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Discharge characteristics of motor units during long contractions
Michael Pascoe, M.S.
Background
• Motor unit
• Functional quantum of the neuromuscular system
• Comprises an alpha MN, its axon, and all the muscle fibers it innervates
Research Questions
•How long can a human voluntarily activate a motor unit?
•How does the discharge behavior change with time?
Surface EMG
Abduction force
Fine wire SMU
Spike2 - Sample Data
100 s
0.75 V
1 V
5 %MVC
0.75 V
sEMG
Force
iEMG
MU
Flowchart
Interspike Intervals
Motor Unit Discharge Times
Filter Out Long Intervals (> 250 ms)
Filter Out Short Intervals (< 10 ms)
Divide Into 5 Equal Duration Epochs
Calculate Discharge Characteristics
Spike2 Data
SpikeStats.txt
mu_anal_longdur.m
Input
Epoch Boundaries
100 s
0.75 V
1 V
5 %MVC
0.75 V
sEMG
Force
iEMG
MU
epoch(1) epoch(2) epoch(3) epoch(4) epoch(5)
first spike last spike
Creating Equal Duration Epochsfor i = 1:length(dis) if (dis(i) < epoch1_end) epoch(1).values(j) = dis(i); j=j+1; elseif (dis(i) > epoch1_end & dis(i) < epoch2_end) epoch(2).values(k)=dis(i); k=k+1; elseif (dis(i) > epoch2_end & dis(i) < epoch3_end) epoch(3).values(l)=dis(i); l=l+1; elseif (dis(i) > epoch3_end & dis(i) < epoch4_end) epoch(4).values(m)=dis(i); m=m+1; elseif (dis(i) > epoch4_end & dis(i) <= dis(end)) epoch(5).values(n)=dis(i); n=n+1; endend
Create interspike intervals% Determine interspike interval in seconds isi(i).values = diff(epoch(i).values);
% Remove ISIs greater than 0.25 or less than 0.01 s (<4 or >100pps) isi(i).values = isi(i).values(find(isi(i).values<0.25 & isi(i).values>0.01)); sizeisifilt(i).values = size(isi(i).values);
Filter interspike intervals
Discharge Characteristics
• Mean discharge rate
• Standard deviation of discharge rate
• Coefficient of variation for discharge rate
• Standard error of the mean of discharge rate
• Mean interspike interval
• Standard deviation of interspike interval
• Coefficient of variation for interspike interval
Stein et al. Nat Rev Neurosci 2005, 6: 389-397
Output
Output
• A single text file (one trial)
• Subject initials and date preserved
• _SpikeStats.txt in place of _Times.txt
• Column headers in first row
• Output variable values in five rows
Output
Output
Trial Name Mean DR (pps-direct) Mean DR (pps-estimate) SD DR (pps) SEM DR (pps) CV DR (pps) Mean ISI (ms) SD ISI (ms) CV ISI (%) Start time (s) End time (s) Train Duration (s) Impulses (No.) ISIs (No.) ISIs <10ms ISIs >250ms ISIs removed
BKB_(11_21_2007)_Times 11.24653 11.228448 0.825317 0.825317 7.350231 89.059501 21.935176 24.629799 698.31423 753.63023 55.30595 622 621 0 0 0
10.682879 10.664742 0.797252 0.797252 7.475587 93.766922 22.891283 24.412963 753.63023 808.94623 55.13495 589 588 0 0 0
11.581364 11.722199 0.748408 0.748408 6.384536 85.308229 18.64768 21.859181 808.94623 864.26223 55.17485 639 638 0 2 2
9.844349 10.698871 1.000401 1.000401 9.350527 93.467804 28.586902 30.584759 864.26223 919.57823 55.15855 543 542 0 13 13
9.934456 10.455567 1.093795 1.093795 14.913897 92.346243 55.07046 40.389043 919.57823 974.89423 55.18775 39 38 0 46 46
ValidationEpoch(5) MATLAB Spike2
MeanDR (pps) 7.334067 7.33Std Dev DR (pps) 1.093795 1.09
CV DR (%) 14.913897 14.91
Mean ISI (ms) 136.35 136.35Std Dev ISI (ms) 55.07046 55.07
CV ISI (%) 40.389043 40.39
Start Time (s) 919.57823 919.578End Time (s) 974.89423 974.894Train Dur (s) 55.18775 55.188
No. Impulses 39 39No. ISIs 38 38
ISIs < 10 ms 0 0ISIs > 250 ms 46 46
In the near future...
•Analysis of surface EMG
•Analysis of index finger abduction force
•Distribution statistics for discharge times