The Kelsey Report

Why Does My Knee Hurt On An Elliptical Machine?

A client once asked me, “You know, I don’t get why my knee hurts when I’m using an elliptical machine. I thought those things were supposed to be low impact, right? So, what’s the deal?”

Clinicians and trainers praise elliptical machines for being a good alternative “low impact” exercise for people with joint pain.

But how low, is low?

I 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 figure it out.

I took a Lafayette Digital Muscle Tester and placed it under my right foot while on a Precor EFX 546i 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.

At the time of the test, I weighed 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 because elliptical is low impact, it’s ok for people with joint disease or joint pain.

Why Your Knee May Hurt On A Low Impact Machine

Most physical ailments – musculoskeletal problems – come down to this principle: when physical demand exceeds physical capacity, symptoms follow.

Your ability to withstand a certain amount of force with good form is what I refer to as “load tolerance”. People who have knee pain usually have a load tolerance equal to less than their body weight. So, for example, if your knee hurts while walking or running, you may find that in a pool, where you effectively weigh less from the buoyancy of the water, you may not hurt at all. This is because the load tolerance of your joint(s) is greater than the load your joints experience in the water.

An elliptical machine feels ok as long as your load tolerance is at least 66% body weight (and it could be an reasonable option while re-training a stubborn Runner’s Knee).

A Simple Test

If  your  load tolerance for a Single Leg Squat or Stair Step (the elliptical machine is close to these motions) is only 50% body weight, there’s a good chance that the elliptical machine will be too much load. This may explain why some people with knee pain, for example, tolerate the device and some don’t.

A simple test to help you determine if an elliptical might be a good choice is the Back Slider test in the video below. If you can perform this test, you will likely not have difficulties with an elliptical machine.

The password is fusiontribe.

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Linda Hendrex says

I’m not sure I understand the point of the test. Wouldn’t it make more sense to simply get on an elliptical machine and move for a few minutes to determine if this exercise is right or wrong for you? If it hurts, stop, and if it doesn’t hurt, then this exercise is OK to do?

I have osteoarthritis in both knees, coupled with a torn cartilage in my right knee. Swimming, walking, ski machine, and running seem to aggravate the pain in my right knee so I do not do those activities, but an elliptical gives me a great cardio workout and my knees stay comfortable with no apparent after effects. Biking , Total Gym, and the elliptical are my exercises of choice, but I could not tolerate the tests in this article at all. By those standards, I should not be using an elliptical machine.

I tend to go by the rule that “if it hurts don’t do it”, but “if it doesn’t hurt then it is a healthy and constructive thing to do”. Am I misunderstanding my body’s signals? Do you think that if I cannot tolerate this test that the elliptical will cause further damage to my knees even though the exercise itself is comfortable in the short term?

It is important for me to know because I am about to invest in purchasing an elliptical machine for my home gym and do not want to spend the money if I won’t be able to use it long term. Not to mention that my knees need to get better and not worse! If you could expand some on the significance of testing as opposed to “doing what doesn’t hurt and avoiding what does hurt” it would help me decide if I should purchase one of these machines or not. Thanks for any further information you could give!

    DD Kelsey says

    Hello Linda –

    Thanks for your comments and questions.

    The purpose of the test was to help people understand WHY their knee might hurt on what is promoted as a “low impact” exercise option and to point out the range of loading that takes place with an elliptical machine. In your case, it may be that the arc of motion of the elliptical machine you use does not expose your joint to too much force. The Back Slider test is an option for people who might be wondering about their own knee capacity.

    One of the challenges with osteoarthritis is that sometimes pain shows up later; after an activity. So, yes, generally, if something hurts and it feels like a joint related pain, then you have to either modify the activity or avoid it until your body gets stronger.

Victor says

Im trying to beat my long term runners knee, and I read online that doing the crosstrainer backwards might help. Low and be hold damn I could feel those quads, including the vmo fire. Think this is great for a “functional” exercise since I can’t do squats yet etc.

    DD Kelsey says

    Victor –

    Thanks for your comments and thoughts. There was a study done at Willamette University in Oregon that looked at muscle activity during forward or backward movement of the limb on an elliptical machine. They found the quads to be more active when using the machine in the reverse mode and the hip muscles was well. Since the hip muscles have a reflexive connection with the quadriceps (and isolating the VMO isn’t possible since the muscle is part of the quadriceps and is innervated by one nerve), by increasing the hip activity, the quadriceps activity increases as well.
    You might enjoy my book, “The Runner’s Knee Bible” as a resource for your efforts in overcoming your runner’s knee issue. It has helped a lot of people. http://www.runnerskneebible.com
    Good luck!
    DK

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