Humac Norm Troubleshooting

[Carlie Jones]

I am working with a Human Norm (dynamometer) to test the torque of ankle orthotics. Below is the graph of our results for torque vs angle of the orthotic, and I am having some issues interpreting the data (please ignore the initial noise on the graph, we haven't removed the first trial yet). The ankle went from 20 degrees of plantarflexion up to neutral (0 degrees), and back 10 times. What I don't understand is why there is the zero torque moment at around 11 degrees.

I was wondering if anyone on here had any experience working with a Human Norm (or Biodex) and could provide any insight into the graph. Thanks!

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[Tim Wrigley]

Re: Humac Norm Troubleshooting

Difficult to say without knowing how your ankle orthosis is attached to the dynamometer. What is the orientation of attachment fixture and orthosis ? Are you recording a torque v angle curve with just the attachment fixture first, and subtracting that (gravitational?) torque from the orthotic + fixture curve ?

Tim Wrigley
University of Melbourne

[Carlie Jones]

Re: Humac Norm Troubleshooting

The AFO is on a participant's foot placed on a footplate attached to the dynamometer. The test starts with the foot at peak dorsiflexion, and runs to peak plantarflexion and back. Additionally, the dynamometer corrects for gravity during the collection, and the graphs should represent that adjusted torque. We are ultimately going to run the test with the person in the AFO and then in just their shoe and subtract to get just the AFO torque vs angle curve, but the shape should be roughly the same (?)

[Douglas Powell]

Re: Humac Norm Troubleshooting

Carlie,
We use the HUMAC dynamometer to measure ankle passive resistance torques during continuous passive motion as well. You can see our plots below.

Without knowing your dynamometer setup (prone vs. supine), it would appear that the direction of the resistance torque changes directions as 11 degrees. Note that when running the dynamometer for the supine position on the right limb, DF is negative rather than positive. We correct for this in MATLAB. If you are in either position, consider if the 11 degree ankle position is actually associated with the point at which the foot is vertically oriented. If this were the case, it could cause your resistance torque to change directions based on gravity.

In our study we plot ankle position-time, torque-time and torque-angle for our analyses. If we can be of greater support, please feel free to email me at Douglas.powell@memphis.edu.


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