BSL PRO Lesson H17

Updated 01-07-11

BSL PRO Lesson H17: Biomechanics (Goniometry & EMG)

Overview

Goniometers are devices capable of transforming angular position into a proportional electrical signal. They

incorporate gauge elements that measure bending strain along or around a particular axis. The bending strain

is proportional to the sum total angular shift along the axis. Because the bending force is extremely small, the

output signal is uniquely a proportional function of the angular shift. The twin-axis goniometers used in this

study are dual output devices that can simultaneously measure angular rotation about two orthogonal planes.

A goniometer for humans is used to determine the position of a moveable joint and the available range and

quality of motion at the joint. Goniometry is useful in assessing abnormalities in joint movement associated with

disease, developing treatment strategies and goals, and evaluating progress toward those goals. The

combination of goniometry and electromyography (EMG) is prevalent in strength and conditioning studies.

Strength can be defined as the ability of a muscle to produce or resist a physical force. Force generated during

muscle contraction can be static (force producing no movement), as in isometric contraction, or dynamic (force

producing movement), as in isotonic contraction. Dynamic contractions occur when there is visible joint

movement and may be classified as either concentric or eccentric muscle contraction.

 Concentric contraction occurs if the resistance is less than the force produced by the muscle group.

This type of contraction allows the muscle to shorten as it exerts tension (e.g. slowly raising a

dumbbell).

 Eccentric contraction occurs when the muscle produces a braking force to decelerate rapidly moving

body segments or to resist gravity. The lowering of a dumbbell is an example of an eccentric

contraction.

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Objectives

1. To record muscle activity of both the triceps and the biceps muscles.

2. To observe limb angular movement of the elbow.

Equipment

 BIOPAC Electrode Lead Sets (2) (SS2L)

 BIOPAC Disposable Vinyl Electrodes (EL503), six per Subject

 BIOPAC Twin-axis Goniometer (180 mm) (SS21L)

 BIOPAC Adhesive Single-Sided Tape (TAPE1)

 BIOPAC Adhesive Double-Sided Tape (TAPE2)

 Dumbbell weights (two different weights)

 Computer running Windows XP or higher, or Mac OS X

 Biopac Student Lab PRO software

 BIOPAC Data Acquisition Unit (MP36/MP35/MP30)

Setup

Hardware

1. The SS21L connects to two channels:

Connect SS21L-X to CH 1 and

Connect SS21L-Y to CH 2.

2. Use two SS2L lead sets:

Connect one SS2L to CH 3 and

Connect the other SS2L to CH 4.

3. Turn on the MP unit.

Software

1. Launch the BSL PRO software on the host computer.

 The program should create a new "Untitled1" window.

2. Open the Biomechanics Template by choosing File > Open > choose Files of type: Graph Template

(*GTL) > File name: "H17 Biomechanics.gtl"

 The template will establish the required settings.

3. Save As the desired file name.

Calibration

1. Go to MP Menu>Setup Channels and click the wrench icon for CH 1 to change parameters.

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2. Click the Scaling... button to generate the Change Scaling Parameters dialog.

3. Click the Cal1 button.

 The Scale value should read “0.”

4. Click the Cal2 button.

 The Scale value should read “90.”

5. Make sure the twin-axis goniometer (SS21L) is lying flat and then position it straight at 180 and click

Cal1.

6. Rotate the top endblock to 90, keep it flat, and click Cal2.

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Subject

Triceps

Biceps

1. Attach six electrodes to the Subject, as shown below.

 Abrade each electrode site. It is a good idea to abrade the skin before electrode placement to

decrease the amount of impedance between the electrode and the skin's surface.

 Apply a small amount of electrode gel (GEL1) at each electrode site. A drop of electrode gel will

further improve electrode detection.

 Apply electrodes.

Position SS2L Lead Color

Triceps muscle (2) CH 3

red lead on top

white lead on bottom

Wrist—outside CH 3 black (ground)

Biceps muscle (2) CH 4

red lead on top

white lead on bottom

Wrist—inside CH4 black (ground)

2. Attach the electrode lead sets (SS2L) to the electrodes, paying close attention to the lead colors and

positions specified in the table above.

