Raw Data

Trial 1

Trial 2

Dave 439.4 550.5

Megan 271.8 415

Jeremiah 199.1 333.8

Dianna 785.2 1021

Ogechi 215.2 351.4

Ambar 238.3 244.3

Difference scores of raw data

Trial 2-1

111.1

143.2

134.7

235.8

136.2

6

Trial 2-1

Change in mean 127.83

Lower conf limit 67.23

Upper conf limit 188.43

Typical error 52.09

Lower conf limit 35.01

Upper conf limit 108.83

Total error 102.14

Limits of agreement 144.29

Pearson r 0.981

Intraclass r 0.958

Can you directly compare EMG amp between subjects?Can you directly compare EMG amp between subjects?

Reproducibility of surface EMG Reproducibility of surface EMG variables and peak torque during variables and peak torque during

three sets of ten dynamic three sets of ten dynamic

contractionscontractions

BarbroBarbro Larsson Larsson , , BjarneBjarne MånssonMånsson , , Christian Karlberg , Peter Syvertsson , Christian Karlberg , Peter Syvertsson ,

Jessica Elert and Björn Gerdle Jessica Elert and Björn Gerdle

IntroductionIntroduction

Isokinetic dynamometers are commonly Isokinetic dynamometers are commonly used for assessment of dynamic muscle used for assessment of dynamic muscle strength, endurance and fatigue.strength, endurance and fatigue.

For measurement of reproducibility, intra-For measurement of reproducibility, intra-class correlation (ICC) is preferred. class correlation (ICC) is preferred.

Fatigue and EMGFatigue and EMG

Peripheral muscle fatigue during sustained Peripheral muscle fatigue during sustained static contractions is generally static contractions is generally characterized by increases in signal characterized by increases in signal energy (RMS or iEMG) and shifts in the energy (RMS or iEMG) and shifts in the EMG spectrum towards lower frequencies EMG spectrum towards lower frequencies (spectral shift).(spectral shift).

Fatigue increases amplitudeFatigue increases amplitudeFatigue decreases frequencyFatigue decreases frequency

Problems with Dynamic Problems with Dynamic Contractions and EMGContractions and EMG

The interpretation of the EMG from dynamic The interpretation of the EMG from dynamic contractions might be difficult—especially for contractions might be difficult—especially for frequency spectrum variables—because the frequency spectrum variables—because the movement per se introduces additional factors movement per se introduces additional factors that might affect its characteristicsthat might affect its characteristics

changes in force throughout the range of motionchanges in force throughout the range of motion changes in fiber and muscle lengthchanges in fiber and muscle length movement of the neuromuscular junction with movement of the neuromuscular junction with

relation to the electrodes positionrelation to the electrodes position problems with non-stationary of the signal problems with non-stationary of the signal

(recruitment and de-recruitment of MUs (recruitment and de-recruitment of MUs

Methods -- IsokineticMethods -- Isokinetic

3 sets of 10 isokinetic contractions at 90 d/s3 sets of 10 isokinetic contractions at 90 d/sOne hour between setsOne hour between setsThe electrodes were NOT REMOVEDThe electrodes were NOT REMOVEDROM was constrained to 90 – 15 deg ext.ROM was constrained to 90 – 15 deg ext.Subjects relaxed during knee flexion and Subjects relaxed during knee flexion and

the immediately performed extension.the immediately performed extension.

Methods -- EMGMethods -- EMG

Surface EMG from VL, VM & RFSurface EMG from VL, VM & RF20 mm interelectrode distance on center of 20 mm interelectrode distance on center of

muscle in line with muscle fibers.muscle in line with muscle fibers.Sampled at 2KHz with 12 bit A/DSampled at 2KHz with 12 bit A/DEMG band pass filtered at 16-500 HzEMG band pass filtered at 16-500 HzTorque & Position low pass filtered at 40 HzTorque & Position low pass filtered at 40 Hz

EMG Processing & StatisticsEMG Processing & Statistics

FFT with Hamming window (2 Hz resolution)FFT with Hamming window (2 Hz resolution)RMS used for amplitudeRMS used for amplitudeSignal-amplitude ratio (SAR) of relaxation Signal-amplitude ratio (SAR) of relaxation

(flexion phase) to contraction (extension (flexion phase) to contraction (extension phase).phase).

ICC (3,1) Shrout & FleissICC (3,1) Shrout & FleissOne-way ANOVA was used to test for One-way ANOVA was used to test for

differences between sets.differences between sets.

ResultsResults

No significant differences between the No significant differences between the three sets.three sets.

Peak torque had high reproducibility (0.99) Peak torque had high reproducibility (0.99) Rectus femoris generally had lower ICC Rectus femoris generally had lower ICC

than the two other muscles than the two other muscles RMS generally had somewhat higher ICC RMS generally had somewhat higher ICC

than the MNF than the MNF

DiscussionDiscussion

High ICC may be due to limited ROM High ICC may be due to limited ROM which may control movement effects.which may control movement effects.

Previous studies have reported good Previous studies have reported good reproducibility for during and between day reproducibility for during and between day static contractions.static contractions.

Not REMOVING ELECTRODES may Not REMOVING ELECTRODES may have contributed to high ICChave contributed to high ICC

Discussion -- ContDiscussion -- Cont

We have reported that the MNF We have reported that the MNF correspond to physiological properties correspond to physiological properties during dynamic contractions during dynamic contractions

Positive significant correlations have been Positive significant correlations have been reported between the proportion of Type-II reported between the proportion of Type-II muscle fibers and MNF during single muscle fibers and MNF during single dynamic (non-fatiguing) contractionsdynamic (non-fatiguing) contractions