Jack, a student in BIO 131, is the subject for this lab and has his EMG recorded

Question

Jack, a student in BIO 131, is the subject for this lab and has his EMG recorded during a maximal Contraction. To achieve a maximal contraction, he must lift 45 pounds. Six months later, after working out steadily and maintaining a healthy diet, Jack's muscles are notably bigger. He decides to try to elicit a new maximal contraction (and record the EMG), and is now able to lift 60 pounds. Questions: (2 Points) Compare the EMG recordings for Jack's maximal contraction before and after his 6 month training sessions. Circle the correct answer below: a) The EMGs will have the same amplitude b) The before EMG will have a larger amplitude c) The after EMG will have a larger amplitude 2. (3 Points) After his muscle growth, what would you expect Jack's EMG to look like if he lifted 45 pounds as he did before? Explain your answer in terms of motor unit recruitment. 3. (3 Points) Why were Jack's muscles notably bigger after his 6 month training period? What caused the increase in muscle size?

Explanation / Answer

Electromyography (EMG) is an electrodiagnostic medicine technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph, to produce a record called an electromyogram.

An electromyograph detects the electrical potential generated by muscle cells when these cells are electrically or neurologically activated. The signals can be analyzed to detect medical abnormalities, activation level, or recruitment order or to analyze the biomechanics of human or animal movement.

EMG, or electromyography, amplitude is the measure of the electric potential of motor units. Maximum EMG amplitude is more commonly referred to as maximum neuronal output. Studies have shown that maximum EMG amplitude increases with continual resistance training. These increases can range from minuscule to as much as a 50 percent increase after as little as a one-month training period. On average, at the end of a one-month period of consistent and repetitive resistance training, EMG amplitude reaches a plateau. Further increases in amplitude after this one-month period occur if the training regimen is varied.This plateau effect is assumed to occur as a result of sufficient neuronal adaptation to the resistance load. Variance in load or repetition causes the neuron to increase its output, and therefore EMG amplitude, to allow for increased muscular force of contraction after this plateau occurs.

1. THE AFTER EMG WILL HAVE A LARGER AMPLITUDE

2

The motor unit consists of a voluntary alpha motoneuron and all of the collective muscle fibers that it controls, known as the effector muscle. The alpha motoneuron communicates with acetylcholine receptors on the motor end plate of the effector muscle. Reception of acetylcholine neurotransmitters on the motor end plate causes contraction of that effector muscle.

Motor unit plasticity is defined as the ability of motoneurons and their respective effector muscles to physically and functionally change as a result of activity, age, and other factors. Motor unit plasticity has implications for improved athletic performance and resistance to immobility as a result of age. Recent advanced training techniques and physical therapy techniques that focus on improving neural function in addition to muscular function show promising results to improving athletic performances and extending mobility for the elderly

Resistance training has been shown to drastically increase performance of motor units of the larger muscle groups. Motor unit plasticity of the larger muscle groups is extremely important for athletes, especially those participating in high impact and fast pace sports such as track and field, martial arts, and American football. Training that focuses on improving muscle strength and neural function via resistance training, or more commonly known as plyometrics, is currently incorporated into many professional and collegiate training regiments. Motor unit plasticity can be measured in many ways, the most important of which being neural firing frequency, EMG amplitude, muscle force output, pre-synaptic inhibition, and synchronization.

Firing frequency is defined as the number of neuronal signals sent per second on one motoneuron. This frequency is measured in Hertz. Maximum firing frequency in humans typically ranges from 100

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