I have decided to purchase one of these devices expand-a-lung.com/ - it is now on it's way to me from the US. I have always felt strong when running , even long distances up to half marathon - but also feel that my lungs are my limiting factor. Whether it is the lungs themselves insofar as their ability to inhale and exhale sufficiently or my oxygen distribution system (basically my VO2max which is probably quite low) . I have read that most peoples lungs take in enough oxygen and it is their VO2 max which lets them down. Anyway, I recently met an older cyclist who told me that he had returned to cycling after a hedonistic life and found that a device like this helped him enormously. As far as I can make out you are simply inhaling and exhaling though a restriction which makes your respiratory muscles work harder while you are using the device. Looking forward to using it - I have read good reports about it.