Abstract
In this study, research was carried out on the end-effector force estimation of two representative multi-muscle contraction tasks: elbow flexion and palm-pressing. The aim was to ascertain whether an individual muscle or a combination of muscles is more suitable for the end-effector force estimation. High-density surface electromyography (HD-sEMG) signals were collected from four primary muscle areas of the upper arm and forearm: the biceps brachii (BB), brachialis (BR), triceps brachii (TB), brachioradialis (BRD), and extensor digitorum communis (EDC). The wrist pulling and palm-pressing forces were measured in elbow flexion and palm-pressing tasks, respectively. The deep belief network (DBN) was adopted to establish the relation between HD-sEMG and the measured force. The representative signals of the four primary areas, which were considered as the input signal of the force estimation model, were extracted by HD-sEMG using the principle component analysis (PCA) algorithm, and fed separately or together into the DBN. An index termed mean impact value (MIV) was proposed to describe the priority of different muscle groups for estimating the end-effector force. The experimental results demonstrated that, in multi-muscle isometric contraction tasks, the dominant muscles with the highest activation degree could track variations in the end-effector force more effectively, and are more suitable than a combination of muscles. The main contributions of this research are as follows: (1) To fuse the activation information from different muscles effectively, DBN was adopted to establish the relationship between HD-sEMG and the generated force, and achieved highly accurate force estimation. (2) Based on the well-trained DBN force estimation model, an index termed MIV was presented to evaluate the priority of muscles for estimating the generated force.
Highlights
It is challenging to measure the muscle force produced by skeletal muscle contraction accurately
When the multi-muscle contraction tasks were performed, High-density surface electromyography (HD-Surface electromyography (sEMG)) signals were collected from four primary areas of the upper arm and forearm
It should be indicated that the normalization was implemented among the four HDsEMG grids in each contraction cycle
Summary
It is challenging to measure the muscle force produced by skeletal muscle contraction accurately. The direct measurement method is commonly used for accurate determination of muscle force, wherein mechanical sensors are surgically placed in the tendons of skeletal muscles (Dennerlein et al, 1997; Finni et al, 1998; Huang and Gu, 2008). Indirect measurement methods, which are generally non-invasive, have been extensively employed to estimate the muscle force in related applications (Ayusawa et al, 2014; Martin et al, 2018). Ayusawa et al (2014) used a high-speed and high-precision video motion capture device to obtain human joint kinematic parameters. They established a mechanical equilibrium equation between the joint and muscle forces based on inverse kinematics (Ayusawa et al, 2014)
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