functional strength resides in the thumb and index finger.
Can you imagine this guy walking up to a car to try and fix a flat tire to demonstrate his functional strength.
Strong guy: I fix flat tire.
Person: Thank you
Strong guy: I pick up car and carry it like big log.
Person: Um, please do not do that sir. Just fix my flat tire.
Strong guy: Me, no how. Just move big log.
Person: Are you saying you don't have functional strength, sir?
Strong guy: No, functional strength. Just move big log, have dumb brain
Person: Okay, sir, step away, I will figure it out.