I'm using a Noraxon Telemyo telemetry unit and have been having a
problem with the
receiver shutting off during dynamic activities. I'm collecting from
four muscles
(anterior tibialis, medial gastrocnemius, vastus medialis, and lateral
hamstring)
with a ground on the fibular head. The receiver is connected via a
ribbon cable to
an A-D board, with data sampled at 1200 Hz with EVA software (Motion
Analysis Corp).
We collect force plate, kinematic, and EMG data simultaneously. We were

investigating the influence of ankle stirrup braces on EMG in subjects
with a
history of ankle sprain and had the subjects hopping sideways on the
instrumented
leg over a 6 inch high barricade. The signal recorded fine for 1-2
seconds (1-2 hops),
then the receiver would shut itself off. In reviewing the data that
were recorded before the unit shut off, there was no apparent clipping
or saturation of any of the channels (+/- 5 V range).

Technical support at Noraxon suggested that I unplug the ribbon cable
between the receiver and the A-D board, then do the movement while
simply watching the bar graph display on the receiver. When I did this,
the unit stayed on. As soon as I connected it back to the A-D board,
the problem reappeared. If I had the subjects produce a maximum
isometric contraction, there was no problem. It appears that the
problem is some interaction between the dynamic nature of the hopping
and the sampling characteristics of the A-D board, but I was not aware
that a signal could get "backed up" like a drain when alot of data were
being sampled.

Has anyone else had this problem? Can anyone explain what's causing the
problem and
how I can get around it? Unfortunately, I am constrained in my sampling
frequency
because the software will not allow me to sample at two different rates,
and I need
to sample the force plate at 1200 Hz.

Thank you.
--
Barbara Loitz-Ramage, PhD PT
McCaig Centre for Joint Injury and Arthritis Research
University of Calgary
3330 Hospital Dr. NW
Calgary, Alberta CANADA T2N 4N1
voice (403)220-4327; FAX (403)270-0617; email ramage@ucalgary.ca

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