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Sandra Hirschberg
10-14-1996, 09:00 AM
Hello all

I am currently doing honours and am looking to quantify the
activation/strength deficit of the quadriceps muscle group of trained
athletes using electrical muscle stimulation (EMS). I will attempt to
quantify the activation deficit by getting subjects to do 2 trials
(randomised) of a MVC without EMS and 2 trials (randomised) of a MVC with
EMS and looking at the differences in peak forces produced.

I will stimulate the quadriceps using free form oval electrodes placed
transcutaneously on the quads.

I will be using a simple knee extension exercise on an isokinetic
dynamometer and have a number of questions, that I would appreciate some
feedback on, if anyone has any experience in this area.

1. would you recommend an isometric (static) or isokinetic(concentric or
eccentric) protocol? I am currently pilot testing both but would value your
input. Which is more RELIABLE?

2. If isometric at which angle? I thought of using 65 degrees.
If isokinetic at which velocity? I was going to use 120 degrees per
second, so as to make it somewhat sport-specific to sprint cyclists, (I
believe their knee velocity with sprint cycling is somewhere in this
vicinity, but would also appreciate any input on this).

3. I am placing the cathode proximal and the anode distal. Would it matter
if I placed the anode proximal and the cathode distal?

4. Do you know what sort of pulse properties would be best for producing
maximal force but minimal discomfort? (ie. pulse width, pulse train length,
frequency, etc).


5. Since I am pilot testing both isometric and concentric contraction
protocols, can you make a suggestion about the preload for the concentric
test? I am currently using 85% of max. isometric at a 90 degree knee angle
(starting position for concentric test), but am unsure if this is too high.
I know that torques produced are higher with greater preloads, but does it
matter if I keep it constant?. Maybe it would be easier to detect greater
increases in the torques with EMS with a smaller preload. Any suggestions?

6. Lastly I will be using 2 stimulators and 2 pairs of electrodes, because
one stimulator can only go to 100mA max. and I need to go higher than that.
So I will use the 2 stimulators to result in an additive effect of current
amplitude. My question would be how best to orientate the 2 pairs of
electrodes on the quads. Electrode size is 3" times 5". Have you any
suggestions?

Thanking you in advance for your help.
Kindest regards
Sandra
shirsc10@scu.edu.au