Any solution that's good for your health is going to cut into productivity. What companies are trying to do is find a solution that helps but doesn't disrupt that productivity. Unfortunately, I just don't think that's possible.
Currently, I've got a coworker who walks at a specialized treadmill, designed for office use, nearly all day long. Great for her, but all she does is read and type on her computer. There's some work you just can't be moving to do effectively. I design, requiring precision and focus. I can't stand or walk while I work. But my workload is such that I can't talk long breaks throughout the day.
A sensible approach might be several long breaks throughout the day. But the problem is fitting those in to a work day. I wouldn't want my work day to get longer. Sure, if you're single, it's easy to just lengthen your workday but fit in numerous breaks. However, not everyone has that freedom or desire. I want to be home with my family at a reasonable hour.
I think we need a more fundamental shift in corporate mentality. There's this persistent attitude of rushing to wait. Jam in a ton of work into a compressed timeframe only to have it languish once it's complete. On the other hand, there does need to be some kind of balance. You can't just have employees sit around doing nothing. Although, sometimes I feel like that's all that happens with so many of my clients.