Question 1

A 75 kg female powerlifter is performing a back squat with a bar and weights totalling 130 kg. The combined weight of her body, the bar and the weight plates is equally distributed over both feet. If the sum of the pressures under the left and right feet is 167.588 kPa, what is the size of the contact area under the feet?

Accepted Answer

The answer of A 75 kg female powerlifter is performing...

Question 2

The detected signal resulting from the depolarisation wave as it propagates in both directions along a single muscle fibre from its motor end plate is referred to as the:

Accepted Answer

A MAP is related to a single muscle fibre, whereas the other definitions are related to more than one fibre.

Question 3

The biceps brachii contains approximately 600 000 muscle fibres distributed between 750 motor units. What is the innervation ratio of the muscle?

Accepted Answer

The innervation ratio is obtained by dividing the number of muscles fibres by the number of motor units in the muscle.

Question 4

Which is usually the highest amplitude of the electromyographical signal recorded at the skin surface (i.e. before amplification)

Accepted Answer

It is generally accepted that the peak amplitude of the raw EMG recorded using surface electromyography does not exceed 5 mV and that its frequency spectrum is between 0-1000 Hz.

Question 5

Why are two electrodes usually used to record the electromyographic signal at the skin surface?

Accepted Answer

Differential EMG amplifiers subtract the signal detected by one recording electrode from the signal detected from the second recording electrode. By removing the common signal detected by the two electrodes, external sources of noise can be attenuated.

Question 6

An electromyogram recorded using two 10 mm x 1 mm bar electrodes may contain signals from approximately how many motor units (MUs)?

Accepted Answer

The majority of sport and exercise science applications use surface electrodes which, depending on their size, can detect the signal from thousands of muscle fibres belonging to many (e.g., 20-50) different motor units.

Question 7

When a raw EMG is processed to derive the Average Rectified EMG value (ARV), the length of the time window over which the signal is 'averaged' should be?

Accepted Answer

Calculation of the ARV involves first reversing all of the negative phases of the raw EMG (full-wave rectification). The integral of the rectified EMG is then calculated over a specific time period, or window (T), and the resulting integrated EMG is finally divided by T to form the ARV. For this calculation, the duration (or width) of successive time windows (T) is selected by the investigator and can vary between 10 to 200 ms, depending on the duration and nature of the raw EMG.

Question 8

When a raw EMG is processed to derive the Average Rectified EMG value (ARV), what effect does increasing the length of the time window over which the signal is 'averaged' (e.g. from 50 ms to 100 ms) have on the final processed EMG?

Accepted Answer

Selection of short duration window widths (e.g. 10-50 ms) in the ARV calculation may allow the detection of rapid alterations in activity, but the resulting curve will still resemble the rectified EMG. Adoption of longer widths (e.g. 100-200 ms) will reduce the variability of peak amplitudes, but the resulting curve will lose the trend of the underlying EMG.

Question 9

Which of the heads of the triceps could electrical activity not reliably be recorded from using surface electromyography?

Accepted Answer

The medial head is not superficial, and the dead and short heads do not exist.

Question 10

Normalising EMGs is often performed by:

Accepted Answer

Normalisaton is performed by dividing the task EMG from a reference signal from the same muscle, which can be maximal or submaximal depending on the circumstances.

Question 11

The main purpose of normalising EMGs is to allow comparison with those from other muscles and/or people:

Accepted Answer

The amplitude of EMGs recorded from the same muscle on different occasions, or from different muscles and different individuals, cannot be compared directly; even if they have been processed using the same method. This problem can be solved by normalising EMGs after they have been processed by expressing the task-specfic EMGs as a percentage of the peak EMG values derived from a reference task (e.g. maximum voluntary contraction).

Question 12

The term isokinetic means

Accepted Answer

Isokinetic is a term used to describe a situation where there is a muscle contraction during movement, but the rate of the movement is held at a constant pre-determined angular velocity

Question 13

The term isometric means

Accepted Answer

Isometric testing involves the muscles being testing while no movement of the lever arm takes place

Question 14

The term Isotonic means

Accepted Answer

isotonic testing is when the muscle is tested against a constant or pre-selected variable resistance

Question 15

An isokinetic dynamometer is used to

Accepted Answer

Isokinetic devices are a significant part of modern exercise testing and prescription and they are becoming essential for rehabilitation following injury

Question 16

Isometric or static testing is a situation when the muscle develops tension and the fibres shorten but no movement of the lever arm takes place

Accepted Answer

This is the definition of isometric testing

Question 17

Full extension of the leg is where the leg is bent to a 90° angle

Accepted Answer

Full extension is when the leg is straight and there is 180° position of the limb

Question 18

Isokinetic testing is when the limb is tested under a variable speed situation

Accepted Answer

Isokinetic is a term used to describe a situation where there is a muscle contraction during movement, but the rate of the movement is held at a constant pre-determined angular velocity

Question 19

An isokinetic dynamometer is a device that can test a limb in an isokinetic, isometric and isotonic mode

Accepted Answer

The modern devices are able to conduct a range of muscle testing

Question 20

It is usual to see true isokinetic dynamometers in the fitness centre or gymnasium

Accepted Answer

True isokinetic dynamometers are complex exercise and rehabilitation devices that generally are very expensive machines used only in hospitals or universities

Quiz 7: Measurement and Analysis Techniques