Emg Activity : Visible Muscle Activation

Ever wondered how workout plans get designed to target various muscle groups? How does your trainer prescribe different exercises for different muscles? Wait! Is that even a valid question? You feel it in your muscles when you exercise, don't you? Of course, but how do we know which exercise would better target a given muscle group when comparing two or more exercises of the same kind? Is there a way to visualize muscle activation in real time? Read more to know how an EMG can capture muscle activity.

What is EMG?

It is the most minimally invasive biomedical procedure that examines signals received by muscles from the nerves. When I say minimally invasive it means that there are 2 different ways of reading the signals, either by placing electrodes above the skin or inserting needle like electrodes inside the muscle to capture the reading. EMG basically monitors and records signals between motor neurons and the muscle. The result could also be used to identify whether the muscle under inspection is damaged or healthy. For readers who would like to know, EMG stands for Electromyography. 

Let's proceed to gain understanding on how the entire setup works in coordination to secure an EMG reading. Before we start you should be aware of the following terms to keep the information inflow smooth.

• Motor Neuron : A nerve cell located in the spinal cord that supplies nerve connections to the skeletal muscles.
• Motor Unit : A connection between a motor neuron and the muscle fibers it connects to.

Process flow of the EMG technique

1. Motor neuron sends signal to the connected muscle to contract
2. EMG device reads electrical pulses and records them
3. A connected computer uses modern human computer interaction to capture this information and creates a tabular output or plots a graph.
4. This graph may be further analyzed by a doctor 

Let's take an example to better understand things. John is facing some neuromuscular disorder in his left arm. He visits a doctor and the doctor prescribes him an EMG test. Next for the EMG test, a technician carefully places a needle into John's left arm muscle. John is then asked to contract the muscle. As the muscle contracts, the electrode picks up the electrical signal and records it. A connected computer then uses this recorded information to plot a graph representing electrical signals and muscle activity. This is displayed on the oscilloscope (monitor). Additionally, there is a provision to listen to the signal using an audio amplifier. It makes a "ting" sound effect every time the muscle under inspection contracts.

Now that we know how it works, we shall see where could this be applied in real life. This technique could be deployed in the following circumstances:

1. Nerve abnormalities
2. Muscle dysfunction
3. Disruption in nerve-muscle connection (Myasthenia Gravis condition)
4. Studying sports movements and Exercise physiology

Now the most common question, does this have any side effect? To answer this, the only side-effect that you could point out would be muscle soreness for sometime due to needle insertion. If you've ever wondered how well a lat pull down targets your lats or how effective are seated dumbbell curls for your biceps, an EMG activity report could make this clear. It is capable of showing the pattern in which the  muscle fibers get recruited when a particular muscle group is placed under significant stress.

Points to Note:

1. Voltage is always measured between the positive and negative inputs (electrodes)
2. Three electrodes are used to perform a EMG test. 

• Positive Electrode - placed on the muscle to be analyzed
• Negative Electrode - placed on the muscle to be analyzed
• Ground Electrode(Reference) - placed on a rested part like edge of  a bone. (wrist)

1. An accelerometer could be used to measure muscle tremor or muscle tension when the muscle is not moving. Ideally, a healthy muscle does't produce an EMG signal when at rest. 
2. Differential recording technique is used to determine  and separate external electrical noise coming from the environment.

Differential Recording Technique for Noise Cancellation

The signal captured by the EMG device may get misinterpreted due to adulteration with the electrical noise form the environment. To differentiate actual signal from the environmental noise differential recording technique is used. Both the positive and negative electrodes pick up significantly different readings. Since they are placed near to each other, clear difference in readings can be figured out. The environmental noise is identified by weak electrical signals captured by the EMG device. Since the noise gets captured from far off environment, the intensity of all noise signals is comparatively low and similar to each other. Hence, they could be collectively eliminated.