There are a variety of ways to grade motor function.  From a functional standpoint, motor function greater than against gravity is useful.  Range of motion is also important, but function that does not cover the full normal range is still quite useful.

Quantitative measurement of motor function can be made using pinch and grip manometry. 

Generally, additional formal measurements are not used, but the muscles are, to the extent possible, graded individually, and function is quantified — see Grading System Page.