Sample specs of a treadmill motor.
Model taken into account is ZYT 93-73
Characteristic curve shows volts, amps, rpm of the treadmill motor
As you can see (it's a general rule) the efficiency for the treadmill dc motor is max with top speed and voltage (i.e. when running) and very low when walking.
So if you need to walk long time on your treadmill, it's suggested to install a low friction walking belt (you can find it on partsfortreadmill.com), lube regularly the deck surface, and keep an eye on motor temperature, to avoid motor overheating (on the same partsfortreadmill.com you will find a convenient thermometer to be installed on the motor metal casing, with a long lead, so you can check temperature easily and you don't need to open every time the motor cover.