Normally you do sprint intervals on a moving treadmill by alternating between rest and running at its fastest setting, but try this advanced twist: leave any treadmill off, and use your own two legs to power the belt for an incredible sprint workout.
As someone who has worked for fitness equipment manufacturers, please don’t do this and if you do this in a commercial gym, you ought to be kicked out.
First of all there three types of treadmill motors: A/C, brushless DC motors, and traditional DC motors. For sure you will cause damage to traditional DC motors doing this. On brushless DC motors, you might not be damaging the motor directly, but any resistance you feel is current that you are generating that is going somewhere. It’s either going into the circuitry and damaging it, or it is overheating some safety resistor. It’s also possible that the head roller or drive pulley is not moving at all and what you feel is actually the drive belt or the running belt slipping on the roller. This will damage a $450+ belt (on commercial machines) that is designed to slide against a phenolic surface, not a metal roller . On AC motors, this is pointless since any resistance you feel is between the belt and the deck and belt. If the belt is working correctly, there should be almost no resistance on an AC treadmill. Stick with bikes and ellipticals for this kind of workout, they use alternators which are designed to generate current and have circuitry to dissipate it appropriately.
TLDR: Doing this could be damaging to electronically powered treadmills. If you choose to do this, please proceed at your own risk.