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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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Effects of the number of SEMG channels used for training on joint torque estimation. (a) NRMSE. (b) .
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Figure 9: Effects of the number of SEMG channels used for training on joint torque estimation. (a) NRMSE. (b) .

Mentions: It is noteworthy that best performance was not consistently attributed to a single combination of muscles for the case of models trained with two channels. It is evident that models trained with five channels are superior to models trained with two. However models trained with eight channels do not have significant performance superiority. Figure 9 compares NRMSE and for different number of training channels.


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

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

Effects of the number of SEMG channels used for training on joint torque estimation. (a) NRMSE. (b) .
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 9: Effects of the number of SEMG channels used for training on joint torque estimation. (a) NRMSE. (b) .
Mentions: It is noteworthy that best performance was not consistently attributed to a single combination of muscles for the case of models trained with two channels. It is evident that models trained with five channels are superior to models trained with two. However models trained with eight channels do not have significant performance superiority. Figure 9 compares NRMSE and for different number of training channels.

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