to be honest, the 21k and 28k treadmills are just crap and just a waste of money.. You would find it quite hard to keep the track well aligned in the centre so that it doesnt rub against the frame and ultimately wear off or at the very least, get frayed from either of the ends... and once the track is gone, I dont believe you would get a replacement for that in the market (assuming its a 21k treadmill, which I really consider to be a disposible item)..
So, you're better off walking or running in some park, at least you would get to see some chicks every now and then and even have an opportunity to impress them with your masculinity