I have asthma triggered by VOC type chemicals. We have a side by side washer and dryer in a closet and I wanted to finish the floors in something that would not off gas. We went with marmoleum, a no VOC pseudo linoleum type product. Perhaps you could use that? I'm not sure though that it would prevent the weight from still damaging your floors?

You don't need a mat under a treadmill.

As Milly Rey states. The cork is all you need. The treadmill won't damage the cork. It might dimple it...but cork recovers from dimples. If you want proof, there is a simple test.

Take an off cut of the cork. Use the butt end of a screwdriver (or something round and hard) and PUSH into the cork (don't hit it...push the object into the cork). Put your weight behind it. Hold for several seconds (until your muscles shake). Now observe the dimple. It should be pretty deep. Good.

Now take a SUPER hot/wet cloth (as hot as you can handle...hot tap water is usually enough) and place the hot/wet cloth (it can be dripping wet...that's not a problem) and put it over the dimple. Use a bit of weight to hold it down (like a shoe) and go do something for 5 minutes.

Come back and remove the cloth from the cork (cloth should be cool to the touch). Now look at the dimple once again. It will have improved by 50% - 100%. If there is still a dimple, simply repeat the hot cloth trick until it is removed.

Tah Dah! Cork floor has been fixed. That's why you don't worry about heavy items sitting on a cork floor.

Enjoy your cork floor and your work out room.

But how do you find a non toxic treadmill is the question?? They all hsve PVC and Phthalates

Just saw one comment i was going to say.. the treadmill itself is loaded with toxins the entire belt is pvc loaded which gas off for years

all formaldyhyde and toxins