One clue might be that of course seeing as your sensory neurons are not going to be completely saturated or suppressed in temporary parasthesia -- and certainly not all of them in an area will be -- and the same goes for any motor neurons that you might snag in a similar manner. The difference is that the translation from motor neuron stimulation to motor movement involves integrating a lot more components that might mitigate the effect that pinching a couple disparate nerve endings would have.

Taking from Knudson's Biomechanics (ch. 4 pp. 95--96):

>If the muscle fibers of a motor unit twitch in unison, how does a whole muscle generate a smooth increase in tension? The precise regulation of muscle tension results from two processes: recruitment of different motor units and their firing rate.

>Recruitment is the activation of different motor units within a muscle. ... Firing rate or rate coding is the repeated stimulation of a particular motor unit over time. ...

>When muscle is artificially stimulated for research or training purposes to elicit maximal force, the frequency used is usually higher than 60 Hz to make sure that motor unit twitches fuse into a tetanus. A tetanus is the summation of individual twitches into a smooth increase in muscle tension.

>... at the whole muscle level[,] muscles are activated to in complex synergies to achieve movement or stabilization tasks. Muscles are activated in short bursts that coordinate with other forces (external and segmental interactions) to create human movement.

And there's a bunch of more details to recruitment and firing rate, and it goes on in complexity and unknowns pursuant to further research. One relevant point is that in many cases you use only one firing per motor neuron, over several different neurons, to create a long smooth complex movement (the example they use is bicycling). Since it's an integrating effect, a single missing signal may not actually cause much of a problem -- but I don't know. Anyway, it's a clue.