 Position the electrode cables so they do not pull on the electrodes.

 Clip the electrode cable clip (where the cable meets the three individual colored wires) to a

convenient location (such as Subject’s clothes) to relieve cable strain.

3. Attach the twin-axis goniometer (SS21L) to the Subject’s arm as shown below, to measure angular

rotation of the elbow.

 Attach pieces of double-sided tape to the underside of the goniometer endblocks.

 Stick the tape to the Subject and allow for the telescoping of the goniometer. The goniometer

should be fully extended when the joint is fully flexed.

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 Press the two endblocks firmly onto the Subject and ensure that the goniometer is lying over the

top of the joint.

 For additional security, pass a single wrap of single-sided medical tape around each endblock

and Subject's arm. Do not tape too tightly or you will restrict movement.

 Secure the cable and connector leaving the goniometer with tape to ensure that they do not pull

and detach the goniometer.

 See Application Note 140 for further information about using goniometers.

Hints for minimizing measurement error:

1. Apply the electrodes at least 5 minutes before recording. Sweating tends to affect electrode adhesion to

the skin.

2. Nothing should rub against the electrodes, and Subject’s clothing should not interfere with electrodes.

3. No pressure should be placed on the electrodes or the baseline will be distorted.

4. When using the goniometer:

 Take care to handle/manipulate the sensors as instructed.

 Observe the minimum value bend radius at all times, particularly when attaching and removing

the sensors from the Subject.

 Take care during mounting so that the measurement element always forms a simple bend

shape—an "oxbow" shape in the element will reduce accuracy.

 Remove the endblocks individually and carefully, making sure not to exceed the minimum

permissible bend radius, particularly where the measuring element enters the endblocks.

 Never pull on the measurement element and/or protective spring to remove the goniometer from

the Subject.

Note Mishandling may result in inaccurate data, reduced equipment life, or equipment failure.

Notes

This recording is set up for the Save Once mode, which tells the MP System to

automatically record data into a file and to store that data into computer

memory (RAM) during acquisition.

To save recorded data, choose File menu > Save As… > file type: BSL PRO

files (*.ACQ) File name: (Enter Name) > Save button

To erase all recorded data (make sure you have saved it first), and begin from

Time 0, choose: MP menu > Setup Acquisition > Click on "Reset"

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Running the Experiment

 Subject is referred to as "his" for brevity, but can be male or female.

Segment 1: no weight (control)

1. After all the equipment has been properly attached, have the Subject stand up.

2. Have the Subject slowly lift his arm toward his shoulder, simulating a curl.

3. Have the Subject slowly lower his arm toward his leg.

Segment 2: lighter dumbbell

1. The lab partner will hand the lighter dumbbell to the Subject.

2. Place a marker (click F9 on PC or Esc on Mac) and label it by weight and type.

 The marker text box is above the waveform.

3. Have the Subject slowly lift the dumbbell toward his chest.

4. Have the Subject slowly lower the dumbbell toward his leg.

Segment 3: heavier dumbbell

1. The lab partner will hand the heavier dumbbell to the Subject.

2. Place a marker (click F9 on PC or Esc on Mac) and label it by weight and type.

 The marker text box is above the waveform.

3. Have the Subject slowly lift the dumbbell toward his chest.

4. Have the Subject slowly lower the dumbbell toward his leg.

ANALYSIS

 The EMG & Goniometer study will be displayed as follows:

Channel Displays

CH 1 Goniometer

CH 2 not displayed

CH 3 Triceps (EMG)

CH 4 Biceps (EMG)

 Measurement boxes should be established as shown above—CH 1 and CH 4 as value.

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1. Use the I-beam tool to locate the angle where the maximum amount of muscle activity was done.

 Notice that this angle is approximately halfway between the ending and starting point of the

dumbbell curl.

Appendix

GRAPH TEMPLATE SETTINGS

Click here to open a PDF of the graph template file settings. The BSL PRO Graph Template file automatically

establishes the settings shown in the table.