How much force goes into your leg when you use an elliptical machine? The device is praised by clinicians for being "low impact' but just how low is low?
I looked and looked but couldn't find any research about the loads delivered by an elliptical machine. Maybe some one knows. If so, please send it along. In the meantime, here's what I did to solve the problem.
I took a Lafayette Digital Muscle Tester and placed it under my right foot while on a Precor elliptical machine. I had to place a high density foam block under my other foot to make the pressure fairly equal under each foot (The digital muscle tester is a load cell. It records pressure applied to it.). I then set the resistance on the elliptical machine to a "moderate" level - between 8 and 10- and then used the machine for approximately ten repetitions.
When I got off the device, I looked at the force recorded by the digital muscle tester. It was 140 lbs. The muscle tester records peak force so this represented the maximum force that went into my leg.
I then repeated the procedure but increased the resistance setting on the machine to 12. This time, the peak force was 185 lbs.
I weigh 211 lbs. So, for me, this was 66% and 88% of body weight. The machine's resistance is a function of your body weight. If you weigh 150 lbs and exercise at the same setting and speed as I did, the load going into your leg will be a percentage of your body weight (probably close to 66% and 88%).
Of course, there are a few problems with my study. There was a "n" of 1. I didn't evaluate the relationship of load, resistance setting, and speed. The faster you move at any setting, the more resistance you get. And, I didn't have a continuous load curve to assess where in the arc of motion the load was the greatest. Someone with all of the right tools in a well equipped biomechanics lab could do this though.
But, what I do have is better than guessing; better than assuming that an elliptical is low impact so it's ok for people with joint disease or joint pain. It's ok as long as the client's load tolerance is at least 66% body weight.
This may explain why some people with knee, for example, tolerate the device and some don't. If the client's actual load tolerance for a Single Leg Squat or Stair Step (the elliptcal machine is close to these motions) is only 50% body weight, there's a good chance that the ellipitcal machine will be too much load.
Good reason to test the Load tolerance.
