Lower-Limb Myoelectric Calibration Postures for Transtibial Prostheses

Area of Science:

• Biomedical Engineering
• Rehabilitation Technology
• Biomechanics

Background:

• Myoelectric control of prostheses relies on muscle signal normalization and co-contraction identification.
• Previous research on posture's effect on lower-limb muscle activation is extensive in able-bodied individuals but limited post-amputation.

Purpose of the Study:

• To compare the impact of different calibration postures (seated, standing, dynamic) on user tracking performance.
• To investigate how these posture-dependent muscle activation relationships differ between able-bodied and transtibial amputee subjects.
• To determine optimal normalization strategies for myoelectric control.

Main Methods:

• A virtual tracking task was employed with 18 able-bodied and 9 transtibial amputee subjects.
• Surface electromyography (EMG) data were collected during seated and standing tracking postures.
• Three calibration postures (seated, standing, dynamic) were evaluated for their effect on EMG signal characteristics.

Main Results:

• Able-bodied subjects showed significant gastrocnemius (GAS) activation differences between seated and standing calibration, unlike tibialis anterior (TA).
• Transtibial amputee subjects exhibited no significant GAS or TA activation differences between seated and standing calibration.
• Normalizing EMG by the global maximum signal was found to be suboptimal for myoelectric control.

Conclusions:

• Body posture significantly influences muscle activation patterns in able-bodied individuals but less so in transtibial amputees.
• Calibration in both seated and dynamic postures is recommended for robust myoelectric control.
• Utilizing normalization data from seated posture and narrow co-contraction slopes from dynamic posture yields best results.