I am a former Marine, marathoner, and Ironman triathlete who lost the ability to run a few years ago because of knee and hip damage (I guess I shouldn't have been surprised). A friend of mine who is an ultramarathoner and mechanical engineer built me a new kind of bicycle that basically lets me run outdoors without impact. Here is a photo of me on it in Arpil at the start of the Rosarito to Ensenada 50 mile ride, my first endurance event since about 2003. We have a website with a video and would love to get feedback from other runners to get a sense of whether there are other people out there who might be interested in using these for cross-training or as a substitute for running. Please go to http://www.elliptigo.com/ for the video and to let us know your thoughts through our survey. Really appreciate it and happy running . . .
Thats a wonderful machine. I certainly appreciate your service to our country.
People tend to think of impact in a detrimental light, but there is some evidence that compressive loading of the femur may be beneficial for limiting the incidence of fractures.
Last fall there was an interesting discussion on this correlation in the BIOMCH-L discussion group. You might look it up, if you are interested.
As I recall several researchers cited a study that indicated that elderly people who engaged in high impact exercises, like running where there is an aerial phase to the gait cycle, have a lower incidence of hip fractures than the control group that followed a walking regiment.
There was also a NASA study a few years ago that caused them to change their exercise program on the station. That is why astronauts now exercise on a treadmill with heavy elastic chords pulling them onto the tread.
Way back there was a Russian astronaut who spent more than a year in space who did not follow a similar exercise program. I think that he had all sorts of bone fractures when he returned to earth. It may have been a matter of bone strengthening and not bone density. I dont remember.
In any event, impact may not always be disadvantageous; it may enhance bone matrix alignment.
Good luck in your program,
Semper Fi Bro.. I like the new ellipticals which emulate running more than the ones which emulate skiing. The video was most helpfull in seeing the actual use. Like you I like to ride but this would really help the runner in a more specific way for cross training