Reliability Of Lower Limb Surface Electromyography Calibrated By Standard Isometric Contraction In Elderly Patients With Knee Osteoarthritis

Objective: Normalization is one of the necessary processes in processing surface electromyography(s EMG)signals and plays an important role in comparing and analyzing s EMG signals.Maximum voluntary isometric contraction(MVIC)is the most commonly used s EMG normalization method at present,but MVIC is affected by motivation level.Pain is one of the most important clinical symptoms for patients with Knee osteoarthritis(KOA).In order to avoid pain,patients with KOA may have a weak motivation to perform MVIC test,which may lead to inconsistent torque generated by multiple maximum isometric contractions in patients with KOA,thus affecting the retest reliability.At present,there are few studies on s EMG normalization methods for pathological population,and no s EMG normalization methods specifically for KOA patients have been found.So.In this study,a new standardized method was designed,namely,standard isometric contraction(SIC),which requires only muscle anti-gravity isometric contraction and is less affected by pain,which may be more suitable for patients with KOA.The purpose of this study was to evaluate the retest reliability of SIC test and MVIC test in KOA patients,and to compare the retest reliability of the two normalization methods applied to KOA patients while level walking.Methods: The preliminary selection of subjects was done by distributing leaflets in the local community and conducting questionnaires and interviews with the elderly.The subjects were further screened by clinical signs and imaging diagnostics.Finally,35 subjects successfully completed the experiment and were included in the study analysis.The subjects were required to complete the level walking test,the SIC test and the MVIC test in sequence,and to return to the laboratory one week later to repeat these tests.A three-dimensional infrared motion capture and analysis system(Vicon Motion Analysis Inc,Oxford Metrics Ltd,UK),a three-dimensional ergometer(Kistler Instruments AG Corp,Winterthur,Switzerland,size 90 x60 x 10 cm)and a wireless(Noraxon,Boston,USA)for simultaneous acquisition of kinematic,kinetic and electromyographic data from KOA patients performing ambulation tests.The Noraxon was used to collect EMG data from KOA patients performing SIC and MVIC tests on the gluteus maximus,semitendinosus,rectus femoris,lateral femoris,tibialis anterior,lateral gastrocnemius and soleus muscle.Intra-class correlation coefficients(ICC)and 95% confidence intervals were used to assess the relative reliability of the two normalization methods,and standard error of measurement(SEM)was used to assess the absolute reliability of the two normalization methods.Results:(1)In the SIC tests,the retest reliability was good for all 7muscles(ICC=0.749-0.863,SEM=4.81-11.78);in the MVIC tests,the retest reliability was good for the gluteus maximus and semitendinosus(ICC=0.767-0.785,SEM=14.33-26.06),the rectus femoris,lateral femoris,anterior tibialis,lateral The retest reliability of all seven muscles in the SIC test was higher than that of the MVIC test;(2)after standardization by SIC,the retest reliability of the rectus femoris,lateral femoris,anterior tibialis,lateral gastrocnemius,and flounder muscles was good(ICC=0.713-0.845,SEM=0.845).0.845,SEM=0.11-0.23),and average reliability for the gluteus maximus and semitendinosus muscles(ICC=0.666-0.669,SEM=0.12-0.13);whereas,after standardization by MVIC,average reliability for the gluteus maximus,semitendinosus,lateral femoris,anterior tibialis,lateral gastrocnemius,and soleus muscle(ICC=0.534-0.652).The retest reliability of all seven muscles normalized by SIC was higher than that normalized by MVIC,and the retest reliability of the rectus femoris muscle normalized by SIC was significantly higher than that normalized by MVIC;(3)KOA patients performing SIC The EMG values of the lower extremity muscles during the test were closer to those during level walking,and the EMG values of most of the muscles during the execution of the MVIC test far exceeded their EMG values during level walking,and the peak EMG values of the lateral femoral,lateral gastrocnemius and flounder muscles exceeded 100% of the MVIC during level walking in KOA patients.Conclusion:(1)For KOA patients,SIC is a normalization method with good retest reliability,and is more suitable for normalizing electromyography of KOA patients than MVIC during level walking,which has good clinical promotion potential;(2)The retest reliability of MVIC normalization method in KOA patients was moderate,and the electromyography of KOA patients normalized by MVIC method during level walking tended to overestimate the percentage of muscle activation.Therefore,it is recommended that clinical staff and researchers use SIC to normalize the lower limb surface electromyography in KOA patients,and use MVIC cautiously to normalize the electromyography in KOA patients or other pathologic patients with pain symptoms.