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Comparison of regression models for estimation of isometric wrist joint torques using surface electromyography.

Ziai A, Menon C - J Neuroeng Rehabil (2011)

Bottom Line: It was shown that mean adjusted coefficient of determination (Ra2) values decrease between 20%-35% for different models after one hour while altering arm posture decreased mean Ra2 values between 64% to 74% for different models.Therefore model retraining is crucial for preserving estimation accuracy.Data resampling can significantly reduce model training time without losing estimation accuracy.

View Article: PubMed Central - HTML - PubMed

Affiliation: MENRVA Research Group, School of Engineering Science, Faculty of Applied Science, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada.

ABSTRACT

Background: Several regression models have been proposed for estimation of isometric joint torque using surface electromyography (SEMG) signals. Common issues related to torque estimation models are degradation of model accuracy with passage of time, electrode displacement, and alteration of limb posture. This work compares the performance of the most commonly used regression models under these circumstances, in order to assist researchers with identifying the most appropriate model for a specific biomedical application.

Methods: Eleven healthy volunteers participated in this study. A custom-built rig, equipped with a torque sensor, was used to measure isometric torque as each volunteer flexed and extended his wrist. SEMG signals from eight forearm muscles, in addition to wrist joint torque data were gathered during the experiment. Additional data were gathered one hour and twenty-four hours following the completion of the first data gathering session, for the purpose of evaluating the effects of passage of time and electrode displacement on accuracy of models. Acquired SEMG signals were filtered, rectified, normalized and then fed to models for training.

Results: It was shown that mean adjusted coefficient of determination (Ra2) values decrease between 20%-35% for different models after one hour while altering arm posture decreased mean Ra2 values between 64% to 74% for different models.

Conclusions: Model estimation accuracy drops significantly with passage of time, electrode displacement, and alteration of limb posture. Therefore model retraining is crucial for preserving estimation accuracy. Data resampling can significantly reduce model training time without losing estimation accuracy. Among the models compared, ordinary least squares linear regression model (OLS) was shown to have high isometric torque estimation accuracy combined with very short training times.

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Sample torque signal.
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Figure 4: Sample torque signal.

Mentions: Eleven healthy volunteers (eight males, three females, age 25 ± 4, mass 74 ± 12 kg, height 176 ± 7 cm), who signed an informed consent form (project approved by the Office of Research Ethics, Simon Fraser University; Reference # 2009s0304), participated in this study. Each volunteer was asked to flex and then extend her/his right wrist with maximum voluntary contraction (MVC). Once the MVC values for both flexion and extension were determined, the volunteer was asked to gradually flex her/his wrist to 50% of MVC. Once the 50% was reached the volunteer gradually decreased the exerted torque to zero. This procedure was repeated three times for flexion and then for extension. Finally the volunteer was asked to flex and extend her/his wrist to 25% of MVC three times. Figure 4 shows a sample of torque signals gathered. Positive values on the scale are for flexion and negative values are for extension.


Comparison of regression models for estimation of isometric wrist joint torques using surface electromyography.

Ziai A, Menon C - J Neuroeng Rehabil (2011)

Sample torque signal.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3198911&req=5

Figure 4: Sample torque signal.
Mentions: Eleven healthy volunteers (eight males, three females, age 25 ± 4, mass 74 ± 12 kg, height 176 ± 7 cm), who signed an informed consent form (project approved by the Office of Research Ethics, Simon Fraser University; Reference # 2009s0304), participated in this study. Each volunteer was asked to flex and then extend her/his right wrist with maximum voluntary contraction (MVC). Once the MVC values for both flexion and extension were determined, the volunteer was asked to gradually flex her/his wrist to 50% of MVC. Once the 50% was reached the volunteer gradually decreased the exerted torque to zero. This procedure was repeated three times for flexion and then for extension. Finally the volunteer was asked to flex and extend her/his wrist to 25% of MVC three times. Figure 4 shows a sample of torque signals gathered. Positive values on the scale are for flexion and negative values are for extension.

Bottom Line: It was shown that mean adjusted coefficient of determination (Ra2) values decrease between 20%-35% for different models after one hour while altering arm posture decreased mean Ra2 values between 64% to 74% for different models.Therefore model retraining is crucial for preserving estimation accuracy.Data resampling can significantly reduce model training time without losing estimation accuracy.

View Article: PubMed Central - HTML - PubMed

Affiliation: MENRVA Research Group, School of Engineering Science, Faculty of Applied Science, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada.

ABSTRACT

Background: Several regression models have been proposed for estimation of isometric joint torque using surface electromyography (SEMG) signals. Common issues related to torque estimation models are degradation of model accuracy with passage of time, electrode displacement, and alteration of limb posture. This work compares the performance of the most commonly used regression models under these circumstances, in order to assist researchers with identifying the most appropriate model for a specific biomedical application.

Methods: Eleven healthy volunteers participated in this study. A custom-built rig, equipped with a torque sensor, was used to measure isometric torque as each volunteer flexed and extended his wrist. SEMG signals from eight forearm muscles, in addition to wrist joint torque data were gathered during the experiment. Additional data were gathered one hour and twenty-four hours following the completion of the first data gathering session, for the purpose of evaluating the effects of passage of time and electrode displacement on accuracy of models. Acquired SEMG signals were filtered, rectified, normalized and then fed to models for training.

Results: It was shown that mean adjusted coefficient of determination (Ra2) values decrease between 20%-35% for different models after one hour while altering arm posture decreased mean Ra2 values between 64% to 74% for different models.

Conclusions: Model estimation accuracy drops significantly with passage of time, electrode displacement, and alteration of limb posture. Therefore model retraining is crucial for preserving estimation accuracy. Data resampling can significantly reduce model training time without losing estimation accuracy. Among the models compared, ordinary least squares linear regression model (OLS) was shown to have high isometric torque estimation accuracy combined with very short training times.

Show MeSH
Related in: MedlinePlus