When the rotor is stationary, the only resistance to current
flow is the impedance of the electromagnetic coils.
The impedance is comprised of the parasitic resistance
of the copper in the windings, and the parasitic inductance
of the windings themselves. The resistance and
inductance are very small by design, so start-up currents
would be very large, if not limited.
When the motor is spinning, the permanent magnet
rotor moving past the stator coils induces an electrical
potential in the coils called Back Electromotive Force,
or BEMF. BEMF is directly proportional to the motor
speed and is determined from the motor voltage constant
KV.