If you are experiencing your TV going black/ fuzzy / blurry / or scrambled picture when your treadmill is running, then you need to plug the TV and Treadmill into separate outlets that are on different fuses in the electrical box. There's a good chance there's interference going on with the circuit of the TV and Treadmill. Keep in mind, Treadmills don't seem to play nice with GFCI outlets. If your treadmill is tripping the circuit breaking, it could be an AFCI breaker, which treadmills also don't seem to play nice with. A Tripp Lite IsoBar (ISOBAR4ULTRA) surge protector may be the answer you need to fix your treadmill interference problem.
To get around these issues, make sure the Treadmill is plugged into a Tripp Lite IsoBar (ISOBAR4ULTRA) surge protector on a different outlet and circuit from your TV. And then additionally, the HDTV may need to be plugged into a second Tripp Lite surge protector without other electronics (while testing).
If you are using extension cords, make sure the the cords are properly shielded.
Also make sure the the cords for the TV and Treadmill are not near each other. I'd also keep the treadmill cord away from the cable for the TV.
Keep in mind, also that LED light bulbs and CFL light bulbs can cause interference with a HDTV. So if you suspect that's the case, try changing the bulbs for older incandescent light bulbs.
It could also just be that your HDTV is made cheaply and / or is starting to go bad.