. It's defined as the generation or production of heat, especially by physiological processes.
It's similar to resting metabolism but even more genetically dependent. Not to worry because it only generates about 5% of your total caloric expenditure.
It's important to note that many resources describe NEAT as all daily movement EXCLUDING exercise, but as you recall, I include both daily movement AND exercise under PAL (physical activity level).
It's mainly semantics, but I think it makes more sense for PAL to encompass mowing the lawn, washing the car, working all day, etc. AND exercise.
The point is that NEAT represents the little extra bit of energy output due to the primal physiological processes of life.
Make it a great day!