The primary issue with the ineffectiveness of the treadmill as a means of harvesting human power is that you have to PUSH against something to make the belt move. This means that the upper body is engaged as well, rather needlessly, pushing against the hand rails.

I tried to fix this by setting the incline as high as possible, but still, the friction of the belt was too high and I had to push against the rails. 

Since I am a road cyclist having done a couple 100K rides, I know all too well that cycling is one of the most efficient forms of extracting power from humans. So, I took the treadmill motor out and made a bike trainer with the same electronics. 

I'm still finding that it's too difficult to power the TV, and at this point, I'm fairly certain that the issue is the motor. It's simply not efficient enough. So, the next steps will be to try out different motors, and make the bike generator more efficient.