**2. EMG electrodes and its types**

The bioelectrical activity inside the muscle of a human body is detected with the help of EMG electrodes. There are two main types of EMG electrodes: surface (or skin electrodes) and inserted electrodes. Inserted electrodes have further two types: needle and fine wire electrodes. The three electrodes (needle, fine wire and surface) are explained as follows. Among these three electrodes, surface EMG electrodes will be specifically discussed in detail as it pertains to the topic of this chapter.

#### **2.1. Needle electrodes**

Computational Intelligence in Electromyography Analysis – 428 A Perspective on Current Applications and Future Challenges

signal. A group of muscles are involved in a certain movement of the human body. The number of muscles recruited depends upon the activity in which the body is involved. E.g. in lifting a small weight such as a tiny pebble, fewer amount of muscles will be involved as compared to lifting a heavy mass like a 6 kg weight, where the muscles employed will be greater. In technical terms, whenever it is required to generate greater force, the excitation from the Central Nervous System increases, more motor units are activated and the firing

rate of all the motor units increase resulting in high EMG signal amplitudes [4,5].

**Figure 1.** A Motor Unit consists of one motor neuron and all the muscle fibers it stimulates [6]

rehabilitation, sports medicine and training, biofeedback and ergonomics research.

Electromyography enables us to generate force, create movements and allow us to do countless other functions through which we can interact with the world around us. The electromyograph is a bioelectric signal which has, over the years, developed a vast range of applications. Clinically, electromyography is being used as diagnostic tool for neurological disorders. It is frequently being used for assessment of patients with neuromuscular diseases, low back pain and disorders of motor control [7]. Other than physiological and biomechanical research, EMG has been developed as an evaluation tool in applied research, physiotherapy,

In the recent past, EMG has also found its use in rehabilitation of patients with amputations in the form of robotic prosthesis. EMG proves to be a valuable tool as it provides a natural way of sensing and classifying different movements of the body. A multi-degree of freedom robotic mechanism can effectively imitate the motion of the human limb. Recent advances in electronics and microcontroller technology have allowed improved control options for robotic mechanisms. One of the most vital advantages of microprocessor technology in robotic prosthetics is the advanced EMG filtering algorithms. Nowadays, control options are even available to those who were not at one time qualified for such prosthetic management.

Needle electrodes are widely used in clinical procedures in neuromuscular evaluations. The tip of the needle electrode is bare and used as a detection surface. It contains an insulated wire in the cannula. The signal quality from the needle electrodes is comparatively improved from other available types. Needle electrodes have two main advantages. One is that its relatively small pickup area enables the electrode to detect individual MUAPs during relatively low force contractions. The other is that the electrodes may be conveniently repositioned within the muscle (after insertion) so that new tissue territories may be explored [5]. A needle electrode is shown in Figure 2.

#### **2.2. Fine wire electrodes**

Wire electrodes are made from any small diameter, highly non-oxidizing, stiff wire with insulation. Alloys of platinum, silver, nickel, and chromium are typically used. Wire electrodes are extremely fine, they are easily implanted and withdrawn from skeletal muscles, and they are generally less painful than needle electrodes whose cannula remains inserted in the muscle throughout the duration of the test [5]. A fine wire electrode is shown in Figure 3.

Signal Acquisition Using Surface EMG and Circuit Design Considerations for Robotic Prosthesis 431

Disposable gelled EMG electrodes are most common; however, reusable gelled electrodes are also available. Special skin preparations and precautions such as (hair removal, proper gel concentration, prevention of sweat accumulation etc.) are required for gelled electrodes in order to acquire the best possible signal. Gelled EMG electrodes are shown in Figure 4.

Dry EMG electrodes do not require a gel interface between skin and the detecting surface. Bar electrodes and array electrodes are examples of dry electrodes. These electrodes may contain more than one detecting surface. In many examples, an in-house pre-amplification circuitry may also be employed in these electrodes. A reusable bar electrode is shown in Figure 5. Dry electrodes are usually heavier (>20g) as compared to gelled electrodes (<1g). This increased inertial mass can cause problems for electrode fixation; therefore, a material

There are two categories of surface EMG electrodes [5]: Passive and Active EMG electrodes.

These electrodes should be connected to an external amplification circuitry with the help of connecting wires for the proper acquisition of the EMG signal. Passive EMG electrodes can

**Figure 4.** Gelled EMG Electrodes

for stability of the electrode with the skin is required [10].

**Figure 5.** A Reusable Bar Electrode (an Example of Dry EMG Electrode)

*2.3.2.Categories of Surface EMG Electrodes* 

They are briefly explained as follows:-

*2.3.2.1. Passive EMG electrodes* 

be disposable or reusable.

*2.3.1.2. Dry EMG electrodes* 

**Figure 3.** Fine Wire EMG Electrode
